Publications by authors named "Christopher O Barnes"

42 Publications

Broad cross-reactivity across sarbecoviruses exhibited by a subset of COVID-19 donor-derived neutralizing antibodies.

bioRxiv 2021 Apr 26. Epub 2021 Apr 26.

Many anti-SARS-CoV-2 neutralizing antibodies target the ACE2-binding site on viral spike receptor-binding domains (RBDs). The most potent antibodies recognize exposed variable epitopes, often rendering them ineffective against other sarbecoviruses and SARS-CoV-2 variants. Class 4 anti-RBD antibodies against a less-exposed, but more-conserved, cryptic epitope could recognize newly-emergent zoonotic sarbecoviruses and variants, but usually show only weak neutralization potencies. We characterized two class 4 anti-RBD antibodies derived from COVID-19 donors that exhibited broad recognition and potent neutralization of zoonotic coronavirus and SARS-CoV-2 variants. C118-RBD and C022-RBD structures revealed CDRH3 mainchain H-bond interactions that extended an RBD β-sheet, thus reducing sensitivity to RBD sidechain changes, and epitopes that extended from the cryptic epitope to occlude ACE2 binding. A C118-spike trimer structure revealed rotated RBDs to allow cryptic epitope access and the potential for intra-spike crosslinking to increase avidity. These studies facilitate vaccine design and illustrate potential advantages of class 4 RBD-binding antibody therapeutics.
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http://dx.doi.org/10.1101/2021.04.23.441195DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8095199PMC
April 2021

Detection and characterization of the SARS-CoV-2 lineage B.1.526 in New York.

bioRxiv 2021 Apr 22. Epub 2021 Apr 22.

Wide-scale SARS-CoV-2 genome sequencing is critical to tracking viral evolution during the ongoing pandemic. Variants first detected in the United Kingdom, South Africa, and Brazil have spread to multiple countries. We developed the software tool, Variant Database (VDB), for quickly examining the changing landscape of spike mutations. Using VDB, we detected an emerging lineage of SARS-CoV-2 in the New York region that shares mutations with previously reported variants. The most common sets of spike mutations in this lineage (now designated as B.1.526) are L5F, T95I, D253G, E484K or S477N, D614G, and A701V. This lineage was first sequenced in late November 2020 when it represented <1% of sequenced coronavirus genomes that were collected in New York City (NYC). By February 2021, genomes from this lineage accounted for 32% of 3288 sequenced genomes from NYC specimens. Phylodynamic inference confirmed the rapid growth of the B.1.526 lineage in NYC, notably the sub-clade defined by the spike mutation E484K, which has outpaced the growth of other variants in NYC. Pseudovirus neutralization experiments demonstrated that B.1.526 spike mutations adversely affect the neutralization titer of convalescent and vaccinee plasma, indicating the public health importance of this lineage.
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http://dx.doi.org/10.1101/2021.02.14.431043DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8077570PMC
April 2021

Cryo-EM structures of HIV-1 trimer bound to CD4-mimetics BNM-III-170 and M48U1 adopt a CD4-bound open conformation.

Nat Commun 2021 03 29;12(1):1950. Epub 2021 Mar 29.

Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA.

Human immunodeficiency virus-1 (HIV-1), the causative agent of AIDS, impacts millions of people. Entry into target cells is mediated by the HIV-1 envelope (Env) glycoprotein interacting with host receptor CD4, which triggers conformational changes allowing binding to a coreceptor and subsequent membrane fusion. Small molecule or peptide CD4-mimetic drugs mimic CD4's Phe43 interaction with Env by inserting into the conserved Phe43 pocket on Env subunit gp120. Here, we present single-particle cryo-EM structures of CD4-mimetics BNM-III-170 and M48U1 bound to a BG505 native-like Env trimer plus the CD4-induced antibody 17b at 3.7 Å and 3.9 Å resolution, respectively. CD4-mimetic-bound BG505 exhibits canonical CD4-induced conformational changes including trimer opening, formation of the 4-stranded gp120 bridging sheet, displacement of the V1V2 loop, and formation of a compact and elongated gp41 HR1C helical bundle. We conclude that CD4-induced structural changes on both gp120 and gp41 Env subunits are induced by binding to the gp120 Phe43 pocket.
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http://dx.doi.org/10.1038/s41467-021-21816-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8007822PMC
March 2021

Bispecific IgG neutralizes SARS-CoV-2 variants and prevents escape in mice.

Nature 2021 Mar 25. Epub 2021 Mar 25.

European Commission, Joint Research Centre, Ispra, Italy.

Neutralizing antibodies that target the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein are among the most promising approaches against COVID-19. A bispecific IgG1-like molecule (CoV-X2) has been developed on the basis of C121 and C135, two antibodies derived from donors who had recovered from COVID-19. Here we show that CoV-X2 simultaneously binds two independent sites on the RBD and, unlike its parental antibodies, prevents detectable spike binding to the cellular receptor of the virus, angiotensin-converting enzyme 2 (ACE2). Furthermore, CoV-X2 neutralizes wild-type SARS-CoV-2 and its variants of concern, as well as escape mutants generated by the parental monoclonal antibodies. We also found that in a mouse model of SARS-CoV-2 infection with lung inflammation, CoV-X2 protects mice from disease and suppresses viral escape. Thus, the simultaneous targeting of non-overlapping RBD epitopes by IgG-like bispecific antibodies is feasible and effective, and combines the advantages of antibody cocktails with those of single-molecule approaches.
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http://dx.doi.org/10.1038/s41586-021-03461-yDOI Listing
March 2021

Development of potency, breadth and resilience to viral escape mutations in SARS-CoV-2 neutralizing antibodies.

bioRxiv 2021 Mar 8. Epub 2021 Mar 8.

Antibodies elicited in response to infection undergo somatic mutation in germinal centers that can result in higher affinity for the cognate antigen. To determine the effects of somatic mutation on the properties of SARS-CoV-2 spike receptor-binding domain (RBD)-specific antibodies, we analyzed six independent antibody lineages. As well as increased neutralization potency, antibody evolution changed pathways for acquisition of resistance and, in some cases, restricted the range of neutralization escape options. For some antibodies, maturation apparently imposed a requirement for multiple spike mutations to enable escape. For certain antibody lineages, maturation enabled neutralization of circulating SARS-CoV-2 variants of concern and heterologous sarbecoviruses. Antibody-antigen structures revealed that these properties resulted from substitutions that allowed additional variability at the interface with the RBD. These findings suggest that increasing antibody diversity through prolonged or repeated antigen exposure may improve protection against diversifying SARS-CoV-2 populations, and perhaps against other pandemic threat coronaviruses.
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http://dx.doi.org/10.1101/2021.03.07.434227DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7987023PMC
March 2021

Mutational escape from the polyclonal antibody response to SARS-CoV-2 infection is largely shaped by a single class of antibodies.

bioRxiv 2021 Mar 18. Epub 2021 Mar 18.

Monoclonal antibodies targeting a variety of epitopes have been isolated from individuals previously infected with SARS-CoV-2, but the relative contributions of these different antibody classes to the polyclonal response remains unclear. Here we use a yeast-display system to map all mutations to the viral spike receptor-binding domain (RBD) that escape binding by representatives of three potently neutralizing classes of anti-RBD antibodies with high-resolution structures. We compare the antibody-escape maps to similar maps for convalescent polyclonal plasma, including plasma from individuals from whom some of the antibodies were isolated. The plasma-escape maps most closely resemble those of a single class of antibodies that target an epitope on the RBD that includes site E484. Therefore, although the human immune system can produce antibodies that target diverse RBD epitopes, in practice the polyclonal response to infection is dominated by a single class of antibodies targeting an epitope that is already undergoing rapid evolution.
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http://dx.doi.org/10.1101/2021.03.17.435863DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7987015PMC
March 2021

mRNA vaccine-elicited antibodies to SARS-CoV-2 and circulating variants.

Nature 2021 04 10;592(7855):616-622. Epub 2021 Feb 10.

Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA.

Here we report on the antibody and memory B cell responses of a cohort of 20 volunteers who received the Moderna (mRNA-1273) or Pfizer-BioNTech (BNT162b2) vaccine against SARS-CoV-2. Eight weeks after the second injection of vaccine, volunteers showed high levels of IgM and IgG anti-SARS-CoV-2 spike protein (S) and receptor-binding-domain (RBD) binding titre. Moreover, the plasma neutralizing activity and relative numbers of RBD-specific memory B cells of vaccinated volunteers were equivalent to those of individuals who had recovered from natural infection. However, activity against SARS-CoV-2 variants that encode E484K-, N501Y- or K417N/E484K/N501-mutant S was reduced by a small-but significant-margin. The monoclonal antibodies elicited by the vaccines potently neutralize SARS-CoV-2, and target a number of different RBD epitopes in common with monoclonal antibodies isolated from infected donors. However, neutralization by 14 of the 17 most-potent monoclonal antibodies that we tested was reduced or abolished by the K417N, E484K or N501Y mutation. Notably, these mutations were selected when we cultured recombinant vesicular stomatitis virus expressing SARS-CoV-2 S in the presence of the monoclonal antibodies elicited by the vaccines. Together, these results suggest that the monoclonal antibodies in clinical use should be tested against newly arising variants, and that mRNA vaccines may need to be updated periodically to avoid a potential loss of clinical efficacy.
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http://dx.doi.org/10.1038/s41586-021-03324-6DOI Listing
April 2021

mRNA vaccine-elicited antibodies to SARS-CoV-2 and circulating variants.

bioRxiv 2021 Jan 19. Epub 2021 Jan 19.

To date severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has infected nearly 100 million individuals resulting in over two million deaths. Many vaccines are being deployed to prevent coronavirus disease-2019 (COVID-19) including two novel mRNA-based vaccines . These vaccines elicit neutralizing antibodies and appear to be safe and effective, but the precise nature of the elicited antibodies is not known . Here we report on the antibody and memory B cell responses in a cohort of 20 volunteers who received either the Moderna (mRNA-1273) or Pfizer-BioNTech (BNT162b2) vaccines. Consistent with prior reports, 8 weeks after the second vaccine injection volunteers showed high levels of IgM, and IgG anti-SARS-CoV-2 spike protein (S), receptor binding domain (RBD) binding titers . Moreover, the plasma neutralizing activity, and the relative numbers of RBD-specific memory B cells were equivalent to individuals who recovered from natural infection . However, activity against SARS-CoV-2 variants encoding E484K or N501Y or the K417N:E484K:N501Y combination was reduced by a small but significant margin. Consistent with these findings, vaccine-elicited monoclonal antibodies (mAbs) potently neutralize SARS-CoV-2, targeting a number of different RBD epitopes epitopes in common with mAbs isolated from infected donors. Structural analyses of mAbs complexed with S trimer suggest that vaccine- and virus-encoded S adopts similar conformations to induce equivalent anti-RBD antibodies. However, neutralization by 14 of the 17 most potent mAbs tested was reduced or abolished by either K417N, or E484K, or N501Y mutations. Notably, the same mutations were selected when recombinant vesicular stomatitis virus (rVSV)/SARS-CoV-2 S was cultured in the presence of the vaccine elicited mAbs. Taken together the results suggest that the monoclonal antibodies in clinical use should be tested against newly arising variants, and that mRNA vaccines may need to be updated periodically to avoid potential loss of clinical efficacy.
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http://dx.doi.org/10.1101/2021.01.15.426911DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7836122PMC
January 2021

Bispecific antibody prevents SARS-CoV-2 escape and protects mice from disease.

bioRxiv 2021 Jan 22. Epub 2021 Jan 22.

Neutralizing antibodies targeting the receptor binding domain (RBD) of the SARS-CoV-2 Spike (S) are among the most promising approaches against coronavirus disease 2019 (COVID-19) . We developed a bispecific, IgG1-like molecule based on two antibodies derived from COVID-19 convalescent donors, C121 and C135 . CoV-X2 simultaneously binds two independent sites on the RBD and, unlike its parental antibodies, completely prevents S binding to Angiotensin-Converting Enzyme 2 (ACE2), the virus cellular receptor. Furthermore, CoV-X2 recognizes a broad panel of RBD variants and neutralizes SARS-CoV-2 and the escape mutants generated by the single monoclonals at sub-nanomolar concentrations. In a novel model of SARS-CoV-2 infection with lung inflammation, CoV-X2 protects mice from disease and suppresses viral escape. Thus, simultaneous targeting of non-overlapping RBD epitopes by IgG-like bispecific antibodies is feasible and effective, combining into a single molecule the advantages of antibody cocktails.
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http://dx.doi.org/10.1101/2021.01.22.427567DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7836104PMC
January 2021

Evolution of antibody immunity to SARS-CoV-2.

Nature 2021 03 18;591(7851):639-644. Epub 2021 Jan 18.

Laboratory of Molecular Immunology, The Rockefeller University, New York, NY, USA.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has infected 78 million individuals and is responsible for over 1.7 million deaths to date. Infection is associated with the development of variable levels of antibodies with neutralizing activity, which can protect against infection in animal models. Antibody levels decrease with time, but, to our knowledge, the nature and quality of the memory B cells that would be required to produce antibodies upon reinfection has not been examined. Here we report on the humoral memory response in a cohort of 87 individuals assessed at 1.3 and 6.2 months after infection with SARS-CoV-2. We find that titres of IgM and IgG antibodies against the receptor-binding domain (RBD) of the spike protein of SARS-CoV-2 decrease significantly over this time period, with IgA being less affected. Concurrently, neutralizing activity in plasma decreases by fivefold in pseudotype virus assays. By contrast, the number of RBD-specific memory B cells remains unchanged at 6.2 months after infection. Memory B cells display clonal turnover after 6.2 months, and the antibodies that they express have greater somatic hypermutation, resistance to RBD mutations and increased potency, indicative of continued evolution of the humoral response. Immunofluorescence and PCR analyses of intestinal biopsies obtained from asymptomatic individuals at 4 months after the onset of coronavirus disease 2019 (COVID-19) revealed the persistence of SARS-CoV-2 nucleic acids and immunoreactivity in the small bowel of 7 out of 14 individuals. We conclude that the memory B cell response to SARS-CoV-2 evolves between 1.3 and 6.2 months after infection in a manner that is consistent with antigen persistence.
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http://dx.doi.org/10.1038/s41586-021-03207-wDOI Listing
March 2021

Structural biology in the fight against COVID-19.

Nat Struct Mol Biol 2021 01;28(1):2-7

Center for Infectious Disease Research, Westlake Laboratory of Life Sciences and Biomedicine, Key Laboratory of Structural Biology of Zhejiang Province, School of Life Sciences, Westlake University, Hangzhou, China.

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http://dx.doi.org/10.1038/s41594-020-00544-8DOI Listing
January 2021

Mosaic nanoparticles elicit cross-reactive immune responses to zoonotic coronaviruses in mice.

Science 2021 02 12;371(6530):735-741. Epub 2021 Jan 12.

Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA.

Protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and SARS-related emergent zoonotic coronaviruses is urgently needed. We made homotypic nanoparticles displaying the receptor binding domain (RBD) of SARS-CoV-2 or co-displaying SARS-CoV-2 RBD along with RBDs from animal betacoronaviruses that represent threats to humans (mosaic nanoparticles with four to eight distinct RBDs). Mice immunized with RBD nanoparticles, but not soluble antigen, elicited cross-reactive binding and neutralization responses. Mosaic RBD nanoparticles elicited antibodies with superior cross-reactive recognition of heterologous RBDs relative to sera from immunizations with homotypic SARS-CoV-2-RBD nanoparticles or COVID-19 convalescent human plasmas. Moreover, after priming, sera from mosaic RBD-immunized mice neutralized heterologous pseudotyped coronaviruses as well as or better than sera from homotypic SARS-CoV-2-RBD nanoparticle immunizations, demonstrating no loss of immunogenicity against particular RBDs resulting from co-display. A single immunization with mosaic RBD nanoparticles provides a potential strategy to simultaneously protect against SARS-CoV-2 and emerging zoonotic coronaviruses.
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http://dx.doi.org/10.1126/science.abf6840DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7928838PMC
February 2021

Mosaic RBD nanoparticles elicit neutralizing antibodies against SARS-CoV-2 and zoonotic coronaviruses.

bioRxiv 2020 Nov 17. Epub 2020 Nov 17.

Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA.

Protection against SARS-CoV-2 and SARS-related zoonotic coronaviruses with pandemic potential is urgently needed. To evaluate immunization strategies, we made nanoparticles displaying the receptor-binding domain (RBD) of only SARS-CoV-2 (homotypic nanoparticles) or co-displaying the SARS-CoV-2 RBD along with RBDs from animal betacoronaviruses that represent threats to humans (mosaic nanoparticles; 4-8 distinct RBDs). Mice immunized with RBD-nanoparticles, but not soluble antigen, elicited cross-reactive antibody binding and neutralization responses, confirming increased immunogenicity from multimerization. Mosaic-RBD-nanoparticles elicited antibodies with superior cross-reactive recognition of heterologous RBDs compared to sera from immunizations with homotypic SARS-CoV-2-RBD-nanoparticles or antibodies from COVID-19 convalescent human plasmas. Moreover, sera from mosaic-RBD- immunized mice neutralized heterologous pseudotyped coronaviruses equivalently or better after priming than sera from homotypic SARS-CoV-2-RBD-nanoparticle immunizations, demonstrating no loss of immunogenicity against any particular RBD resulting from co-display. Thus, a single immunization with mosaic-RBD-nanoparticles provides a potential strategy to simultaneously protect against SARS-CoV-2 and emerging zoonotic coronaviruses.
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http://dx.doi.org/10.1101/2020.11.17.387092DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7685334PMC
November 2020

Evolution of Antibody Immunity to SARS-CoV-2.

bioRxiv 2020 Nov 5. Epub 2020 Nov 5.

SARS-CoV-2 has infected 47 million individuals and is responsible for over 1.2 million deaths to date. Infection is associated with development of variable levels of antibodies with neutralizing activity that can protect against infection in animal models. Antibody levels decrease with time, but the nature and quality of the memory B cells that would be called upon to produce antibodies upon re-infection has not been examined. Here we report on the humoral memory response in a cohort of 87 individuals assessed at 1.3 and 6.2 months after infection. We find that IgM, and IgG anti-SARS-CoV-2 spike protein receptor binding domain (RBD) antibody titers decrease significantly with IgA being less affected. Concurrently, neutralizing activity in plasma decreases by five-fold in pseudotype virus assays. In contrast, the number of RBD-specific memory B cells is unchanged. Memory B cells display clonal turnover after 6.2 months, and the antibodies they express have greater somatic hypermutation, increased potency and resistance to RBD mutations, indicative of continued evolution of the humoral response. Analysis of intestinal biopsies obtained from asymptomatic individuals 3 months after COVID-19 onset, using immunofluorescence, electron tomography or polymerase chain reaction, revealed persistence of SARS-CoV-2 in the small bowel of 7 out of 14 volunteers. We conclude that the memory B cell response to SARS-CoV-2 evolves between 1.3 and 6.2 months after infection in a manner that is consistent with antigen persistence.
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http://dx.doi.org/10.1101/2020.11.03.367391DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7654855PMC
November 2020

De novo design of potent and resilient hACE2 decoys to neutralize SARS-CoV-2.

Science 2020 12 5;370(6521):1208-1214. Epub 2020 Nov 5.

Neoleukin Therapeutics Inc., Seattle, WA, USA.

We developed a de novo protein design strategy to swiftly engineer decoys for neutralizing pathogens that exploit extracellular host proteins to infect the cell. Our pipeline allowed the design, validation, and optimization of de novo human angiotensin-converting enzyme 2 (hACE2) decoys to neutralize severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The best monovalent decoy, CTC-445.2, bound with low nanomolar affinity and high specificity to the receptor-binding domain (RBD) of the spike protein. Cryo-electron microscopy (cryo-EM) showed that the design is accurate and can simultaneously bind to all three RBDs of a single spike protein. Because the decoy replicates the spike protein target interface in hACE2, it is intrinsically resilient to viral mutational escape. A bivalent decoy, CTC-445.2d, showed ~10-fold improvement in binding. CTC-445.2d potently neutralized SARS-CoV-2 infection of cells in vitro, and a single intranasal prophylactic dose of decoy protected Syrian hamsters from a subsequent lethal SARS-CoV-2 challenge.
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http://dx.doi.org/10.1126/science.abe0075DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7920261PMC
December 2020

A broadly neutralizing macaque monoclonal antibody against the HIV-1 V3-Glycan patch.

Elife 2020 10 21;9. Epub 2020 Oct 21.

Laboratory of Molecular Immunology, The Rockefeller University, New York, United States.

A small fraction of HIV-1- infected humans develop broadly neutralizing antibodies (bNAbs) against HIV-1 that protect macaques from simian immunodeficiency HIV chimeric virus (SHIV). Similarly, a small number of macaques infected with SHIVs develop broadly neutralizing serologic activity, but less is known about the nature of simian antibodies. Here, we report on a monoclonal antibody, Ab1485, isolated from a macaque infected with SHIVAD8 that developed broadly neutralizing serologic activity targeting the V3-glycan region of HIV-1 Env. Ab1485 neutralizes 38.1% of HIV-1 isolates in a 42-pseudovirus panel with a geometric mean IC50 of 0.055 µg/mLl and SHIVAD8 with an IC50 of 0.028 µg/mLl. Ab1485 binds the V3-glycan epitope in a glycan-dependent manner. A 3.5 Å cryo-electron microscopy structure of Ab1485 in complex with a native-like SOSIP Env trimer showed conserved contacts with the N332gp120 glycan and gp120 GDIR peptide motif, but in a distinct Env-binding orientation relative to human V3/N332gp120 glycan-targeting bNAbs. Intravenous infusion of Ab1485 protected macaques from a high dose challenge with SHIVAD8. We conclude that macaques can develop bNAbs against the V3-glycan patch that resemble human V3-glycan bNAbs.
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http://dx.doi.org/10.7554/eLife.61991DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7577740PMC
October 2020

SARS-CoV-2 neutralizing antibody structures inform therapeutic strategies.

Nature 2020 12 12;588(7839):682-687. Epub 2020 Oct 12.

Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA.

The coronavirus disease 2019 (COVID-19) pandemic presents an urgent health crisis. Human neutralizing antibodies that target the host ACE2 receptor-binding domain (RBD) of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) spike protein show promise therapeutically and are being evaluated clinically. Here, to identify the structural correlates of SARS-CoV-2 neutralization, we solved eight new structures of distinct COVID-19 human neutralizing antibodies in complex with the SARS-CoV-2 spike trimer or RBD. Structural comparisons allowed us to classify the antibodies into categories: (1) neutralizing antibodies encoded by the VH3-53 gene segment with short CDRH3 loops that block ACE2 and bind only to 'up' RBDs; (2) ACE2-blocking neutralizing antibodies that bind both up and 'down' RBDs and can contact adjacent RBDs; (3) neutralizing antibodies that bind outside the ACE2 site and recognize both up and down RBDs; and (4) previously described antibodies that do not block ACE2 and bind only to up RBDs. Class 2 contained four neutralizing antibodies with epitopes that bridged RBDs, including a VH3-53 antibody that used a long CDRH3 with a hydrophobic tip to bridge between adjacent down RBDs, thereby locking the spike into a closed conformation. Epitope and paratope mapping revealed few interactions with host-derived N-glycans and minor contributions of antibody somatic hypermutations to epitope contacts. Affinity measurements and mapping of naturally occurring and in vitro-selected spike mutants in 3D provided insight into the potential for SARS-CoV-2 to escape from antibodies elicited during infection or delivered therapeutically. These classifications and structural analyses provide rules for assigning current and future human RBD-targeting antibodies into classes, evaluating avidity effects and suggesting combinations for clinical use, and provide insight into immune responses against SARS-CoV-2.
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http://dx.doi.org/10.1038/s41586-020-2852-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8092461PMC
December 2020

Structural classification of neutralizing antibodies against the SARS-CoV-2 spike receptor-binding domain suggests vaccine and therapeutic strategies.

bioRxiv 2020 Aug 30. Epub 2020 Aug 30.

The COVID-19 pandemic presents an urgent health crisis. Human neutralizing antibodies (hNAbs) that target the host ACE2 receptor-binding domain (RBD) of the SARS-CoV-2 spike show therapeutic promise and are being evaluated clincally . To determine structural correlates of SARS-CoV-2 neutralization, we solved 8 new structures of distinct COVID-19 hNAbs in complex with SARS-CoV-2 spike trimer or RBD. Structural comparisons allowed classification into categories: (1) VH3-53 hNAbs with short CDRH3s that block ACE2 and bind only to up RBDs, (2) ACE2-blocking hNAbs that bind both up and down RBDs and can contact adjacent RBDs, (3) hNAbs that bind outside the ACE2 site and recognize up and down RBDs, and (4) Previously-described antibodies that do not block ACE2 and bind only up RBDs . Class 2 comprised four hNAbs whose epitopes bridged RBDs, including a VH3-53 hNAb that used a long CDRH3 with a hydrophobic tip to bridge between adjacent down RBDs, thereby locking spike into a closed conformation. Epitope/paratope mapping revealed few interactions with host-derived N-glycans and minor contributions of antibody somatic hypermutations to epitope contacts. Affinity measurements and mapping of naturally-occurring and in vitro-selected spike mutants in 3D provided insight into the potential for SARS-CoV-2 escape from antibodies elicited during infection or delivered therapeutically. These classifications and structural analyses provide rules for assigning current and future human RBD-targeting antibodies into classes, evaluating avidity effects, suggesting combinations for clinical use, and providing insight into immune responses against SARS-CoV-2.
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http://dx.doi.org/10.1101/2020.08.30.273920DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7457611PMC
August 2020

Structures of Human Antibodies Bound to SARS-CoV-2 Spike Reveal Common Epitopes and Recurrent Features of Antibodies.

Cell 2020 08 24;182(4):828-842.e16. Epub 2020 Jun 24.

Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA. Electronic address:

Neutralizing antibody responses to coronaviruses mainly target the receptor-binding domain (RBD) of the trimeric spike. Here, we characterized polyclonal immunoglobulin Gs (IgGs) and Fabs from COVID-19 convalescent individuals for recognition of coronavirus spikes. Plasma IgGs differed in their focus on RBD epitopes, recognition of alpha- and beta-coronaviruses, and contributions of avidity to increased binding/neutralization of IgGs over Fabs. Using electron microscopy, we examined specificities of polyclonal plasma Fabs, revealing recognition of both S1 and RBD epitopes on SARS-CoV-2 spike. Moreover, a 3.4 Å cryo-electron microscopy (cryo-EM) structure of a neutralizing monoclonal Fab-spike complex revealed an epitope that blocks ACE2 receptor binding. Modeling based on these structures suggested different potentials for inter-spike crosslinking by IgGs on viruses, and characterized IgGs would not be affected by identified SARS-CoV-2 spike mutations. Overall, our studies structurally define a recurrent anti-SARS-CoV-2 antibody class derived from VH3-53/VH3-66 and similarity to a SARS-CoV VH3-30 antibody, providing criteria for evaluating vaccine-elicited antibodies.
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http://dx.doi.org/10.1016/j.cell.2020.06.025DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7311918PMC
August 2020

Structures of human antibodies bound to SARS-CoV-2 spike reveal common epitopes and recurrent features of antibodies.

bioRxiv 2020 May 29. Epub 2020 May 29.

Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA.

Neutralizing antibody responses to coronaviruses focus on the trimeric spike, with most against the receptor-binding domain (RBD). Here we characterized polyclonal IgGs and Fabs from COVID-19 convalescent individuals for recognition of coronavirus spikes. Plasma IgGs differed in their degree of focus on RBD epitopes, recognition of SARS-CoV, MERS-CoV, and mild coronaviruses, and how avidity effects contributed to increased binding/neutralization of IgGs over Fabs. Electron microscopy reconstructions of polyclonal plasma Fab-spike complexes showed recognition of both S1 and RBD epitopes. A 3.4Å cryo-EM structure of a neutralizing monoclonal Fab-S complex revealed an epitope that blocks ACE2 receptor-binding on "up" RBDs. Modeling suggested that IgGs targeting these sites have different potentials for inter-spike crosslinking on viruses and would not be greatly affected by identified SARS-CoV-2 spike mutations. These studies structurally define a recurrent anti-SARS-CoV-2 antibody class derived from and similarity to a SARS-CoV antibody, providing criteria for evaluating vaccine-elicited antibodies.
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http://dx.doi.org/10.1101/2020.05.28.121533DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7302198PMC
May 2020

Convergent antibody responses to SARS-CoV-2 in convalescent individuals.

Nature 2020 08 18;584(7821):437-442. Epub 2020 Jun 18.

Laboratory of Molecular Immunology, The Rockefeller University, New York, NY, USA.

During the coronavirus disease-2019 (COVID-19) pandemic, severe acute respiratory syndrome-related coronavirus-2 (SARS-CoV-2) has led to the infection of millions of people and has claimed hundreds of thousands of lives. The entry of the virus into cells depends on the receptor-binding domain (RBD) of the spike (S) protein of SARS-CoV-2. Although there is currently no vaccine, it is likely that antibodies will be essential for protection. However, little is known about the human antibody response to SARS-CoV-2. Here we report on 149 COVID-19-convalescent individuals. Plasma samples collected an average of 39 days after the onset of symptoms had variable half-maximal pseudovirus neutralizing titres; titres were less than 50 in 33% of samples, below 1,000 in 79% of samples and only 1% of samples had titres above 5,000. Antibody sequencing revealed the expansion of clones of RBD-specific memory B cells that expressed closely related antibodies in different individuals. Despite low plasma titres, antibodies to three distinct epitopes on the RBD neutralized the virus with half-maximal inhibitory concentrations (IC values) as low as 2 ng ml. In conclusion, most convalescent plasma samples obtained from individuals who recover from COVID-19 do not contain high levels of neutralizing activity. Nevertheless, rare but recurring RBD-specific antibodies with potent antiviral activity were found in all individuals tested, suggesting that a vaccine designed to elicit such antibodies could be broadly effective.
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http://dx.doi.org/10.1038/s41586-020-2456-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7442695PMC
August 2020

Convergent Antibody Responses to SARS-CoV-2 Infection in Convalescent Individuals.

bioRxiv 2020 May 22. Epub 2020 May 22.

Laboratory of Molecular Immunology, The Rockefeller University, New York, NY 10065, USA.

During the COVID-19 pandemic, SARS-CoV-2 infected millions of people and claimed hundreds of thousands of lives. Virus entry into cells depends on the receptor binding domain (RBD) of the SARS-CoV-2 spike protein (S). Although there is no vaccine, it is likely that antibodies will be essential for protection. However, little is known about the human antibody response to SARS-CoV-2. Here we report on 149 COVID-19 convalescent individuals. Plasmas collected an average of 39 days after the onset of symptoms had variable half-maximal neutralizing titers ranging from undetectable in 33% to below 1:1000 in 79%, while only 1% showed titers >1:5000. Antibody cloning revealed expanded clones of RBD-specific memory B cells expressing closely related antibodies in different individuals. Despite low plasma titers, antibodies to three distinct epitopes on RBD neutralized at half-maximal inhibitory concentrations (ICs) as low as single digit ng/mL. Thus, most convalescent plasmas obtained from individuals who recover from COVID-19 do not contain high levels of neutralizing activity. Nevertheless, rare but recurring RBD-specific antibodies with potent antiviral activity were found in all individuals tested, suggesting that a vaccine designed to elicit such antibodies could be broadly effective.
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http://dx.doi.org/10.1101/2020.05.13.092619DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7263513PMC
May 2020

Restriction of HIV-1 Escape by a Highly Broad and Potent Neutralizing Antibody.

Cell 2020 02 30;180(3):471-489.e22. Epub 2020 Jan 30.

Laboratory of Experimental Immunology, Institute of Virology, Faculty of Medicine and University Hospital Cologne, University of Cologne, 50931 Cologne, Germany; German Center for Infection Research (DZIF), partner site Bonn-Cologne, 50931 Cologne, Germany; Center for Molecular Medicine Cologne (CMMC), University of Cologne, 50931 Cologne, Germany. Electronic address:

Broadly neutralizing antibodies (bNAbs) represent a promising approach to prevent and treat HIV-1 infection. However, viral escape through mutation of the HIV-1 envelope glycoprotein (Env) limits clinical applications. Here we describe 1-18, a new V1-46-encoded CD4 binding site (CD4bs) bNAb with outstanding breadth (97%) and potency (GeoMean IC = 0.048 μg/mL). Notably, 1-18 is not susceptible to typical CD4bs escape mutations and effectively overcomes HIV-1 resistance to other CD4bs bNAbs. Moreover, mutational antigenic profiling uncovered restricted pathways of HIV-1 escape. Of most promise for therapeutic use, even 1-18 alone fully suppressed viremia in HIV-1-infected humanized mice without selecting for resistant viral variants. A 2.5-Å cryo-EM structure of a 1-18-BG505 Env complex revealed that these characteristics are likely facilitated by a heavy-chain insertion and increased inter-protomer contacts. The ability of 1-18 to effectively restrict HIV-1 escape pathways provides a new option to successfully prevent and treat HIV-1 infection.
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http://dx.doi.org/10.1016/j.cell.2020.01.010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7042716PMC
February 2020

Immunization expands B cells specific to HIV-1 V3 glycan in mice and macaques.

Nature 2019 06 29;570(7762):468-473. Epub 2019 May 29.

Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA.

Broadly neutralizing monoclonal antibodies protect against infection with HIV-1 in animal models, suggesting that a vaccine that elicits these antibodies would be protective in humans. However, it has not yet been possible to induce adequate serological responses by vaccination. Here, to activate B cells that express precursors of broadly neutralizing antibodies within polyclonal repertoires, we developed an immunogen, RC1, that facilitates the recognition of the variable loop 3 (V3)-glycan patch on the envelope protein of HIV-1. RC1 conceals non-conserved immunodominant regions by the addition of glycans and/or multimerization on virus-like particles. Immunization of mice, rabbits and rhesus macaques with RC1 elicited serological responses that targeted the V3-glycan patch. Antibody cloning and cryo-electron microscopy structures of antibody-envelope complexes confirmed that immunization with RC1 expands clones of B cells that carry the anti-V3-glycan patch antibodies, which resemble precursors of human broadly neutralizing antibodies. Thus, RC1 may be a suitable priming immunogen for sequential vaccination strategies in the context of polyclonal repertoires.
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http://dx.doi.org/10.1038/s41586-019-1250-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6657810PMC
June 2019

Broad and Potent Neutralizing Antibodies Recognize the Silent Face of the HIV Envelope.

Immunity 2019 06 21;50(6):1513-1529.e9. Epub 2019 May 21.

Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA. Electronic address:

Broadly neutralizing antibodies (bNAbs) against HIV-1 envelope (Env) inform vaccine design and are potential therapeutic agents. We identified SF12 and related bNAbs with up to 62% neutralization breadth from an HIV-infected donor. SF12 recognized a glycan-dominated epitope on Env's silent face and was potent against clade AE viruses, which are poorly covered by V3-glycan bNAbs. A 3.3Å cryo-EM structure of a SF12-Env trimer complex showed additional contacts to Env protein residues by SF12 compared with VRC-PG05, the only other known donor-derived silentface antibody, explaining SF12's increased neutralization breadth, potency, and resistance to Env mutation routes. Asymmetric binding of SF12 was associated with distinct N-glycan conformations across Env protomers, demonstrating intra-Env glycan heterogeneity. Administrating SF12 to HIV-1-infected humanized mice suppressed viremia and selected for viruses lacking the N448 glycan. Effective bNAbs can therefore be raised against HIV-1 Env's silent face, suggesting their potential for HIV-1 prevention, therapy, and vaccine development.
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http://dx.doi.org/10.1016/j.immuni.2019.04.014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6591006PMC
June 2019

The crystal structure of dGTPase reveals the molecular basis of dGTP selectivity.

Proc Natl Acad Sci U S A 2019 05 24;116(19):9333-9339. Epub 2019 Apr 24.

Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260;

Deoxynucleotide triphosphohydrolases (dNTPases) play a critical role in cellular survival and DNA replication through the proper maintenance of cellular dNTP pools. While the vast majority of these enzymes display broad activity toward canonical dNTPs, such as the dNTPase SAMHD1 that blocks reverse transcription of retroviruses in macrophages by maintaining dNTP pools at low levels, ()dGTPase is the only known enzyme that specifically hydrolyzes dGTP. However, the mechanism behind dGTP selectivity is unclear. Here we present the free-, ligand (dGTP)- and inhibitor (GTP)-bound structures of hexameric dGTPase, including an X-ray free-electron laser structure of the free -dGTPase enzyme to 3.2 Å. To obtain this structure, we developed a method that applied UV-fluorescence microscopy, video analysis, and highly automated goniometer-based instrumentation to map and rapidly position individual crystals randomly located on fixed target holders, resulting in the highest indexing rates observed for a serial femtosecond crystallography experiment. Our structures show a highly dynamic active site where conformational changes are coupled to substrate (dGTP), but not inhibitor binding, since GTP locks dGTPase in its apo- form. Moreover, despite no sequence homology, -dGTPase and SAMHD1 share similar active-site and HD motif architectures; however, -dGTPase residues at the end of the substrate-binding pocket mimic Watson-Crick interactions providing guanine base specificity, while a 7-Å cleft separates SAMHD1 residues from dNTP bases, abolishing nucleotide-type discrimination. Furthermore, the structures shed light on the mechanism by which long distance binding (25 Å) of single-stranded DNA in an allosteric site primes the active site by conformationally "opening" a tyrosine gate allowing enhanced substrate binding.
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http://dx.doi.org/10.1073/pnas.1814999116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6511015PMC
May 2019

Partially Open HIV-1 Envelope Structures Exhibit Conformational Changes Relevant for Coreceptor Binding and Fusion.

Cell Host Microbe 2018 10;24(4):579-592.e4

Division of Biology and Biological Engineering, California Institute of Technology, 1200 E. California Boulevard, Pasadena, CA 91125, USA. Electronic address:

HIV-1 Env, a trimer of gp120-gp41 heterodimers, mediates membrane fusion after binding host receptor CD4. Receptor binding displaces V1V2 loops from Env's apex, allowing coreceptor binding and opening Env to enable gp41-mediated fusion. We present 3.54 Å and 4.06 Å cryoelectron microscopy structures of partially open soluble native-like Env trimers (SOSIPs) bound to CD4. One structure, a complex with a coreceptor-mimicking antibody that binds both CD4 and gp120, stabilizes the displaced V1V2 and reveals its structure. Comparing partially and fully open Envs with closed Envs shows that gp41 rearrangements are independent of the CD4-induced rearrangements that result in V1V2 displacement and formation of a 4-stranded bridging sheet. These findings suggest ordered conformational changes before coreceptor binding: (1) gp120 opening inducing side-chain rearrangements and a compact gp41 central helix conformation, and (2) 4-stranded bridging-sheet formation and V1V2 displacement. These analyses illuminate potential receptor-induced Env changes and inform design of therapeutics disrupting viral entry.
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http://dx.doi.org/10.1016/j.chom.2018.09.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6185872PMC
October 2018

Structural characterization of a highly-potent V3-glycan broadly neutralizing antibody bound to natively-glycosylated HIV-1 envelope.

Nat Commun 2018 03 28;9(1):1251. Epub 2018 Mar 28.

Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, 91125, USA.

Broadly neutralizing antibodies (bNAbs) isolated from HIV-1-infected individuals inform HIV-1 vaccine design efforts. Developing bNAbs with increased efficacy requires understanding how antibodies interact with the native oligomannose and complex-type N-glycan shield that hides most protein epitopes on HIV-1 envelope (Env). Here we present crystal structures, including a 3.8-Å X-ray free electron laser dataset, of natively glycosylated Env trimers complexed with BG18, the most potent V3/N332 glycan-targeting bNAb reported to date. Our structures show conserved contacts mediated by common D gene-encoded residues with the N332 glycan and the gp120 GDIR peptide motif, but a distinct Env-binding orientation relative to PGT121/10-1074 bNAbs. BG18's binding orientation provides additional contacts with N392 and N386 glycans near the V3-loop base and engages protein components of the V1-loop. The BG18-natively-glycosylated Env structures facilitate understanding of bNAb-glycan interactions critical for using V3/N332 bNAbs therapeutically and targeting their epitope for immunogen design.
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http://dx.doi.org/10.1038/s41467-018-03632-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5871869PMC
March 2018

MicroED Structure of Au(p-MBA) at Subatomic Resolution Reveals a Twinned FCC Cluster.

J Phys Chem Lett 2017 Nov 31;8(22):5523-5530. Epub 2017 Oct 31.

Department of Structural Biology, University of Pittsburgh , Pittsburgh, Pennsylvania 15260, United States.

Solving the atomic structure of metallic clusters is fundamental to understanding their optical, electronic, and chemical properties. Herein we present the structure of the largest aqueous gold cluster, Au(p-MBA) (p-MBA: para-mercaptobenzoic acid), solved by electron micro-diffraction (MicroED) to subatomic resolution (0.85 Å) and by X-ray diffraction at atomic resolution (1.3 Å). The 146 gold atoms may be decomposed into two constituent sets consisting of 119 core and 27 peripheral atoms. The core atoms are organized in a twinned FCC structure, whereas the surface gold atoms follow a C rotational symmetry about an axis bisecting the twinning plane. The protective layer of 57 p-MBAs fully encloses the cluster and comprises bridging, monomeric, and dimeric staple motifs. Au(p-MBA) is the largest cluster observed exhibiting a bulk-like FCC structure as well as the smallest gold particle exhibiting a stacking fault.
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http://dx.doi.org/10.1021/acs.jpclett.7b02621DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5769702PMC
November 2017

An engineered transforming growth factor β (TGF-β) monomer that functions as a dominant negative to block TGF-β signaling.

J Biol Chem 2017 04 22;292(17):7173-7188. Epub 2017 Feb 22.

From the Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15260,

The transforming growth factor β isoforms, TGF-β1, -β2, and -β3, are small secreted homodimeric signaling proteins with essential roles in regulating the adaptive immune system and maintaining the extracellular matrix. However, dysregulation of the TGF-β pathway is responsible for promoting the progression of several human diseases, including cancer and fibrosis. Despite the known importance of TGF-βs in promoting disease progression, no inhibitors have been approved for use in humans. Herein, we describe an engineered TGF-β monomer, lacking the heel helix, a structural motif essential for binding the TGF-β type I receptor (TβRI) but dispensable for binding the other receptor required for TGF-β signaling, the TGF-β type II receptor (TβRII), as an alternative therapeutic modality for blocking TGF-β signaling in humans. As shown through binding studies and crystallography, the engineered monomer retained the same overall structure of native TGF-β monomers and bound TβRII in an identical manner. Cell-based luciferase assays showed that the engineered monomer functioned as a dominant negative to inhibit TGF-β signaling with a of 20-70 nm Investigation of the mechanism showed that the high affinity of the engineered monomer for TβRII, coupled with its reduced ability to non-covalently dimerize and its inability to bind and recruit TβRI, enabled it to bind endogenous TβRII but prevented it from binding and recruiting TβRI to form a signaling complex. Such engineered monomers provide a new avenue to probe and manipulate TGF-β signaling and may inform similar modifications of other TGF-β family members.
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http://dx.doi.org/10.1074/jbc.M116.768754DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5409485PMC
April 2017