Publications by authors named "Jean-Philippe Julien"

84 Publications

Molecular basis of human CD22 function and therapeutic targeting.

Nat Commun 2017 10 2;8(1):764. Epub 2017 Oct 2.

Program in Molecular Medicine, The Hospital for Sick Children Research Institute, Toronto, ON, Canada, M5G 0A4.

CD22 maintains a baseline level of B-cell inhibition to keep humoral immunity in check. As a B-cell-restricted antigen, CD22 is targeted in therapies against dysregulated B cells that cause autoimmune diseases and blood cancers. Here we report the crystal structure of human CD22 at 2.1 Å resolution, which reveals that specificity for α2-6 sialic acid ligands is dictated by a pre-formed β-hairpin as a unique mode of recognition across sialic acid-binding immunoglobulin-type lectins. The CD22 ectodomain adopts an extended conformation that facilitates concomitant CD22 nanocluster formation on B cells and binding to trans ligands to avert autoimmunity in mammals. We structurally delineate the CD22 site targeted by the therapeutic antibody epratuzumab at 3.1 Å resolution and determine a critical role for CD22 N-linked glycosylation in antibody engagement. Our studies provide molecular insights into mechanisms governing B-cell inhibition and valuable clues for the design of immune modulators in B-cell dysfunction.The B-cell-specific co-receptor CD22 is a therapeutic target for depleting dysregulated B cells. Here the authors structurally characterize the ectodomain of CD22 and present its crystal structure with the bound therapeutic antibody epratuzumab, which gives insights into the mechanism of inhibition of B-cell activation.
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http://dx.doi.org/10.1038/s41467-017-00836-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5624926PMC
October 2017

Improving the Immunogenicity of Native-like HIV-1 Envelope Trimers by Hyperstabilization.

Cell Rep 2017 Aug;20(8):1805-1817

Department of Medical Microbiology, Academic Medical Center, University of Amsterdam, Amsterdam 1105 AZ, the Netherlands; Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, NY 10021, USA. Electronic address:

The production of native-like recombinant versions of the HIV-1 envelope glycoprotein (Env) trimer requires overcoming the natural flexibility and instability of the complex. The engineered BG505 SOSIP.664 trimer mimics the structure and antigenicity of native Env. Here, we describe how the introduction of new disulfide bonds between the glycoprotein (gp)120 and gp41 subunits of SOSIP trimers of the BG505 and other genotypes improves their stability and antigenicity, reduces their conformational flexibility, and helps maintain them in the unliganded conformation. The resulting next-generation SOSIP.v5 trimers induce strong autologous tier-2 neutralizing antibody (NAb) responses in rabbits. In addition, the BG505 SOSIP.v6 trimers induced weak heterologous NAb responses against a subset of tier-2 viruses that were not elicited by the prototype BG505 SOSIP.664. These stabilization methods can be applied to trimers from multiple genotypes as components of multivalent vaccines aimed at inducing broadly NAbs (bNAbs).
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http://dx.doi.org/10.1016/j.celrep.2017.07.077DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5590011PMC
August 2017

A Broadly Neutralizing Antibody Targets the Dynamic HIV Envelope Trimer Apex via a Long, Rigidified, and Anionic β-Hairpin Structure.

Immunity 2017 04;46(4):690-702

Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92037, USA; Center for HIV/AIDS Vaccine Immunology and Immunogen Discovery, International AIDS Vaccine Initiative Neutralizing Antibody Center and Collaboration for AIDS Vaccine Discovery, The Scripps Research Institute, La Jolla, CA 92037, USA. Electronic address:

Broadly neutralizing antibodies (bnAbs) to HIV delineate vaccine targets and are prophylactic and therapeutic agents. Some of the most potent bnAbs target a quaternary epitope at the apex of the surface HIV envelope (Env) trimer. Using cryo-electron microscopy, we solved the atomic structure of an apex bnAb, PGT145, in complex with Env. We showed that the long anionic HCDR3 of PGT145 penetrated between glycans at the trimer 3-fold axis, to contact peptide residues from all three Env protomers, and thus explains its highly trimer-specific nature. Somatic hypermutation in the other CDRs of PGT145 were crucially involved in stabilizing the structure of the HCDR3, similar to bovine antibodies, to aid in recognition of a cluster of conserved basic residues hypothesized to facilitate trimer disassembly during viral entry. Overall, the findings exemplify the creative solutions that the human immune system can evolve to recognize a conserved motif buried under a canopy of glycans.
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http://dx.doi.org/10.1016/j.immuni.2017.03.017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5400778PMC
April 2017

Key Residues at Third CDR3β Position Impact Structure and Antigen Recognition of Human Invariant NK TCRs.

J Immunol 2017 02 21;198(3):1056-1065. Epub 2016 Dec 21.

Tumor Immunotherapy Program, Campbell Family Institute for Breast Cancer Research, Campbell Family Cancer Research Institute, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario M5G 2M9, Canada;

The human invariant NK (iNK) TCR is largely composed of the invariant TCR Vα24-Jα18 chain and semivariant TCR Vβ11 chains with variable CDR3β sequences. The direct role of CDR3β in Ag recognition has been studied extensively. Although it was noted that CDR3β can interact with CDR3α, how this interaction might indirectly influence Ag recognition is not fully elucidated. We observed that the third position of Vβ11 CDR3 can encode an Arg or Ser residue as a result of somatic rearrangement. Clonotypic analysis of the two iNK TCR types with a single amino acid substitution revealed that the staining intensity by anti-Vα24 Abs depends on whether Ser or Arg is encoded. When stained with an anti-Vα24-Jα18 Ab, human primary invariant NKT cells could be divided into Vα24 low- and high-intensity subsets, and Arg-encoding TCR Vβ11 chains were more frequently isolated from the Vα24 low-intensity subpopulation compared with the Vα24 high-intensity subpopulation. The Arg/Ser substitution also influenced Ag recognition as determined by CD1d multimer staining and CD1d-restricted functional responses. Importantly, in silico modeling validated that this Ser-to-Arg mutation could alter the structure of the CDR3β loop, as well as the CDR3α loop. Collectively, these results indicate that the Arg/Ser encoded at the third CDR3β residue can effectively modulate the overall structure of, and Ag recognition by, human iNK TCRs.
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http://dx.doi.org/10.4049/jimmunol.1601556DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5262525PMC
February 2017

Discrete TCR Binding Kinetics Control Invariant NKT Cell Selection and Central Priming.

J Immunol 2016 11 19;197(10):3959-3969. Epub 2016 Oct 19.

Department of Immunology, University of Toronto, Toronto, Ontario M5S 1A8, Canada;

Invariant NKT (iNKT) cells develop and differentiate in the thymus, segregating into iNKT1/2/17 subsets akin to Th1/2/17 classical CD4 T cells; however, iNKT TCRs recognize Ags in a fundamentally different way. How the biophysical parameters of iNKT TCRs influence signal strength in vivo and how such signals affect the development and differentiation of these cells are unknown. In this study, we manipulated TCRs in vivo to generate clonotypic iNKT cells using TCR retrogenic chimeras. We report that the biophysical properties of CD1d-lipid-TCR interactions differentially impacted the development and effector differentiation of iNKT cells. Whereas selection efficiency strongly correlated with TCR avidity, TCR signaling, cell-cell conjugate formation, and iNKT effector differentiation correlated with the half-life of CD1d-lipid-TCR interactions. TCR binding properties, however, did not modulate Ag-induced iNKT cytokine production. Our work establishes that discrete TCR interaction kinetics influence iNKT cell development and central priming.
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http://dx.doi.org/10.4049/jimmunol.1601382DOI Listing
November 2016

Minimally Mutated HIV-1 Broadly Neutralizing Antibodies to Guide Reductionist Vaccine Design.

PLoS Pathog 2016 08 25;12(8):e1005815. Epub 2016 Aug 25.

Department of Immunology and Microbial Science, The Scripps Research Institute, La Jolla, California, United States of America.

An optimal HIV vaccine should induce broadly neutralizing antibodies (bnAbs) that neutralize diverse viral strains and subtypes. However, potent bnAbs develop in only a small fraction of HIV-infected individuals, all contain rare features such as extensive mutation, insertions, deletions, and/or long complementarity-determining regions, and some are polyreactive, casting doubt on whether bnAbs to HIV can be reliably induced by vaccination. We engineered two potent VRC01-class bnAbs that minimized rare features. According to a quantitative features frequency analysis, the set of features for one of these minimally mutated bnAbs compared favorably with all 68 HIV bnAbs analyzed and was similar to antibodies elicited by common vaccines. This same minimally mutated bnAb lacked polyreactivity in four different assays. We then divided the minimal mutations into spatial clusters and dissected the epitope components interacting with those clusters, by mutational and crystallographic analyses coupled with neutralization assays. Finally, by synthesizing available data, we developed a working-concept boosting strategy to select the mutation clusters in a logical order following a germline-targeting prime. We have thus developed potent HIV bnAbs that may be more tractable vaccine goals compared to existing bnAbs, and we have proposed a strategy to elicit them. This reductionist approach to vaccine design, guided by antibody and antigen structure, could be applied to design candidate vaccines for other HIV bnAbs or protective Abs against other pathogens.
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http://dx.doi.org/10.1371/journal.ppat.1005815DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4999182PMC
August 2016

The structural basis of modified nucleosome recognition by 53BP1.

Nature 2016 08 27;536(7614):100-3. Epub 2016 Jul 27.

DNA double-strand breaks (DSBs) elicit a histone modification cascade that controls DNA repair. This pathway involves the sequential ubiquitination of histones H1 and H2A by the E3 ubiquitin ligases RNF8 and RNF168, respectively. RNF168 ubiquitinates H2A on lysine 13 and lysine 15 (refs 7, 8) (yielding H2AK13ub and H2AK15ub, respectively), an event that triggers the recruitment of 53BP1 (also known as TP53BP1) to chromatin flanking DSBs. 53BP1 binds specifically to H2AK15ub-containing nucleosomes through a peptide segment termed the ubiquitination-dependent recruitment motif (UDR), which requires the simultaneous engagement of histone H4 lysine 20 dimethylation (H4K20me2) by its tandem Tudor domain. How 53BP1 interacts with these two histone marks in the nucleosomal context, how it recognizes ubiquitin, and how it discriminates between H2AK13ub and H2AK15ub is unknown. Here we present the electron cryomicroscopy (cryo-EM) structure of a dimerized human 53BP1 fragment bound to a H4K20me2-containing and H2AK15ub-containing nucleosome core particle (NCP-ubme) at 4.5 Å resolution. The structure reveals that H4K20me2 and H2AK15ub recognition involves intimate contacts with multiple nucleosomal elements including the acidic patch. Ubiquitin recognition by 53BP1 is unusual and involves the sandwiching of the UDR segment between ubiquitin and the NCP surface. The selectivity for H2AK15ub is imparted by two arginine fingers in the H2A amino-terminal tail, which straddle the nucleosomal DNA and serve to position ubiquitin over the NCP-bound UDR segment. The structure of the complex between NCP-ubme and 53BP1 reveals the basis of 53BP1 recruitment to DSB sites and illuminates how combinations of histone marks and nucleosomal elements cooperate to produce highly specific chromatin responses, such as those elicited following chromosome breaks.
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http://dx.doi.org/10.1038/nature18951DOI Listing
August 2016

HIV-1 broadly neutralizing antibody precursor B cells revealed by germline-targeting immunogen.

Science 2016 Mar;351(6280):1458-63

Department of Immunology and Microbial Science, The Scripps Research Institute, La Jolla, CA 92037, USA. IAVI Neutralizing Antibody Center, The Scripps Research Institute, La Jolla, CA 92037, USA. Center for HIV/AIDS Vaccine Immunology and Immunogen Discovery, The Scripps Research Institute, La Jolla, CA 92037, USA. Ragon Institute of MGH, MIT, and Harvard, Cambridge, MA 02129, USA.

Induction of broadly neutralizing antibodies (bnAbs) is a major HIV vaccine goal. Germline-targeting immunogens aim to initiate bnAb induction by activating bnAb germline precursor B cells. Critical unmet challenges are to determine whether bnAb precursor naïve B cells bind germline-targeting immunogens and occur at sufficient frequency in humans for reliable vaccine responses. Using deep mutational scanning and multitarget optimization, we developed a germline-targeting immunogen (eOD-GT8) for diverse VRC01-class bnAbs. We then used the immunogen to isolate VRC01-class precursor naïve B cells from HIV-uninfected donors. Frequencies of true VRC01-class precursors, their structures, and their eOD-GT8 affinities support this immunogen as a candidate human vaccine prime. These methods could be applied to germline targeting for other classes of HIV bnAbs and for Abs to other pathogens.
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http://dx.doi.org/10.1126/science.aad9195DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4872700PMC
March 2016

EspP, an Extracellular Serine Protease from Enterohemorrhagic E. coli, Reduces Coagulation Factor Activities, Reduces Clot Strength, and Promotes Clot Lysis.

PLoS One 2016 2;11(3):e0149830. Epub 2016 Mar 2.

Department of Clinical Pathology, Sunnybrook Health Sciences Centre, Toronto, ON, Canada.

Background: EspP (E. coli secreted serine protease, large plasmid encoded) is an extracellular serine protease produced by enterohemorrhagic E. coli (EHEC) O157:H7, a causative agent of diarrhea-associated Hemolytic Uremic Syndrome (D+HUS). The mechanism by which EHEC induces D+HUS has not been fully elucidated.

Objectives: We investigated the effects of EspP on clot formation and lysis in human blood.

Methods: Human whole blood and plasma were incubated with EspP(WT )at various concentrations and sampled at various time points. Thrombin time (TT), prothrombin time (PT), and activated partial thromboplastin time (aPTT), coagulation factor activities, and thrombelastgraphy (TEG) were measured.

Results And Conclusions: Human whole blood or plasma incubated with EspP(WT) was found to have prolonged PT, aPTT, and TT. Furthermore, human whole blood or plasma incubated with EspP(WT) had reduced activities of coagulation factors V, VII, VIII, and XII, as well as prothrombin. EspP did not alter the activities of coagulation factors IX, X, or XI. When analyzed by whole blood TEG, EspP decreased the maximum amplitude of the clot, and increased the clot lysis. Our results indicate that EspP alters hemostasis in vitro by decreasing the activities of coagulation factors V, VII, VIII, and XII, and of prothrombin, by reducing the clot strength and accelerating fibrinolysis, and provide further evidence of a functional role for this protease in the virulence of EHEC and the development of D+HUS.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0149830PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4775034PMC
July 2016

Immunogenicity of Stabilized HIV-1 Envelope Trimers with Reduced Exposure of Non-neutralizing Epitopes.

Cell 2015 Dec;163(7):1702-15

Department of Integrative Structural and Computational Biology, Scripps CHAVI-ID, IAVI Neutralizing Antibody Center and Collaboration for AIDS Vaccine Discovery (CAVD), The Scripps Research Institute, La Jolla, CA 92037, USA.

The envelope glycoprotein trimer mediates HIV-1 entry into cells. The trimer is flexible, fluctuating between closed and more open conformations and sometimes sampling the fully open, CD4-bound form. We hypothesized that conformational flexibility and transient exposure of non-neutralizing, immunodominant epitopes could hinder the induction of broadly neutralizing antibodies (bNAbs). We therefore modified soluble Env trimers to stabilize their closed, ground states. The trimer variants were indeed stabilized in the closed conformation, with a reduced ability to undergo receptor-induced conformational changes and a decreased exposure of non-neutralizing V3-directed antibody epitopes. In rabbits, the stabilized trimers induced similar autologous Tier-1B or Tier-2 NAb titers to those elicited by the corresponding wild-type trimers but lower levels of V3-directed Tier-1A NAbs. Stabilized, closed trimers might therefore be useful components of vaccines aimed at inducing bNAbs.
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http://dx.doi.org/10.1016/j.cell.2015.11.056DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4732737PMC
December 2015

Design and structure of two HIV-1 clade C SOSIP.664 trimers that increase the arsenal of native-like Env immunogens.

Proc Natl Acad Sci U S A 2015 Sep 8;112(38):11947-52. Epub 2015 Sep 8.

Department of Integrative Structural and Computational Biology, International AIDS Vaccine Initiative ( IAVI) Neutralizing Antibody Center, Collaboration for AIDS Vaccine Discovery, Center for HIV/AIDS Vaccine Immunology and Immunogen Discovery, The Scripps Research Institute, La Jolla, CA 92037; The Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, CA 92037

A key challenge in the quest toward an HIV-1 vaccine is design of immunogens that can generate a broadly neutralizing antibody (bnAb) response against the enormous sequence diversity of the HIV-1 envelope glycoprotein (Env). We previously demonstrated that a recombinant, soluble, fully cleaved SOSIP.664 trimer based on the clade A BG505 sequence is a faithful antigenic and structural mimic of the native trimer in its prefusion conformation. Here, we sought clade C native-like trimers with comparable properties. We identified DU422 and ZM197M SOSIP.664 trimers as being appropriately thermostable (Tm of 63.4 °C and 62.7 °C, respectively) and predominantly native-like, as determined by negative-stain electron microscopy (EM). Size exclusion chromatography, ELISA, and surface plasmon resonance further showed that these trimers properly display epitopes for all of the major bnAb classes, including quaternary-dependent, trimer-apex (e.g., PGT145) and gp120/gp41 interface (e.g., PGT151) epitopes. A cryo-EM reconstruction of the ZM197M SOSIP.664 trimer complexed with VRC01 Fab against the CD4 binding site at subnanometer resolution revealed a striking overall similarity to its BG505 counterpart with expected local conformational differences in the gp120 V1, V2, and V4 loops. These stable clade C trimers contribute additional diversity to the pool of native-like Env immunogens as key components of strategies to induce bnAbs to HIV-1.
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http://dx.doi.org/10.1073/pnas.1507793112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4586835PMC
September 2015

Origins of a Vaccine-Induced, Human Anti-HIV-1 Antibody.

EBioMedicine 2015 Jul 16;2(7):632-3. Epub 2015 Jul 16.

Program in Molecular Structure and Function, The Hospital for Sick Children Research Institute, Toronto, Ontario M5G 0A4, Canada.

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http://dx.doi.org/10.1016/j.ebiom.2015.07.019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4534699PMC
July 2015

HIV-1 VACCINES. HIV-1 neutralizing antibodies induced by native-like envelope trimers.

Science 2015 Jul 18;349(6244):aac4223. Epub 2015 Jun 18.

Department of Immunology and Microbial Science, Scripps Research Institute, La Jolla, CA 92037, USA. International AIDS Vaccine Initiative, Neutralizing Antibody Center, and Collaboration for AIDS Vaccine Discovery, Scripps Research Institute, La Jolla, CA 92037, USA. Center for HIV/AIDS Vaccine Immunology and Immunogen Discovery, Scripps Research Institute, La Jolla, CA 92037, USA. International AIDS Vaccine Initiative, New York, NY 10004, USA. Ragon Institute of Massachusetts General Hospital, MIT, and Harvard, Boston, MA 02114, USA.

A challenge for HIV-1 immunogen design is the difficulty of inducing neutralizing antibodies (NAbs) against neutralization-resistant (tier 2) viruses that dominate human transmissions. We show that a soluble recombinant HIV-1 envelope glycoprotein trimer that adopts a native conformation, BG505 SOSIP.664, induced NAbs potently against the sequence-matched tier 2 virus in rabbits and similar but weaker responses in macaques. The trimer also consistently induced cross-reactive NAbs against more sensitive (tier 1) viruses. Tier 2 NAbs recognized conformational epitopes that differed between animals and in some cases overlapped with those recognized by broadly neutralizing antibodies (bNAbs), whereas tier 1 responses targeted linear V3 epitopes. A second trimer, B41 SOSIP.664, also induced a strong autologous tier 2 NAb response in rabbits. Thus, native-like trimers represent a promising starting point for the development of HIV-1 vaccines aimed at inducing bNAbs.
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http://dx.doi.org/10.1126/science.aac4223DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4498988PMC
July 2015

Redesigned HIV antibodies exhibit enhanced neutralizing potency and breadth.

J Clin Invest 2015 Jun 18;125(6):2523-31. Epub 2015 May 18.

Several HIV envelope-targeting (Env-targeting) antibodies with broad and potent neutralizing activity have been identified and shown to have unusual features. Of these, the PG9 antibody has a long heavy chain complementarity determining region 3 (HCDR3) and possesses unique structural elements that interact with protein and glycan features of the HIV Env glycoprotein. Here, we used the Rosetta software suite to design variants of the PG9 antibody HCDR3 loop with the goal of identifying variants with increased potency and breadth of neutralization for diverse HIV strains. One variant, designated PG9_N100(F)Y, possessed increased potency and was able to neutralize a diverse set of PG9-resistant HIV strains, including those lacking the Env N160 glycan, which is critical for PG9 binding. An atomic resolution structure of the PG9_N100(F)Y fragment antigen binding (Fab) confirmed that the mutated residue retains the paratope surface when compared with WT PG9. Differential scanning calorimetry experiments revealed that the mutation caused a modest increase in thermodynamic stability of the Fab, a feature predicted by the computational model. Our findings suggest that thermodynamic stabilization of the long HCDR3 in its active conformation is responsible for the increased potency of PG9_N100(F)Y, and strategies aimed at stabilizing this region in other HIV antibodies could become an important approach to in silico optimization of antibodies.
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http://dx.doi.org/10.1172/JCI80693DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4497764PMC
June 2015

Comprehensive antigenic map of a cleaved soluble HIV-1 envelope trimer.

PLoS Pathog 2015 Mar 25;11(3):e1004767. Epub 2015 Mar 25.

Department of Medical Microbiology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands; Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York, United States of America.

The trimeric envelope (Env) spike is the focus of vaccine design efforts aimed at generating broadly neutralizing antibodies (bNAbs) to protect against HIV-1 infection. Three recent developments have facilitated a thorough investigation of the antigenic structure of the Env trimer: 1) the isolation of many bNAbs against multiple different epitopes; 2) the generation of a soluble trimer mimic, BG505 SOSIP.664 gp140, that expresses most bNAb epitopes; 3) facile binding assays involving the oriented immobilization of tagged trimers. Using these tools, we generated an antigenic map of the trimer by antibody cross-competition. Our analysis delineates three well-defined epitope clusters (CD4 binding site, quaternary V1V2 and Asn332-centered oligomannose patch) and new epitopes at the gp120-gp41 interface. It also identifies the relationships among these clusters. In addition to epitope overlap, we defined three more ways in which antibodies can cross-compete: steric competition from binding to proximal but non-overlapping epitopes (e.g., PGT151 inhibition of 8ANC195 binding); allosteric inhibition (e.g., PGT145 inhibition of 1NC9, 8ANC195, PGT151 and CD4 binding); and competition by reorientation of glycans (e.g., PGT135 inhibition of CD4bs bNAbs, and CD4bs bNAb inhibition of 8ANC195). We further demonstrate that bNAb binding can be complex, often affecting several other areas of the trimer surface beyond the epitope. This extensive analysis of the antigenic structure and the epitope interrelationships of the Env trimer should aid in design of both bNAb-based therapies and vaccines intended to induce bNAbs.
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http://dx.doi.org/10.1371/journal.ppat.1004767DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4373910PMC
March 2015

Antibody potency relates to the ability to recognize the closed, pre-fusion form of HIV Env.

Nat Commun 2015 Feb 5;6:6144. Epub 2015 Feb 5.

Department of Medicinal Chemistry, University of Washington, Box 357610, Seattle, Washington 98195, USA.

HIV's envelope glycoprotein (Env) is the sole target for neutralizing antibodies. The structures of many broadly neutralizing antibodies (bNAbs) in complex with truncated Env subunits or components have been reported. However, their interaction with the intact Env trimer, and the structural determinants that underlie neutralization resistance in this more native context are less well understood. Here we use hydrogen/deuterium exchange to examine the interactions between a panel of bNAbs and native-like Env trimers (SOSIP.664 trimers). Highly potent bNAbs cause only localized effects at their binding interface, while the binding of less potent antibodies is associated with elaborate changes throughout the trimer. In conjunction with binding kinetics, our results suggest that poorly neutralizing antibodies can only bind when the trimer transiently samples an open state. We propose that the kinetics of such opening motions varies among isolates, with Env from neutralization-sensitive viruses opening more frequently than Env from resistant viruses.
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http://dx.doi.org/10.1038/ncomms7144DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4338595PMC
February 2015

A native-like SOSIP.664 trimer based on an HIV-1 subtype B env gene.

J Virol 2015 Mar 14;89(6):3380-95. Epub 2015 Jan 14.

Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York, USA

Unlabelled: Recombinant trimeric mimics of the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (Env) spike should expose as many epitopes as possible for broadly neutralizing antibodies (bNAbs) but few, if any, for nonneutralizing antibodies (non-NAbs). Soluble, cleaved SOSIP.664 gp140 trimers based on the subtype A strain BG505 approach this ideal and are therefore plausible vaccine candidates. Here, we report on the production and in vitro properties of a new SOSIP.664 trimer derived from a subtype B env gene, B41, including how to make this protein in low-serum media without proteolytic damage (clipping) to the V3 region. We also show that nonclipped trimers can be purified successfully via a positive-selection affinity column using the bNAb PGT145, which recognizes a quaternary structure-dependent epitope at the trimer apex. Negative-stain electron microscopy imaging shows that the purified, nonclipped, native-like B41 SOSIP.664 trimers contain two subpopulations, which we propose represent an equilibrium between the fully closed and a more open conformation. The latter is different from the fully open, CD4 receptor-bound conformation and may represent an intermediate state of the trimer. This new subtype B trimer adds to the repertoire of native-like Env proteins that are suitable for immunogenicity and structural studies.

Importance: The cleaved, trimeric envelope protein complex is the only neutralizing antibody target on the HIV-1 surface. Many vaccine strategies are based on inducing neutralizing antibodies. For HIV-1, one approach involves using recombinant, soluble protein mimics of the native trimer. At present, the only reliable way to make native-like, soluble trimers in practical amounts is via the introduction of specific sequence changes that confer stability on the cleaved form of Env. The resulting proteins are known as SOSIP.664 gp140 trimers, and the current paradigm is based on the BG505 subtype A env gene. Here, we describe the production and characterization of a SOSIP.664 protein derived from a subtype B gene (B41), together with a simple, one-step method to purify native-like trimers by affinity chromatography with a trimer-specific bNAb, PGT145. The resulting trimers will be useful for structural and immunogenicity experiments aimed at devising ways to make an effective HIV-1 vaccine.
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http://dx.doi.org/10.1128/JVI.03473-14DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4337520PMC
March 2015

Recombinant HIV envelope trimer selects for quaternary-dependent antibodies targeting the trimer apex.

Proc Natl Acad Sci U S A 2014 Dec 24;111(49):17624-9. Epub 2014 Nov 24.

Department of Immunology and Microbial Science, International AIDS Vaccine Initiative Neutralizing Antibody Center, Center for HIV/AIDS Vaccine Immunology and Immunogen Discovery, Ragon Institute of Massachusetts General Hospital, Massachusetts Institute of Technology and Harvard University, Boston, MA 02142

Broadly neutralizing antibodies (bnAbs) targeting the trimer apex of HIV envelope are favored candidates for vaccine design and immunotherapy because of their great neutralization breadth and potency. However, methods of isolating bnAbs against this site have been limited by the quaternary nature of the epitope region. Here we report the use of a recombinant HIV envelope trimer, BG505 SOSIP.664 gp140, as an affinity reagent to isolate quaternary-dependent bnAbs from the peripheral blood mononuclear cells of a chronically infected donor. The newly isolated bnAbs, named "PGDM1400-1412," show a wide range of neutralization breadth and potency. One of these variants, PGDM1400, is exceptionally broad and potent with cross-clade neutralization coverage of 83% at a median IC50 of 0.003 µg/mL. Overall, our results highlight the utility of BG505 SOSIP.664 gp140 as a tool for the isolation of quaternary-dependent antibodies and reveal a mosaic of antibody responses against the trimer apex within a clonal family.
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http://dx.doi.org/10.1073/pnas.1415789111DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4267403PMC
December 2014

Structural evolution of glycan recognition by a family of potent HIV antibodies.

Cell 2014 Sep;159(1):69-79

Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92037, USA; International AIDS Vaccine Initiative Neutralizing Antibody Center, The Scripps Research Institute, La Jolla, CA 92037, USA; Scripps Center for HIV/AIDS Vaccine Immunology & Immunogen Discovery, The Scripps Research Institute, La Jolla, CA 92037, USA; Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, CA 92037, USA. Electronic address:

The HIV envelope glycoprotein (Env) is densely covered with self-glycans that should help shield it from recognition by the human immune system. Here, we examine how a particularly potent family of broadly neutralizing antibodies (Abs) has evolved common and distinct structural features to counter the glycan shield and interact with both glycan and protein components of HIV Env. The inferred germline antibody already harbors potential binding pockets for a glycan and a short protein segment. Affinity maturation then leads to divergent evolutionary branches that either focus on a single glycan and protein segment (e.g., Ab PGT124) or engage multiple glycans (e.g., Abs PGT121-123). Furthermore, other surrounding glycans are avoided by selecting an appropriate initial antibody shape that prevents steric hindrance. Such molecular recognition lessons are important for engineering proteins that can recognize or accommodate glycans.
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http://dx.doi.org/10.1016/j.cell.2014.09.009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4278586PMC
September 2014

Structure of 2G12 Fab2 in complex with soluble and fully glycosylated HIV-1 Env by negative-stain single-particle electron microscopy.

J Virol 2014 Sep 25;88(17):10177-88. Epub 2014 Jun 25.

Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, California, USA International AIDS Vaccine Initiative Neutralizing Antibody Center and Center for HIV/AIDS Vaccine Immunology and Immunogen Discovery, The Scripps Research Institute, La Jolla, California, USA

Unlabelled: The neutralizing anti-HIV-1 antibody 2G12 is of particular interest due to the sterilizing protection it provides from viral challenge in animal models. 2G12 is a unique, domain-exchanged antibody that binds exclusively to conserved N-linked glycans that form the high-mannose patch on the gp120 outer domain centered on a glycan at position N332. Several glycans in and around the 2G12 epitope have been shown to interact with other potent, broadly neutralizing antibodies; therefore, this region constitutes a supersite of vulnerability on gp120. While crystal structures of 2G12 and 2G12 bound to high-mannose glycans have been solved, no structural information that describes the interaction of 2G12 with gp120 or the Env trimer is available. Here, we present a negative-stain single-particle electron microscopy reconstruction of 2G12 Fab2 in complex with a soluble, trimeric Env at ∼17-Å resolution that reveals the antibody's interaction with its native and fully glycosylated epitope. We also mapped relevant glycans in this epitope by fitting high-resolution crystal structures and by performing neutralization assays of glycan knockouts. In addition, a reconstruction at ∼26 Å of the ternary complex formed by 2G12 Fab2, soluble CD4, and Env indicates that 2G12 may block membrane fusion by induced steric hindrance upon primary receptor binding, thereby abrogating Env's interaction with coreceptor(s). These structures provide a basis for understanding 2G12 binding and neutralization, and our low-resolution model and glycan assignments provide a basis for higher-resolution studies to determine the molecular nature of the 2G12 epitope.

Importance: HIV-1 is a human virus that results in the deaths of millions of people around the world each year. While there are several effective therapeutics available to prolong life, a vaccine is the best long-term solution for curbing this global epidemic. Here, we present structural data that reveal the viral binding site of one of the first HIV-1-neutralizing antibodies isolated, 2G12, and provide a rationale for its effectiveness. These structures provide a basis for higher-resolution studies to determine the molecular nature of the 2G12 epitope, which will aid in vaccine design and antibody-based therapies.
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http://dx.doi.org/10.1128/JVI.01229-14DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4136306PMC
September 2014

CD4-induced activation in a soluble HIV-1 Env trimer.

Structure 2014 Jul 12;22(7):974-84. Epub 2014 Jun 12.

Department of Medicinal Chemistry, University of Washington, Seattle, WA 98195, USA. Electronic address:

The HIV envelope glycoprotein (Env) trimer undergoes receptor-induced conformational changes that drive fusion of the viral and cellular membranes. Env conformational changes have been observed using low-resolution electron microscopy, but only large-scale rearrangements have been visible. Here, we use hydrogen-deuterium exchange and oxidative labeling to gain a more precise understanding of the unliganded and CD4-bound forms of soluble Env trimers (SOSIP.664), including their glycan composition. CD4 activation induces the reorganization of bridging sheet elements, V1/V2 and V3, much of the gp120 inner domain, and the gp41 fusion subunit. Two CD4 binding site-targeted inhibitors have substantially different effects: NBD-556 partially mimics CD4-induced destabilization of the V1/V2 and V3 crown, whereas BMS-806 only affects regions around the gp120/gp41 interface. The structural information presented here increases our knowledge of CD4- and small molecule-induced conformational changes in Env and the allosteric pathways that lead to membrane fusion.
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http://dx.doi.org/10.1016/j.str.2014.05.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4231881PMC
July 2014

Differential binding of neutralizing and non-neutralizing antibodies to native-like soluble HIV-1 Env trimers, uncleaved Env proteins, and monomeric subunits.

Retrovirology 2014 May 29;11:41. Epub 2014 May 29.

Department of Microbiology and Immunology, Weill Cornell Medical College, Cornell University, New York, USA.

Background: The trimeric envelope glycoproteins (Env) on the surface of HIV-1 virions are the targets for neutralizing antibodies (NAbs). No candidate HIV-1 immunogen has yet induced potent, broadly active NAbs (bNAbs). Part of the explanation may be that previously tested Env proteins inadequately mimic the functional, native Env complex. Trimerization and the proteolytic processing of Env precursors into gp120 and gp41 profoundly alter antigenicity, but soluble cleaved trimers are too unstable to serve as immunogens. By introducing stabilizing mutations (SOSIP), we constructed soluble, cleaved Env trimers derived from the HIV-1 subtype A isolate BG505 that resemble native Env spikes on virions both structurally and antigenically.

Results: We used surface plasmon resonance (SPR) to quantify antibody binding to different forms of BG505 Env: the proteolytically cleaved SOSIP.664 trimers, cleaved gp120-gp41ECTO protomers, and gp120 monomers. Non-NAbs to the CD4-binding site bound only marginally to the trimers but equally well to gp120-gp41ECTO protomers and gp120 monomers, whereas the bNAb VRC01, directed to the CD4bs, bound to all three forms. In contrast, bNAbs to V1V2 glycan-dependent epitopes bound preferentially (PG9 and PG16) or exclusively (PGT145) to trimers. We also explored the antigenic consequences of three different features of SOSIP.664 gp140 trimers: the engineered inter-subunit disulfide bond, the trimer-stabilizing I559P change in gp41ECTO, and proteolytic cleavage at the gp120-gp41ECTO junction. Each of these three features incrementally promoted native-like trimer antigenicity. We compared Fab and IgG versions of bNAbs and validated a bivalent model of IgG binding. The NAbs showed widely divergent binding kinetics and degrees of binding to native-like BG505 SOSIP.664. High off-rate constants and low stoichiometric estimates of NAb binding were associated with large amounts of residual infectivity after NAb neutralization of the corresponding BG505.T332N pseudovirus.

Conclusions: The antigenicity and structural integrity of cleaved BG505 SOSIP.664 trimers render these proteins good mimics of functional Env spikes on virions. In contrast, uncleaved gp140s antigenically resemble individual gp120-gp41ECTO protomers and gp120 monomers, but not native trimers. Although NAb binding to functional trimers may thus be both necessary and sufficient for neutralization, the kinetics and stoichiometry of the interaction influence the neutralizing efficacy of individual NAbs.
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http://dx.doi.org/10.1186/1742-4690-11-41DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4067080PMC
May 2014

Promiscuous glycan site recognition by antibodies to the high-mannose patch of gp120 broadens neutralization of HIV.

Sci Transl Med 2014 May;6(236):236ra63

Department of Immunology and Microbial Science, The Scripps Research Institute, La Jolla, CA 92037, USA. International AIDS Vaccine Initiative Neutralizing Antibody Center, The Scripps Research Institute, La Jolla, CA 92037, USA. Center for HIV/AIDS Vaccine Immunology and Immunogen Discovery, The Scripps Research Institute, La Jolla, CA 92037, USA. Ragon Institute of Massachusetts General Hospital, Massachusetts Institute of Technology, and Harvard University, Boston, MA 02142, USA.

Broadly neutralizing monoclonal antibodies (bnmAbs) that target the high-mannose patch centered around the glycan at position 332 on HIV Env are promising vaccine leads and therapeutic candidates because they effectively protect against mucosal SHIV challenge and strongly suppress SHIV viremia in established infection in macaque models. However, these antibodies demonstrate varying degrees of dependency on the N332 glycan site, and the origins of their neutralization breadth are not always obvious. By measuring neutralization on an extended range of glycan site viral variants, we found that some bnmAbs can use alternate N-linked glycans in the absence of the N332 glycan site and therefore neutralize a substantial number of viruses lacking the site. Furthermore, many of the antibodies can neutralize viruses in which the N332 glycan site is shifted to the 334 position. Finally, we found that a combination of three antibody families that target the high-mannose patch can lead to 99% neutralization coverage of a large panel of viruses containing the N332/N334 glycan site and up to 66% coverage for viruses that lack the N332/N334 glycan site. The results indicate that a diverse response against the high-mannose patch may provide near-equivalent coverage as a combination of bnmAbs targeting multiple epitopes. Additionally, the ability of some bnmAbs to use other N-linked glycan sites can help counter neutralization escape mediated by shifting of glycosylation sites. Overall, this work highlights the importance of promiscuous glycan binding properties in bnmAbs to the high-mannose patch for optimal antiviral activity in either protective or therapeutic modalities.
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http://dx.doi.org/10.1126/scitranslmed.3008104DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4095976PMC
May 2014

Structural delineation of a quaternary, cleavage-dependent epitope at the gp41-gp120 interface on intact HIV-1 Env trimers.

Immunity 2014 May 24;40(5):669-80. Epub 2014 Apr 24.

Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92037, USA; IAVI Neutralizing Antibody Center, The Scripps Research Institute, La Jolla, CA 92037, USA; Center for HIV/AIDS Vaccine Immunology and Immunogen Discovery, The Scripps Research Institute, La Jolla, CA 92037, USA. Electronic address:

All previously characterized broadly neutralizing antibodies to the HIV-1 envelope glycoprotein (Env) target one of four major sites of vulnerability. Here, we define and structurally characterize a unique epitope on Env that is recognized by a recently discovered family of human monoclonal antibodies (PGT151-PGT158). The PGT151 epitope is comprised of residues and glycans at the interface of gp41 and gp120 within a single protomer and glycans from both subunits of a second protomer and represents a neutralizing epitope that is dependent on both gp120 and gp41. Because PGT151 binds only to properly formed, cleaved trimers, this distinctive property, and its ability to stabilize Env trimers, has enabled the successful purification of mature, cleaved Env trimers from the cell surface as a complex with PGT151. Here we compare the structural and functional properties of membrane-extracted Env trimers from several clades with those of the soluble, cleaved SOSIP gp140 trimer.
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http://dx.doi.org/10.1016/j.immuni.2014.04.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4057017PMC
May 2014

The effects of somatic hypermutation on neutralization and binding in the PGT121 family of broadly neutralizing HIV antibodies.

PLoS Pathog 2013 21;9(11):e1003754. Epub 2013 Nov 21.

Department of Immunology and Microbial Science, The Scripps Research Institute, La Jolla, California, United States of America ; IAVI Neutralizing Antibody Center, The Scripps Research Institute, La Jolla, California, United States of America ; Scripps Center for HIV/AIDS Vaccine Immunology and Immunogen Discovery, The Scripps Research Institute, La Jolla, California, United States of America.

Broadly neutralizing HIV antibodies (bnAbs) are typically highly somatically mutated, raising doubts as to whether they can be elicited by vaccination. We used 454 sequencing and designed a novel phylogenetic method to model lineage evolution of the bnAbs PGT121-134 and found a positive correlation between the level of somatic hypermutation (SHM) and the development of neutralization breadth and potency. Strikingly, putative intermediates were characterized that show approximately half the mutation level of PGT121-134 but were still capable of neutralizing roughly 40-80% of PGT121-134 sensitive viruses in a 74-virus panel at median titers between 15- and 3-fold higher than PGT121-134. Such antibodies with lower levels of SHM may be more amenable to elicitation through vaccination while still providing noteworthy coverage. Binding characterization indicated a preference of inferred intermediates for native Env binding over monomeric gp120, suggesting that the PGT121-134 lineage may have been selected for binding to native Env at some point during maturation. Analysis of glycan-dependent neutralization for inferred intermediates identified additional adjacent glycans that comprise the epitope and suggests changes in glycan dependency or recognition over the course of affinity maturation for this lineage. Finally, patterns of neutralization of inferred bnAb intermediates suggest hypotheses as to how SHM may lead to potent and broad HIV neutralization and provide important clues for immunogen design.
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http://dx.doi.org/10.1371/journal.ppat.1003754DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3836729PMC
June 2014

Cryo-EM structure of a fully glycosylated soluble cleaved HIV-1 envelope trimer.

Science 2013 Dec 31;342(6165):1484-90. Epub 2013 Oct 31.

National Resource for Automated Molecular Microscopy, The Scripps Research Institute, La Jolla, CA 92037, USA.

The HIV-1 envelope glycoprotein (Env) trimer contains the receptor binding sites and membrane fusion machinery that introduce the viral genome into the host cell. As the only target for broadly neutralizing antibodies (bnAbs), Env is a focus for rational vaccine design. We present a cryo-electron microscopy reconstruction and structural model of a cleaved, soluble Env trimer (termed BG505 SOSIP.664 gp140) in complex with a CD4 binding site (CD4bs) bnAb, PGV04, at 5.8 angstrom resolution. The structure reveals the spatial arrangement of Env components, including the V1/V2, V3, HR1, and HR2 domains, as well as shielding glycans. The structure also provides insights into trimer assembly, gp120-gp41 interactions, and the CD4bs epitope cluster for bnAbs, which covers a more extensive area and defines a more complex site of vulnerability than previously described.
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http://dx.doi.org/10.1126/science.1245627DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3954647PMC
December 2013

Crystal structure of a soluble cleaved HIV-1 envelope trimer.

Science 2013 Dec 31;342(6165):1477-83. Epub 2013 Oct 31.

Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.

HIV-1 entry into CD4(+) target cells is mediated by cleaved envelope glycoprotein (Env) trimers that have been challenging to characterize structurally. Here, we describe the crystal structure at 4.7 angstroms of a soluble, cleaved Env trimer that is stabilized and antigenically near-native (termed the BG505 SOSIP.664 gp140 trimer) in complex with a potent broadly neutralizing antibody, PGT122. The structure shows a prefusion state of gp41, the interaction between the component gp120 and gp41 subunits, and how a close association between the gp120 V1/V2/V3 loops stabilizes the trimer apex around the threefold axis. The complete epitope of PGT122 on the trimer involves gp120 V1, V3, and several surrounding glycans. This trimer structure advances our understanding of how Env functions and is presented to the immune system, and provides a blueprint for structure-based vaccine design.
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http://dx.doi.org/10.1126/science.1245625DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3886632PMC
December 2013

Cleavage strongly influences whether soluble HIV-1 envelope glycoprotein trimers adopt a native-like conformation.

Proc Natl Acad Sci U S A 2013 Nov 21;110(45):18256-61. Epub 2013 Oct 21.

Department of Microbiology and Immunology, Weill Cornell Medical College, New York, NY 10065.

We compare the antigenicity and conformation of soluble, cleaved vs. uncleaved envelope glycoprotein (Env gp)140 trimers from the subtype A HIV type 1 (HIV-1) strain BG505. The impact of gp120-gp41 cleavage on trimer structure, in the presence or absence of trimer-stabilizing modifications (i.e., a gp120-gp41 disulfide bond and an I559P gp41 change, together designated SOSIP), was assessed. Without SOSIP changes, cleaved trimers disintegrate into their gp120 and gp41-ectodomain (gp41ECTO) components; when only the disulfide bond is present, they dissociate into gp140 monomers. Uncleaved gp140s remain trimeric whether SOSIP substitutions are present or not. However, negative-stain electron microscopy reveals that only cleaved trimers form homogeneous structures resembling native Env spikes on virus particles. In contrast, uncleaved trimers are highly heterogeneous, adopting a variety of irregular shapes, many of which appear to be gp120 subunits dangling from a central core that is presumably a trimeric form of gp41ECTO. Antigenicity studies with neutralizing and nonneutralizing antibodies are consistent with the EM images; cleaved, SOSIP-stabilized trimers express quaternary structure-dependent epitopes, whereas uncleaved trimers expose nonneutralizing gp120 and gp41ECTO epitopes that are occluded on cleaved trimers. These findings have adverse implications for using soluble, uncleaved trimers for structural studies, and the rationale for testing uncleaved trimers as vaccine candidates also needs to be reevaluated.
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http://dx.doi.org/10.1073/pnas.1314351110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3831437PMC
November 2013
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