Publications by authors named "Nobutaka Numoto"

28 Publications

  • Page 1 of 1

Cutinases from thermophilic bacteria (actinomycetes): From identification to functional and structural characterization.

Methods Enzymol 2021 4;648:159-185. Epub 2021 Feb 4.

Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, Kyoto, Japan. Electronic address:

Thermophilic cutinases are mainly obtained from thermophilic actinomycetes, and are categorized into two groups, i.e., those with higher (>70°C) or lower (<70°C) thermostabilities. The thermostabilities of cutinases are highly relevant to their ability to degrade polyethylene terephthalate (PET). Many crystal structures of thermophilic cutinases have been solved, showing that their overall backbone structures are identical, irrespective of their ability to hydrolyze PET. One of the unique properties of cutinases is that metal ion-binding on the enzyme's surface both elevates their melting temperatures and activates the enzyme. In this chapter, we introduce the methodology for the identification and cloning of thermophilic cutinases from actinomycetes. For detailed characterization of cutinases, we describe the approach to analyze the intricate dynamics of the enzyme, based on its crystal structures complexed with metal ions and model substrates using a combination of experimental and computational techniques.
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http://dx.doi.org/10.1016/bs.mie.2020.12.031DOI Listing
February 2021

Molecular interactions of the CTLA-4 cytoplasmic region with the phosphoinositide 3-kinase SH2 domains.

Mol Immunol 2021 03 30;131:51-59. Epub 2020 Dec 30.

Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, 1-5 Hangi-cho, Shimogamo, Sakyo-ku, Kyoto 606-8522, Japan. Electronic address:

During T-cell regulation, T-cell receptors and CD28 lead to signaling activation, while T-lymphocyte antigen 4 (CTLA-4) is known to lead to downregulation, similar to programmed cell death-1 (PD-1). In the cytoplasmic tails of CD28 and CTLA-4, phosphoinositide 3-kinase (PI3K) binds to the consensus sequence including phosphotyrosine via SH2 domains, N- and C-terminal SH2 domains (nSH2 and cSH2), of its regulatory subunit, p85. In this study, we determined the crystal structure of a CTLA-4-derived phosphopeptide in complex with a Cys-substituted mutant of cSH2, C656S/C659V/C670L, at a 1.1 Å resolution. Phosphotyrosine of the bound peptide is tightly accommodated by the residues Arg631, Arg649, Ser651, and Ser652, similar to the cSH2 wild-type recognition mode of CD28, as reported previously. Upon the Cys mutation, the cSH2 thermal stability increased while the CTLA-4 binding affinity slightly changed. The binding experiments also showed that the binding affinity of CTLA-4 by cSH2 was approximately two orders of magnitude lower than that of CD28. Similar to CD28 binding, the CTLA-4 binding affinity of nSH2 was lower than that of cSH2. The complex structure of nSH2 and CTLA-4 was modeled, and compared with the crystal structure of cSH2 mutant and CTLA-4. The difference in the binding affinity between CD28 and CTLA-4, along with the difference between nSH2 and cSH2, could be explained by the 3D structures, which would be closely correlated with the respective T-cell signaling.
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http://dx.doi.org/10.1016/j.molimm.2020.12.002DOI Listing
March 2021

Lithocholic Acid Derivatives as Potent Vitamin D Receptor Agonists.

J Med Chem 2021 01 28;64(1):516-526. Epub 2020 Dec 28.

Department of Chemistry, Faculty of Science, Ochanomizu University, 2-1-1 Otsuka, Bunkyo-ku, Bunkyo, Tokyo 112-8610, Japan.

Lithocholic acid () was identified as a second endogenous ligand of vitamin D receptor (VDR), though its activity is very weak. In this study, we designed novel lithocholic acid derivatives based on the crystal structure of VDR-ligand-binding domain (LBD) bound to . Among the synthesized compounds, bearing a 2-hydroxy-2-methylprop-1-yl group instead of the 3-hydroxy group at the 3α-position of showed dramatically increased activity in HL-60 cell differentiation assay, being at least 10 000 times more potent than lithocholic acid () and 3 times more potent than 1α,25-dihydroxyvitamin D (). Although the binding affinities of and its epimer were less than that of , their transactivation activities were greater than that of . X-ray structure analyses of VDR LBD bound to or showed that the binding positions of these compounds in the ligand-binding pocket are similar to that of .
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http://dx.doi.org/10.1021/acs.jmedchem.0c01420DOI Listing
January 2021

Structural basis of mutants of PET-degrading enzyme from Saccharomonospora viridis AHK190 with high activity and thermal stability.

Proteins 2021 May 24;89(5):502-511. Epub 2020 Dec 24.

Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, Kyoto, Japan.

The cutinase-like enzyme from the thermophile Saccharomonospora viridis AHK190, Cut190, is a good candidate to depolymerize polyethylene terephthalate (PET) efficiently. We previously developed a mutant of Cut190 (S226P/R228S), which we designated as Cut190* that has both increased activity and stability and solved its crystal structure. Recently, we showed that mutation of D250C/E296C on one of the Ca -binding sites resulted in a higher thermal stability while retaining its polyesterase activity. In this study, we solved the crystal structures of Cut190* mutants, Q138A/D250C-E296C/Q123H/N202H, designated as Cut190*SS, and its inactive S176A mutant, Cut190*SS_S176A, at high resolution. The overall structures were similar to those of Cut190* and Cut190*S176A reported previously. As expected, Cys250 and Cys296 were closely located to form a disulfide bond, which would assuredly contribute to increase the stability. Isothermal titration calorimetry experiments and 3D Reference Interaction Site Model calculations showed that the metal-binding properties of the Cut190*SS series were different from those of the Cut190* series. However, our results show that binding of Ca to the weak binding site, site 1, would be retained, enabling Cut190*SS to keep its ability to use Ca to accelerate the conformational change from the closed (inactive) to the open (active) form. While increasing the thermal stability, Cut190*SS could still express its enzymatic function. Even after incubation at 70°C, which corresponds to the glass transition temperature of PET, the enzyme retained its activity well, implying a high applicability for industrial PET depolymerization using Cut190*SS.
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http://dx.doi.org/10.1002/prot.26034DOI Listing
May 2021

A Guillain-Barré syndrome-associated SIGLEC10 rare variant impairs its recognition of gangliosides.

J Autoimmun 2021 Jan 19;116:102571. Epub 2020 Nov 19.

Department of Immunology, Medical Research Institute, Tokyo Medical and Dental University, Tokyo, Japan. Electronic address:

Guillain-Barré syndrome (GBS), including its variant Miller Fisher syndrome (MFS), is an acute peripheral neuropathy that involves autoimmune mechanisms leading to the production of autoantibodies to gangliosides; sialic acid-containing glycosphingolipids. Although association with various genetic polymorphisms in the major histocompatibility complex (MHC) is shown in other autoimmune diseases, GBS is an exception, showing no such link. No significant association was found by genome wide association studies, suggesting that GBS is not associated with common variants. To address the involvement of rare variants in GBS, we analyzed Siglec-10, a sialic acid-recognizing inhibitory receptor expressed on B cells. Here we demonstrate that two rare variants encoding R47Q and A108V substitutions in the ligand-binding domain are significantly accumulated in patients with GBS. Because of strong linkage disequilibrium, there was no patient carrying only one of them. Recombinant Siglec-10 protein containing R47Q but not A108V shows impaired binding to gangliosides. Homology modeling revealed that the R47Q substitution causes marked alteration in the ligand-binding site. Thus, GBS is associated with a rare variant of the SIGLEC10 gene that impairs ligand binding of Siglec-10. Because Siglec-10 regulates antibody production to sialylated antigens, our finding suggests that Siglec-10 regulates development of GBS by suppressing antibody production to gangliosides, with defects in its function predisposing to disease.
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http://dx.doi.org/10.1016/j.jaut.2020.102571DOI Listing
January 2021

Multiple structural states of Ca2+-regulated PET hydrolase, Cut190, and its correlation with activity and stability.

J Biochem 2021 Mar;169(2):207-213

Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, 1-5 Hangi-cho, Shimogamo, Sakyo-ku, Kyoto, Kyoto 606-8522, Japan.

An enzyme, Cut190, from a thermophilic isolate, Saccharomonospora viridis AHK190 could depolymerize polyethylene terephthalate (PET). The catalytic activity and stability of Cut190 and its S226P/R228S mutant, Cut190*, are regulated by Ca2+ binding. We previously determined the crystal structures of the inactive mutant of Cut190*, Cut190*S176A, in complex with metal ions, Ca2+ and Zn2+, and substrates, monoethyl succinate and monoethyl adipate. In this study, we determined the crystal structures of another mutant of Cut190*, Cut190**, in which the three C-terminal residues of Cut190* are deleted, and the inactive mutant, Cut190**S176A, in complex with metal ions. In addition to the previously observed closed, open and engaged forms, we determined the ejecting form, which would allow the product to irreversibly dissociate, followed by proceeding to the next cycle of reaction. These multiple forms would be stable or sub-stable states of Cut190, regulated by Ca2+ binding, and would be closely correlated with the enzyme function. Upon the deletion of the C-terminal residues, we found that the thermal stability increased while retaining the activity. The increased stability could be applied for the protein engineering of Cut190 for PET depolymerization as it requires the reaction above the glass transition temperature of PET.
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http://dx.doi.org/10.1093/jb/mvaa102DOI Listing
March 2021

Three-dimensional structure of a high affinity anti-(4-hydroxy-3-nitrophenyl)acetyl antibody possessing a glycine residue at position 95 of the heavy chain.

Mol Immunol 2019 10 11;114:545-552. Epub 2019 Sep 11.

Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, 1-5 Hangi-cho, Shimogamo, Sakyo-ku, Kyoto, 606-8522, Japan. Electronic address:

Antibodies possessing high affinity and specificity are desired as therapeutic reagents and biosensor materials. Such antibodies are often obtained from immunized animals through the process referred to as affinity maturation where antibody affinity increases with time after immunization. Somatic hypermutation (SHM) was shown to be involved in this process; however, structural basis of affinity maturation has not well been understood yet. We analyzed the crystal structure of a high affinity anti-(4-hydroxy-3-nitrophenyl)acetyl antibody, C6, possessing Gly at position 95 of heavy chain and 17 amino acid replacements by SHM. Here, we discuss how the amino acid residues at position 95, introduced at a junction of V and D gene segments during gene-recombination, as well as those replaced by SHM contribute to increasing the affinity by comparing the C6 structure with that of a germline low affinity antibody, N1G9, possessing Tyr at position 95.
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http://dx.doi.org/10.1016/j.molimm.2019.09.001DOI Listing
October 2019

Structural and functional properties of Grb2 SH2 dimer in CD28 binding.

Biophys Physicobiol 2019 22;16:80-88. Epub 2019 Feb 22.

Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, Kyoto 606-8522, Japan.

Growth factor receptor-bound protein 2 (Grb2) is an adaptor protein that plays a critical role in cellular signal transduction. It contains a central Src homology 2 (SH2) domain flanked by two Src homology 3 (SH3) domains. Binding of Grb2 SH2 to the cytoplasmic region of CD28, phosphorylated Tyr (pY) containing the peptide motif pY-X-N-X, is required for costimulatory signaling in T cells. In this study, we purified the dimer and monomer forms of Grb2 SH2, respectively, and analyzed their structural and functional properties. Size exclusion chromatography analysis showed that both dimer and monomer exist as stable states. Thermal stability analysis using circular dichroism showed that the dimer mostly dissociates into the monomer around 50°C. CD28 binding experiments showed that the affinity of the dimer to the phosphopeptide was about three fold higher than that of the monomer, possibly due to the avidity effect. The present crystal structure analysis of Grb2 SH2 showed two forms; one is monomer at 1.15 Å resolution, which is currently the highest resolution analysis, and another is dimer at 2.00 Å resolution. In the dimer structure, the C-terminal region, comprising residues 123-152, was extended towards the adjacent molecule, in which Trp121 was the hinge residue. The stable dimer purified using size exclusion chromatography would be due to the C-terminal helix "swapping". In cases where a mutation caused Trp121 to be replaced by Ser in Grb2 SH2, this protein still formed dimers, but lost the ability to bind CD28.
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http://dx.doi.org/10.2142/biophysico.16.0_80DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6435016PMC
February 2019

Dual conformation of the ligand induces the partial agonistic activity of retinoid X receptor α (RXRα).

FEBS Lett 2019 01 21;593(2):242-250. Epub 2018 Dec 21.

Department of Chemistry, Rikkyo University, Tokyo, Japan.

1-[(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydronaphthalen-2-yl)amino]benzotriazole-5-carboxylic acid (CBt-PMN), a partial agonist of retinoid X receptor (RXR), has attracted attention due to its potential to treat type 2 diabetes and central nervous system diseases with reduced adverse effects of existing full agonists. Herein, we report the crystal structure of CBt-PMN-bound ligand-binding domain of human RXRα (hRXRα) and its biochemical characterization. Interestingly, the structure is a tetramer in nature, in which CBt-PMNs are clearly found binding in two different conformations. The dynamics of the hRXRα/CBt-PMN complex examined using molecular dynamics simulations suggest that the flexibility of the AF-2 interface depends on the conformation of the ligand. These facts reveal that the dual conformation of CBt-PMN in the complex is probably the reason behind its partial agonistic activity.
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http://dx.doi.org/10.1002/1873-3468.13301DOI Listing
January 2019

Structural Dynamics of the PET-Degrading Cutinase-like Enzyme from Saccharomonospora viridis AHK190 in Substrate-Bound States Elucidates the Ca-Driven Catalytic Cycle.

Biochemistry 2018 09 27;57(36):5289-5300. Epub 2018 Aug 27.

Graduate School of Life and Environmental Sciences , Kyoto Prefectural University , 1-5 Hangi-cho, Shimogamo , Sakyo-ku, Kyoto , Kyoto 606-8522 , Japan.

A cutinase-type polyesterase from Saccharomonospora viridis AHK190 (Cut190) has been shown to degrade the inner block of polyethylene terephthalate. A unique feature of Cut190 is that its function and stability are regulated by Ca binding. Our previous crystal structure analysis of Cut190S226P showed that one Ca binds to the enzyme, which induces large conformational changes in several loop regions to stabilize an open conformation [Miyakawa, T., et al. (2015) Appl. Microbiol. Biotechnol. 99, 4297]. In this study, to analyze the substrate recognition mechanism of Cut190, we determined the crystal structure of the inactive form of a Cut190 mutant, Cut190*S176A, in complex with calcium ions and/or substrates. We found that three calcium ions bind to Cut190*S176A, which is supported by analysis using native mass spectrometry experiments and 3D Reference Interaction Site Model calculations. The complex structures with the two substrates, monoethyl succinate and monoethyl adipate (engaged and open forms), presumably correspond to the pre- and post-reaction states, as the ester bond is close to the active site and pointing outward from the active site, respectively, for the two complexes. Ca binding induces the pocket to open, enabling the substrate to access the pocket more easily. Molecular dynamics simulations suggest that a post-reaction state in the engaged form presumably exists between the experimentally observed forms, indicating that the substrate would be cleaved in the engaged form and then requires the enzyme to change to the open form to release the product, a process that Ca can greatly accelerate.
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http://dx.doi.org/10.1021/acs.biochem.8b00624DOI Listing
September 2018

25 S-Adamantyl-23-yne-26,27-dinor-1α,25-dihydroxyvitamin D: Synthesis, Tissue Selective Biological Activities, and X-ray Crystal Structural Analysis of Its Vitamin D Receptor Complex.

J Med Chem 2018 Aug 23;61(15):6658-6673. Epub 2018 Jul 23.

Department of Biomedical Sciences , Nihon University School of Medicine , Itabashi-ku, Tokyo 173-8610 , Japan.

Both 25 R- and 25 S-25-adamantyl-23-yne-26,27-dinor-1α,25-dihydroxyvitamin D (4a and 4b) were stereoselectively synthesized by a Pd(0)-catalyzed ring closure and Suzuki-Miyaura coupling between enol-triflate 7 and alkenyl-boronic ester 8. The 25 S isomer (4b) showed high vitamin D receptor (VDR) affinity (50% of that of the natural hormone 1α,25-dihydroxyvitamin D, 1) and transactivation potency (kidney HEK293, 90%). In endogenous gene expression, it showed high cell-type selectivity for kidney cells (HEK293, CYP24A1 160% of 1), bone cells (MG63, osteocalcin 64%), and monocytes (U937, CAMP 96%) over intestine (SW480, CYP24A1 8%) and skin (HaCaT, CYP24A1 7%) cells. The X-ray crystal structural analysis of 4b in complex with rat VDR-ligand binding domain (LBD) showed the highest Cα positional shift from the 1/VDR-LBD complex at helix 11. Helix 11 of the 4b and 1 VDR-LBD complexes also showed significant differences in surface properties. These results suggest that 4b should be examined further as another candidate for a mild preventive osteoporosis agent.
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http://dx.doi.org/10.1021/acs.jmedchem.8b00427DOI Listing
August 2018

CD22-Binding Synthetic Sialosides Regulate B Lymphocyte Proliferation Through CD22 Ligand-Dependent and Independent Pathways, and Enhance Antibody Production in Mice.

Front Immunol 2018 19;9:820. Epub 2018 Apr 19.

Department of Immunology, Medical Research Institute, Tokyo Medical and Dental University, Tokyo, Japan.

Sialic acid-binding immunoglobulin-like lectins (Siglecs) are expressed in various immune cells and most of them carry signaling functions. High-affinity synthetic sialoside ligands have been developed for various Siglecs. Therapeutic potentials of the nanoparticles and compounds that contain multiple numbers of these sialosides and other reagents such as toxins and antigens have been demonstrated. However, whether immune responses can be regulated by monomeric sialoside ligands has not yet been known. CD22 (also known as Siglec-2) is an inhibitory molecule preferentially expressed in B lymphocytes (B cells) and is constitutively bound and functionally regulated by α2,6 sialic acids expressed on the same cell (cis-ligands). Here, we developed synthetic sialosides GSC718 and GSC839 that bind to CD22 with high affinity (IC ~100 nM), and inhibit ligand binding of CD22. When B cells are activated by B cell antigen receptor (BCR) ligation, both GSC718 and GSC839 downregulate proliferation of B cells, and this regulation requires both CD22 and α2,6 sialic acids. This result suggests that these sialosides regulate BCR ligation-induced B cell activation by reversing endogenous ligand-mediated regulation of CD22. By contrast, GSC718 and GSC839 augment B cell proliferation induced by TLR ligands or CD40 ligation, and this augmentation requires CD22 but not α2,6 sialic acids. Thus, these sialosides appear to enhance B cell activation by directly suppressing the inhibitory function of CD22 independently of endogenous ligand-mediated regulation. Moreover, GSC839 augments B cell proliferation that depends on both BCR ligation and CD40 ligation as is the case for B cell responses to antigens, and enhanced antibody production to the extent comparable to CpG oligonuleotides or a small amount of alum. Although these known adjuvants induce production of the inflammatory cytokines or accumulation of inflammatory cells, CD22-binding sialosides do not. Thus, synthetic sialosides that bind to CD22 with high-affinity modulate B cell activation through endogenous ligand-dependent and independent pathways, and carry an adjuvant activity without inducing inflammation.
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http://dx.doi.org/10.3389/fimmu.2018.00820DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5917077PMC
June 2019

Crystal Structures and Thermodynamic Analysis Reveal Distinct Mechanisms of CD28 Phosphopeptide Binding to the Src Homology 2 (SH2) Domains of Three Adaptor Proteins.

J Biol Chem 2017 01 6;292(3):1052-1060. Epub 2016 Dec 6.

From the Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, Kyoto 606-8522, Japan,

Full activation of T cells and differentiation into effector T cells are essential for many immune responses and require co-stimulatory signaling via the CD28 receptor. Extracellular ligand binding to CD28 recruits protein-tyrosine kinases to its cytoplasmic tail, which contains a YMNM motif. Following phosphorylation of the tyrosine, the proteins growth factor receptor-bound protein 2 (Grb2), Grb2-related adaptor downstream of Shc (Gads), and p85 subunit of phosphoinositide 3-kinase may bind to pYMNM (where pY is phosphotyrosine) via their Src homology 2 (SH2) domains, leading to downstream signaling to distinct immune pathways. These three adaptor proteins bind to the same site on CD28 with variable affinity, and all are important for CD28-mediated co-stimulatory function. However, the mechanism of how these proteins recognize and compete for CD28 is unclear. To visualize their interactions with CD28, we have determined the crystal structures of Gads SH2 and two p85 SH2 domains in complex with a CD28-derived phosphopeptide. The high resolution structures obtained revealed that, whereas the CD28 phosphopeptide bound to Gads SH2 is in a bent conformation similar to that when bound to Grb2 SH2, it adopts a more extended conformation when bound to the N- and C-terminal SH2 domains of p85. These differences observed in the peptide-protein interactions correlated well with the affinity and other thermodynamic parameters for each interaction determined by isothermal titration calorimetry. The detailed insight into these interactions reported here may inform the development of compounds that specifically inhibit the association of CD28 with these adaptor proteins to suppress excessive T cell responses, such as in allergies and autoimmune diseases.
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http://dx.doi.org/10.1074/jbc.M116.755173DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5247639PMC
January 2017

CD72 negatively regulates B lymphocyte responses to the lupus-related endogenous toll-like receptor 7 ligand Sm/RNP.

J Exp Med 2016 11 24;213(12):2691-2706. Epub 2016 Oct 24.

Department of Immunology, Medical Research Institute, Tokyo Medical and Dental University, Bunkyo, Tokyo 113-8510, Japan

Toll-like receptor 7 (TLR7) plays an essential role in development of systemic lupus erythematosus by co-stimulating B cells reactive to the endogenous TLR7 ligand Sm/ribonucleoprotein (RNP), a crucial lupus self-antigen. However, how the TLR7-mediated autoimmune response is regulated is not yet known. In this study, we demonstrate that CD72, an inhibitory B cell co-receptor known to prevent development of lupus, recognizes Sm/RNP at the extracellular C-type lectin-like domain (CTLD) and specifically inhibits B cell response to Sm/RNP. Moreover, the CTLD of CD72, a lupus-susceptible allele, binds to Sm/RNP less strongly than that of lupus-resistant CD72 Reduced binding of CD72 is supported by x-ray crystallographic analysis that reveals a considerable alteration in charge at the putative ligand-binding site. Thus, CD72 appears to specifically inhibit B cell response to the endogenous TLR7 ligand Sm/RNP through CTLD-mediated recognition of Sm/RNP, thereby preventing production of anti-Sm/RNP antibody crucial for development of lupus.
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http://dx.doi.org/10.1084/jem.20160560DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5110020PMC
November 2016

In-situ and real-time growth observation of high-quality protein crystals under quasi-microgravity on earth.

Sci Rep 2016 Feb 26;6:22127. Epub 2016 Feb 26.

Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.

Precise protein structure determination provides significant information on life science research, although high-quality crystals are not easily obtained. We developed a system for producing high-quality protein crystals with high throughput. Using this system, gravity-controlled crystallization are made possible by a magnetic microgravity environment. In addition, in-situ and real-time observation and time-lapse imaging of crystal growth are feasible for over 200 solution samples independently. In this paper, we also report results of crystallization experiments for two protein samples. Crystals grown in the system exhibited magnetic orientation and showed higher and more homogeneous quality compared with the control crystals. The structural analysis reveals that making use of the magnetic microgravity during the crystallization process helps us to build a well-refined protein structure model, which has no significant structural differences with a control structure. Therefore, the system contributes to improvement in efficiency of structural analysis for "difficult" proteins, such as membrane proteins and supermolecular complexes.
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http://dx.doi.org/10.1038/srep22127DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4768258PMC
February 2016

Modeling and experimental assessment of a buried Leu-Ile mutation in dengue envelope domain III.

Biochem Biophys Res Commun 2016 Feb 28;471(1):163-8. Epub 2016 Jan 28.

Department of Biotechnology and Life Science, Graduate School of Engineering, Tokyo University of Agriculture and Technology, 2-24-16, Nakamachi, Koganei-shi, Tokyo, 184-8588, Japan. Electronic address:

Envelope protein domain III (ED3) of the dengue virus is important for both antibody binding and host cell interaction. Here, we focused on how a L387I mutation in the protein core could take place in DEN4 ED3, but cannot be accommodated in DEN3 ED3 without destabilizing its structure. To this end, we modeled a DEN4_L387I structure using the Penultimate Rotamer Library and taking the DEN4 ED3 main-chain as a fixed template. We found that three out of seven Ile(387) conformers fit in DEN4 ED3 without introducing the severe atomic clashes that are observed when DEN3 serotype's ED3 is used as a template. A more extensive search using 273 side-chain rotamers of the residues surrounding Ile(387) confirmed this prediction. In order to assess the prediction, we determined the crystal structure of DEN4_L387I at 2 Å resolution. Ile(387) indeed adopted one of the three predicted rotamers. Altogether, this study demonstrates that the effects of single mutations are to a large extent successfully predicted by systematically modeling the side-chain structures of the mutated as well as those of its surrounding residues using fixed main-chain structures and assessing inter-atomic steric clashes. More accurate and reliable predictions require considering sub-angstrom main-chain deformation, which remains a challenging task.
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http://dx.doi.org/10.1016/j.bbrc.2016.01.159DOI Listing
February 2016

Structural and biophysical analysis of sero-specific immune responses using epitope grafted Dengue ED3 mutants.

Biochim Biophys Acta 2015 Oct 6;1854(10 Pt A):1438-43. Epub 2015 Jul 6.

Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Tokyo 184-8588, Japan. Electronic address:

Dengue fever is a re-emerging tropical disease and its severe form is caused by cross-reactivity between its four serotypes (DEN1, DEN2, DEN3 and DEN4). The third domain of the viral envelope protein (ED3) contains the two major putative epitopes and is a highly suitable model protein for examining the molecular determinants of a virus' sero-specificity. Here we examine d the sero-specificity and cross-reactivity of the immune response against DEN3 and DEN4 ED3 using six epitope grafted ED3 variants where the surface-exposed epitope residues from DEN3 ED3 were switched to those of DEN4 ED3 and vice versa. We prepared anti-DEN3 and anti-DEN4 ED3 serum by immunizing Swiss albino mice and measured their reactivities against all six grafted mutants. As expected, both sera exhibited strong reactivity against its own serotype's ED3, and little cross-reactivity against their counterpart serotype's ED3s. E2 played a major role in the sero-specificity of anti-DEN3 serum, whereas E1 was important for DEN4 ED3's sero-specificity. Next, the reactivity patterns corroborated our working hypothesis that sero-specificity could be transferred by grafting the surface exposed epitope residues from one serotype to the other. To analyze the above results from a structural viewpoint, we determined the crystal structure of a DEN4 ED3 variant, where E2 was grafted from DEN3 ED3, at 2.78Å resolution and modeled the structures of the five remaining grafted variants by assuming that the overall backbone remained unchanged. The examination of the electrostatic and molecular surfaces of the variants suggested some further rationale for the sero-specificity of the immune responses.
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http://dx.doi.org/10.1016/j.bbapap.2015.07.004DOI Listing
October 2015

The structure of a deoxygenated 400 kDa haemoglobin reveals ternary- and quaternary-structural changes of giant haemoglobins.

Acta Crystallogr D Biol Crystallogr 2014 Jul 29;70(Pt 7):1823-31. Epub 2014 Jun 29.

Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.

The quaternary structures of invertebrate haemoglobins (Hbs) are quite different from those of vertebrate Hbs. The extracellular giant Hbs of molecular masses of about 400 and 3600 kDa are composed of a dome-shaped dodecameric subassembly which consists of four individual globin subunits. Several crystal structures of 400 kDa Hbs from annelids have been reported, including structures in oxygenated and partially unliganded states, but the structure of the fully deoxygenated state has not been reported. In the present study, crystal structures of V2Hb from the tube worm Lamellibrachia satsuma have been determined in both the fully oxygenated and deoxygenated states. A glycosylation site and novel metal-binding sites for divalent cations were clearly observed with no intersubunit interactions in V2Hb. A comparison of the oxygenated and the deoxygenated forms of V2Hb reveals that the ternary- and quaternary-structural changes occur in a manner that maintains the molecular D3 symmetry. These structures suggest that the mechanisms of quaternary-structural changes between the oxy and deoxy states for the giant Hbs are identical across species.
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http://dx.doi.org/10.1107/S1399004714008475DOI Listing
July 2014

Origin of asymmetry at the intersubunit interfaces of V1-ATPase from Thermus thermophilus.

J Mol Biol 2013 Aug 29;425(15):2699-708. Epub 2013 Apr 29.

Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.

V-type ATPase (V-ATPase) is one of the rotary ATPase complexes that mediate energy conversion between the chemical energy of ATP and the ion gradient across the membrane through a rotary catalytic mechanism. Because V-ATPase has structural features similar to those of well-studied F-type ATPase, the structure is expected to highlight the common essence of the torque generation of rotary ATPases. Here, we report a complete model of the extra-membrane domain of the V-ATPase (V1-ATPase) of a thermophilic bacterium, Thermus thermophilus, consisting of three A subunits, three B subunits, one D subunit, and one F subunit. The X-ray structure at 3.9Å resolution provides detailed information about the interactions between A3B3 and DF subcomplexes as well as interactions among the respective subunits, which are defined by the properties of side chains. Asymmetry at the intersubunit interfaces was detected from the structural differences among the three AB pairs in the different reaction states, while the large interdomain motion in the catalytic A subunits was not observed unlike F1 from various species and V1 from Enterococcus hirae. Asymmetry is mainly realized by rigid-body rearrangements of the relative position between A and B subunits. This is consistent with the previous observations by the high-resolution electron microscopy for the whole V-ATPase complexes. Therefore, our result plausibly implies that the essential motion for the torque generation is not the large interdomain movement of the catalytic subunits but the rigid-body rearrangement of subunits.
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http://dx.doi.org/10.1016/j.jmb.2013.04.022DOI Listing
August 2013

A P39R mutation at the N-terminal domain of human αB-crystallin regulates its oligomeric state and chaperone-like activity.

Biochem Biophys Res Commun 2012 Aug 1;425(3):601-6. Epub 2012 Aug 1.

Research Reactor Institute, Kyoto University, Kumatori, Sennan, Osaka 590-0494, Japan.

Recent structure analyses of αB-crystallin have proposed some models of the N-terminal domain and the manner of oligomerization, whereas the effects of the significantly high content of Pro residues at the N-terminal domain remain unclear. We report the properties of a novel P39R mutant of αB-crystallin. The content of α-helix was increased, and the molecular size of the P39R mutant was larger than that of wild-type αB-crystallin. A slight loss of chaperone-like activity was observed using alcohol dehydrogenase (ADH), while a significant increase was detected by insulin assay. The Pro residue at the N-terminal domain of αB-crystallin is important for oligomerization and function.
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http://dx.doi.org/10.1016/j.bbrc.2012.07.138DOI Listing
August 2012

Inter-subunit interaction and quaternary rearrangement defined by the central stalk of prokaryotic V1-ATPase.

EMBO Rep 2009 Nov 25;10(11):1228-34. Epub 2009 Sep 25.

Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.

V-type ATPases (V-ATPases) are categorized as rotary ATP synthase/ATPase complexes. The V-ATPases are distinct from F-ATPases in terms of their rotation scheme, architecture and subunit composition. However, there is no detailed structural information on V-ATPases despite the abundant biochemical and biophysical research. Here, we report a crystallographic study of V1-ATPase, from Thermus thermophilus, which is a soluble component consisting of A, B, D and F subunits. The structure at 4.5 A resolution reveals inter-subunit interactions and nucleotide binding. In particular, the structure of the central stalk composed of D and F subunits was shown to be characteristic of V1-ATPases. Small conformational changes of respective subunits and significant rearrangement of the quaternary structure observed in the three AB pairs were related to the interaction with the straight central stalk. The rotation mechanism is discussed based on a structural comparison between V1-ATPases and F1-ATPases.
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http://dx.doi.org/10.1038/embor.2009.202DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2775172PMC
November 2009

Structural basis for the heterotropic and homotropic interactions of invertebrate giant hemoglobin.

Biochemistry 2008 Oct 4;47(43):11231-8. Epub 2008 Oct 4.

Department of Chemistry, Graduate School of Science, Kyoto UniVersity, Sakyo-ku, Kyoto 606-8502, Japan.

The oxygen binding properties of extracellular giant hemoglobins (Hbs) in some annelids exhibit features significantly different from those of vertebrate tetrameric Hbs. Annelid giant Hbs show cooperative oxygen binding properties in the presence of inorganic cations, while the cooperativities of vertebrate Hbs are enhanced by small organic anions or chloride ions. To elucidate the structural basis for the cation-mediated cooperative mechanisms of these giant Hbs, we determined the crystal structures of Ca2+- and Mg2+-bound Hbs from Oligobrachia mashikoi at 1.6 and 1.7 A resolution, respectively. Both of the metal-bound structures were determined in the oxygenated state. Four Ca2+-binding sites and one Mg2+-binding site were identified in each tetramer subassembly. These cations are considered to stabilize the oxygenated form and increase affinity and cooperativity for oxygen binding, as almost all of the Ca2+ and Mg2+ cations were bound at the interface regions, forming either direct or hydrogen bond-mediated interactions with the neighboring subunits. A comparison of the structures of the oxygenated form and the partially unliganded form provides structural insight into proton-coupled cooperativity (Bohr effect) and ligand-induced transitions. Two histidine residues are assumed to be primarily associated with the Bohr effect. With regard to the ligand-induced cooperativity, a novel quaternary rotation mechanism is proposed to exist at the interface region of the dimer subassembly. Interactions among conserved residues Arg E10, His F3, Gln F7, and Val E11, together with the bending motion of the heme molecules, appear to be essential for quaternary rearrangement.
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http://dx.doi.org/10.1021/bi8012609DOI Listing
October 2008

Structure of the partially unliganded met state of 400 kDa hemoglobin: insights into ligand-induced structural changes of giant hemoglobins.

Proteins 2008 Oct;73(1):113-25

Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-Ku, Kyoto 606-8502, Japan.

Recent crystallographic studies have revealed the structures of some invertebrate extracellular giant hemoglobins of 3,600 kDa or 400 kDa and their common quaternary structure of dodecameric subassembly composed of four kinds of globin subunits (A1, A2, B1, and B2). These results have provided insight into the mechanisms of their unique functional properties of oxygen binding and sulfide binding. All of these structures were solved with oxygenated or CO-liganded forms at low or moderate resolutions. We have determined the crystal structure of 400 kDa Hb from a polychaete Oligobrachia mashikoi at 1.95 A resolution. The electron densities at higher resolution confirm the existence of an isoform of the B1 subunit because of the inconsistency with the model that was built from the formerly known amino acid sequence. The brownish color of the crystals used in this study and the absorption spectrum from the dissolved crystals strongly indicated that the obtained structure was a ferric met state, whereas complete absence of electron density around the distal heme pockets were observed at the A2, B1, and B2 subunits. We concluded that the obtained structure was in unliganded met forms at three of four globin subunits in the 24mer assembly and in oxygenated forms at the remaining A1 subunits. The partially unliganded structure showed remarkable structural changes at the AB loop regions causing quaternary rearrangements of the EF-dimer structure. In contrast, few changes occurred at the interface regions composed of the E and F helices. These results suggest that the ligand-induced structural changes of Oligobrachia Hb are quite different from those of the well-studied mollusk Hb having the same EF-dimer structure. The structural rearrangements make the dodecameric subassembly form a tighter conformation than those of fully oxygenated or CO-liganded dodecamer structure.
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http://dx.doi.org/10.1002/prot.22040DOI Listing
October 2008

Crystal structure of archaeal photolyase from Sulfolobus tokodaii with two FAD molecules: implication of a novel light-harvesting cofactor.

J Mol Biol 2007 Jan 7;365(4):903-10. Epub 2006 Oct 7.

Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.

UV exposure of DNA molecules induces serious DNA lesions. The cyclobutane pyrimidine dimer (CPD) photolyase repairs CPD-type - lesions by using the energy of visible light. Two chromophores for different roles have been found in this enzyme family; one catalyzes the CPD repair reaction and the other works as an antenna pigment that harvests photon energy. The catalytic cofactor of all known photolyases is FAD, whereas several light-harvesting cofactors are found. Currently, 5,10-methenyltetrahydrofolate (MTHF), 8-hydroxy-5-deaza-riboflavin (8-HDF) and FMN are the known light-harvesting cofactors, and some photolyases lack the chromophore. Three crystal structures of photolyases from Escherichia coli (Ec-photolyase), Anacystis nidulans (An-photolyase), and Thermus thermophilus (Tt-photolyase) have been determined; however, no archaeal photolyase structure is available. A similarity search of archaeal genomic data indicated the presence of a homologous gene, ST0889, on Sulfolobus tokodaii strain7. An enzymatic assay reveals that ST0889 encodes photolyase from S. tokodaii (St-photolyase). We have determined the crystal structure of the St-photolyase protein to confirm its structural features and to investigate the mechanism of the archaeal DNA repair system with light energy. The crystal structure of the St-photolyase is superimposed very well on the three known photolyases including the catalytic cofactor FAD. Surprisingly, another FAD molecule is found at the position of the light-harvesting cofactor. This second FAD molecule is well accommodated in the crystal structure, suggesting that FAD works as a novel light-harvesting cofactor of photolyase. In addition, two of the four CPD recognition residues in the crystal structure of An-photolyase are not found in St-photolyase, which might utilize a different mechanism to recognize the CPD from that of An-photolyase.
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http://dx.doi.org/10.1016/j.jmb.2006.10.012DOI Listing
January 2007

Structure of an extracellular giant hemoglobin of the gutless beard worm Oligobrachia mashikoi.

Proc Natl Acad Sci U S A 2005 Oct 3;102(41):14521-6. Epub 2005 Oct 3.

Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.

Mouthless and gutless marine animals, pogonophorans and vestimentiferans, obtain their nutrition solely from their symbiotic chemoautotrophic sulfur-oxidizing bacteria. These animals have sulfide-binding 400-kDa and/or 3,500-kDa Hb, which transports oxygen and sulfide simultaneously. The symbiotic bacteria are supplied with sulfide by Hb of the host animal and use it to provide carbon compounds. Here, we report the crystal structure of a 400-kDa Hb from pogonophoran Oligobrachia mashikoi at 2.85-A resolution. The structure is hollow-spherical, composed of a total of 24 globins as a dimer of dodecamer. This dodecameric assemblage would be a fundamental structural unit of both 400-kDa and 3,500-kDa Hbs. The structure of the mercury derivative used for phasing provides insights into the sulfide-binding mechanism. The mercury compounds bound to all free Cys residues that have been expected as sulfide-binding sites. Some of the free Cys residues are surrounded by Phe aromatic rings, and mercury atoms come into contact with these residues in the derivative structure. It is strongly suggested that sulfur atoms bound to these sites could be stabilized by aromatic-electrostatic interactions by the surrounding Phe residues.
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http://dx.doi.org/10.1073/pnas.0501541102DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1253539PMC
October 2005

Crystallization and preliminary X-ray crystallographic analysis of extracellular giant hemoglobin from pogonophoran Oligobrachia mashikoi.

Biochim Biophys Acta 2005 Jun;1750(2):173-6

Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan; RIKEN Harima Institute/SPring-8, Koto 1-1-1, Mikazuki-cho, Sayo-gun, Hyogo 679-5148, Japan.

An extracellular giant hemoglobin of Oligobrachia mashikoi, composed of 24 globins with the molecular mass of approximately 400 kDa was crystallized in its intact form. Two crystal forms were obtained by the vapor-diffusion method. Form I crystals obtained using sodium acetate as a precipitant belong to the space group P6(1)22 or P6(5)22, with unit-cell parameters a=112.41, c=621.25 A, and diffracted X-rays beyond 3.0 A resolution. Form II crystals obtained using PEG 10000 as a precipitant belong to the space group R32, with unit-cell parameters a=111.50, c=276.84 A, and diffracted X-rays beyond 2.9 A resolution. The crystals are suitable for X-ray crystallography to determine the supramacromolecular assembly of this giant hemoglobin.
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http://dx.doi.org/10.1016/j.bbapap.2005.05.009DOI Listing
June 2005

Crystal structure of the Co-chaperonin Cpn10 from Thermus thermophilus HB8.

Proteins 2005 Feb;58(2):498-500

Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.

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http://dx.doi.org/10.1002/prot.20317DOI Listing
February 2005

Structure of the C subunit of V-type ATPase from Thermus thermophilus at 1.85 A resolution.

Acta Crystallogr D Biol Crystallogr 2004 May 21;60(Pt 5):810-5. Epub 2004 Apr 21.

Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.

The V-type H(+)-ATPases are similar to the F-type ATP synthases in their structure and functional mechanism. They hydrolyze ATP coupled with proton translocation across a membrane, but in some archaea and eubacteria they also synthesize ATP in the reverse reaction. The C subunit is one of the components of the membrane-bound V(0) moiety of V-type ATPases. The C subunit of V-type H(+)-ATPase from Thermus thermophilus was crystallized in a monoclinic form and its crystal structure was determined at 1.85 A resolution by the MAD method using selenomethionyl protein. The structure has a cone (tapered cylinder) shape consisting of only two types of helix (long and short) as secondary-structure elements. The molecule is divided into three similar domains, each of which has essentially the same topology. On the basis of the structural features and molecular-surface charge distribution, it is suggested that the bottom side of the C subunit is a possible binding site for the V(0) proteolipid L-subunit ring and that the C subunit might function as a spacer unit between the proteolipid L-subunit ring and the rotating V(1) central shaft.
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http://dx.doi.org/10.1107/S0907444904003257DOI Listing
May 2004