1
|
Tumba NL, Naicker P, Stoychev S, Killick MA, Owen GR, Papathanasopoulos MA. Covalent binding of human two-domain CD4 to an HIV-1 subtype C SOSIP.664 trimer modulates its structural dynamics. Biochem Biophys Res Commun 2022; 612:181-187. [PMID: 35550505 DOI: 10.1016/j.bbrc.2022.04.101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2022] [Accepted: 04/21/2022] [Indexed: 11/02/2022]
Abstract
The human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (Env) mediates host cell infection by binding to the cellular receptor CD4. Recombinant Env bound to CD4 has been explored for its potential as an HIV vaccine immunogen as receptor binding exposes otherwise shielded, conserved functional sites. Previous preclinical studies showed an interchain disulphide linkage facilitated between Env and 2dCD4S60C generates an immunogenic complex that elicits potent, broadly neutralizing antibodies (bNAbs) against clinically relevant HIV-1. This study investigated conformational dynamics of 2dCD4WT and 2dCD4S60C bound to an HIV-1C SOSIP.664 Env trimer using hydrogen-deuterium exchange mass spectrometry. The Env:2dCD4S60C complex maintains key contact residues required for MHCII and Env/gp120 binding and the residues encompassing Ibalizumab's epitope. Important residues remaining anchored, with an increased flexibility in surrounding regions, evidenced by the higher exchange seen in flanking residues compared to Env:2dCD4WT. While changes in Env:2dCD4S60C dynamics in domain 1 were moderate, domain 2 exhibited greater variation. Lack of stability-inducing H-bonds in these allosteric sites suggest the improved immunogenicity of Env:2dCD4S60C result from exposed CD4 residues providing diverse/novel antigenic targets for the development of potent, broadly neutralizing Ibalizumab-like antibodies.
Collapse
Affiliation(s)
- Nancy L Tumba
- HIV Pathogenesis Research Unit, Department of Molecular Medicine and Haematology, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown, 2193, Johannesburg, South Africa
| | - Previn Naicker
- Council for Scientific and Industrial Research, Biosciences, Pretoria, 0001, South Africa
| | - Stoyan Stoychev
- Council for Scientific and Industrial Research, Biosciences, Pretoria, 0001, South Africa
| | - Mark A Killick
- HIV Pathogenesis Research Unit, Department of Molecular Medicine and Haematology, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown, 2193, Johannesburg, South Africa
| | - Gavin R Owen
- HIV Pathogenesis Research Unit, Department of Molecular Medicine and Haematology, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown, 2193, Johannesburg, South Africa.
| | - Maria A Papathanasopoulos
- HIV Pathogenesis Research Unit, Department of Molecular Medicine and Haematology, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown, 2193, Johannesburg, South Africa
| |
Collapse
|
2
|
Meirson T, Bomze D, Markel G. Structural basis of SARS-CoV-2 spike protein induced by ACE2. Bioinformatics 2021; 37:929-936. [PMID: 32818261 PMCID: PMC7558967 DOI: 10.1093/bioinformatics/btaa744] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2020] [Revised: 07/20/2020] [Accepted: 08/14/2020] [Indexed: 12/24/2022] Open
Abstract
Motivation The recent emergence of the novel SARS-coronavirus 2 (SARS-CoV-2) and its international
spread pose a global health emergency. The spike (S) glycoprotein binds ACE2 and
promotes SARS-CoV-2 entry into host cells. The trimeric S protein binds the receptor
using the receptor-binding domain (RBD) causing conformational changes in S protein that
allow priming by host cell proteases. Unraveling the dynamic structural features used by
SARS-CoV-2 for entry might provide insights into viral transmission and reveal novel
therapeutic targets. Using structures determined by X-ray crystallography and cryo-EM,
we performed structural analysis and atomic comparisons of the different conformational
states adopted by the SARS-CoV-2-RBD. Results Here, we determined the key structural components induced by the receptor and
characterized their intramolecular interactions. We show that κ-helix (polyproline-II)
is a predominant structure in the binding interface and in facilitating the conversion
to the active form of the S protein. We demonstrate a series of conversions between
switch-like κ-helix and β-strand, and conformational variations in a set of short
α-helices which affect the hinge region. These conformational changes lead to an
alternating pattern in conserved disulfide bond configurations positioned at the hinge,
indicating a possible disulfide exchange, an important allosteric switch implicated in
viral entry of various viruses, including HIV and murine coronavirus. The structural
information presented herein enables to inspect and understand the important dynamic
features of SARS-CoV-2-RBD and propose a novel potential therapeutic strategy to block
viral entry. Overall, this study provides guidance for the design and optimization of
structure-based intervention strategies that target SARS-CoV-2. Availability We have implemented the proposed methods in an R package freely available at https://github.com/Grantlab/bio3d Supplementary information Supplementary data are
available at Bioinformatics online.
Collapse
Affiliation(s)
- Tomer Meirson
- Ella Lemelbaum Institute for Immuno-oncology, Sheba Medical Center, Ramat-Gan 526260, Israel.,The Azrieli Faculty of Medicine, Bar-Ilan University, Safed 1311502, Israel
| | | | - Gal Markel
- Ella Lemelbaum Institute for Immuno-oncology, Sheba Medical Center, Ramat-Gan 526260, Israel.,Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 6997801, Israel.,Department of Clinical Microbiology and Immunology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 6997801, Israel
| |
Collapse
|
3
|
Mørch AM, Bálint Š, Santos AM, Davis SJ, Dustin ML. Coreceptors and TCR Signaling - the Strong and the Weak of It. Front Cell Dev Biol 2020; 8:597627. [PMID: 33178706 PMCID: PMC7596257 DOI: 10.3389/fcell.2020.597627] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2020] [Accepted: 09/28/2020] [Indexed: 12/02/2022] Open
Abstract
The T-cell coreceptors CD4 and CD8 have well-characterized and essential roles in thymic development, but how they contribute to immune responses in the periphery is unclear. Coreceptors strengthen T-cell responses by many orders of magnitude - beyond a million-fold according to some estimates - but the mechanisms underlying these effects are still debated. T-cell receptor (TCR) triggering is initiated by the binding of the TCR to peptide-loaded major histocompatibility complex (pMHC) molecules on the surfaces of other cells. CD4 and CD8 are the only T-cell proteins that bind to the same pMHC ligand as the TCR, and can directly associate with the TCR-phosphorylating kinase Lck. At least three mechanisms have been proposed to explain how coreceptors so profoundly amplify TCR signaling: (1) the Lck recruitment model and (2) the pseudodimer model, both invoked to explain receptor triggering per se, and (3) two-step coreceptor recruitment to partially triggered TCRs leading to signal amplification. More recently it has been suggested that, in addition to initiating or augmenting TCR signaling, coreceptors effect antigen discrimination. But how can any of this be reconciled with TCR signaling occurring in the absence of CD4 or CD8, and with their interactions with pMHC being among the weakest specific protein-protein interactions ever described? Here, we review each theory of coreceptor function in light of the latest structural, biochemical, and functional data. We conclude that the oldest ideas are probably still the best, i.e., that their weak binding to MHC proteins and efficient association with Lck allow coreceptors to amplify weak incipient triggering of the TCR, without comprising TCR specificity.
Collapse
Affiliation(s)
- Alexander M. Mørch
- The Kennedy Institute of Rheumatology, University of Oxford, Oxford, United Kingdom
- Radcliffe Department of Medicine, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom
- MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, United Kingdom
| | - Štefan Bálint
- The Kennedy Institute of Rheumatology, University of Oxford, Oxford, United Kingdom
| | - Ana Mafalda Santos
- Radcliffe Department of Medicine, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom
- MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, United Kingdom
| | - Simon J. Davis
- Radcliffe Department of Medicine, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom
- MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, United Kingdom
| | - Michael L. Dustin
- The Kennedy Institute of Rheumatology, University of Oxford, Oxford, United Kingdom
| |
Collapse
|
4
|
Llorente García I, Marsh M. A biophysical perspective on receptor-mediated virus entry with a focus on HIV. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2020; 1862:183158. [PMID: 31863725 PMCID: PMC7156917 DOI: 10.1016/j.bbamem.2019.183158] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/27/2019] [Revised: 12/12/2019] [Accepted: 12/13/2019] [Indexed: 12/14/2022]
Abstract
As part of their entry and infection strategy, viruses interact with specific receptor molecules expressed on the surface of target cells. The efficiency and kinetics of the virus-receptor interactions required for a virus to productively infect a cell is determined by the biophysical properties of the receptors, which are in turn influenced by the receptors' plasma membrane (PM) environments. Currently, little is known about the biophysical properties of these receptor molecules or their engagement during virus binding and entry. Here we review virus-receptor interactions focusing on the human immunodeficiency virus type 1 (HIV), the etiological agent of acquired immunodeficiency syndrome (AIDS), as a model system. HIV is one of the best characterised enveloped viruses, with the identity, roles and structure of the key molecules required for infection well established. We review current knowledge of receptor-mediated HIV entry, addressing the properties of the HIV cell-surface receptors, the techniques used to measure these properties, and the macromolecular interactions and events required for virus entry. We discuss some of the key biophysical principles underlying receptor-mediated virus entry and attempt to interpret the available data in the context of biophysical mechanisms. We also highlight crucial outstanding questions and consider how new tools might be applied to advance understanding of the biophysical properties of viral receptors and the dynamic events leading to virus entry.
Collapse
Affiliation(s)
| | - Mark Marsh
- Medical Research Council Laboratory for Molecular Cell Biology, University College London, London, UK
| |
Collapse
|
5
|
Donnelly DP, Dowgiallo MG, Salisbury JP, Aluri KC, Iyengar S, Chaudhari M, Mathew M, Miele I, Auclair JR, Lopez SA, Manetsch R, Agar JN. Cyclic Thiosulfinates and Cyclic Disulfides Selectively Cross-Link Thiols While Avoiding Modification of Lone Thiols. J Am Chem Soc 2018; 140:7377-7380. [PMID: 29851341 DOI: 10.1021/jacs.8b01136] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
This work addresses the need for chemical tools that can selectively form cross-links. Contemporary thiol-selective cross-linkers, for example, modify all accessible thiols, but only form cross-links between a subset. The resulting terminal "dead-end" modifications of lone thiols are toxic, confound cross-linking-based studies of macromolecular structure, and are an undesired, and currently unavoidable, byproduct in polymer synthesis. Using the thiol pair of Cu/Zn-superoxide dismutase (SOD1), we demonstrated that cyclic disulfides, including the drug/nutritional supplement lipoic acid, efficiently cross-linked thiol pairs but avoided dead-end modifications. Thiolate-directed nucleophilic attack upon the cyclic disulfide resulted in thiol-disulfide exchange and ring cleavage. The resulting disulfide-tethered terminal thiolate moiety either directed the reverse reaction, releasing the cyclic disulfide, or participated in oxidative disulfide (cross-link) formation. We hypothesized, and confirmed with density functional theory (DFT) calculations, that mono- S-oxo derivatives of cyclic disulfides formed a terminal sulfenic acid upon ring cleavage that obviated the previously rate-limiting step, thiol oxidation, and accelerated the new rate-determining step, ring cleavage. Our calculations suggest that the origin of accelerated ring cleavage is improved frontier molecular orbital overlap in the thiolate-disulfide interchange transition. Five- to seven-membered cyclic thiosulfinates were synthesized and efficiently cross-linked up to 104-fold faster than their cyclic disulfide precursors; functioned in the presence of biological concentrations of glutathione; and acted as cell-permeable, potent, tolerable, intracellular cross-linkers. This new class of thiol cross-linkers exhibited click-like attributes including, high yields driven by the enthalpies of disulfide and water formation, orthogonality with common functional groups, water-compatibility, and ring strain-dependence.
Collapse
Affiliation(s)
- Daniel P Donnelly
- Department of Chemistry and Chemical Biology , Northeastern University , 360 Huntington Avenue , Boston , Massachusetts 02115 , United States.,Barnett Institute of Chemical and Biological Analysis , Northeastern University , 360 Huntington Avenue , Boston , Massachusetts 02115 , United States
| | - Matthew G Dowgiallo
- Department of Chemistry and Chemical Biology , Northeastern University , 360 Huntington Avenue , Boston , Massachusetts 02115 , United States
| | - Joseph P Salisbury
- Department of Chemistry and Chemical Biology , Northeastern University , 360 Huntington Avenue , Boston , Massachusetts 02115 , United States.,Barnett Institute of Chemical and Biological Analysis , Northeastern University , 360 Huntington Avenue , Boston , Massachusetts 02115 , United States
| | - Krishna C Aluri
- Department of Chemistry and Chemical Biology , Northeastern University , 360 Huntington Avenue , Boston , Massachusetts 02115 , United States.,Barnett Institute of Chemical and Biological Analysis , Northeastern University , 360 Huntington Avenue , Boston , Massachusetts 02115 , United States
| | - Suhasini Iyengar
- Department of Chemistry and Chemical Biology , Northeastern University , 360 Huntington Avenue , Boston , Massachusetts 02115 , United States
| | - Meenal Chaudhari
- Department of Chemistry and Chemical Biology , Northeastern University , 360 Huntington Avenue , Boston , Massachusetts 02115 , United States.,Barnett Institute of Chemical and Biological Analysis , Northeastern University , 360 Huntington Avenue , Boston , Massachusetts 02115 , United States
| | - Merlit Mathew
- Department of Chemistry and Chemical Biology , Northeastern University , 360 Huntington Avenue , Boston , Massachusetts 02115 , United States
| | - Isabella Miele
- Department of Chemistry and Chemical Biology , Northeastern University , 360 Huntington Avenue , Boston , Massachusetts 02115 , United States
| | - Jared R Auclair
- Department of Chemistry and Chemical Biology , Northeastern University , 360 Huntington Avenue , Boston , Massachusetts 02115 , United States.,Barnett Institute of Chemical and Biological Analysis , Northeastern University , 360 Huntington Avenue , Boston , Massachusetts 02115 , United States
| | - Steven A Lopez
- Department of Chemistry and Chemical Biology , Northeastern University , 360 Huntington Avenue , Boston , Massachusetts 02115 , United States
| | - Roman Manetsch
- Department of Chemistry and Chemical Biology , Northeastern University , 360 Huntington Avenue , Boston , Massachusetts 02115 , United States.,Department of Pharmaceutical Sciences , Northeastern University , 360 Huntington Avenue , Boston , Massachusetts 02115 , United States
| | - Jeffrey N Agar
- Department of Chemistry and Chemical Biology , Northeastern University , 360 Huntington Avenue , Boston , Massachusetts 02115 , United States.,Barnett Institute of Chemical and Biological Analysis , Northeastern University , 360 Huntington Avenue , Boston , Massachusetts 02115 , United States.,Department of Pharmaceutical Sciences , Northeastern University , 360 Huntington Avenue , Boston , Massachusetts 02115 , United States
| |
Collapse
|
6
|
Owen GR, Le D, Stoychev S, Cerutti NM, Papathanasopoulos M. Redox exchange of the disulfides of human two-domain CD4 regulates the conformational dynamics of each domain, providing insight into its mechanisms of control. Biochem Biophys Res Commun 2018; 497:811-817. [PMID: 29470989 DOI: 10.1016/j.bbrc.2018.02.161] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2018] [Accepted: 02/18/2018] [Indexed: 11/18/2022]
Abstract
CD4, a membrane glycoprotein expressed by specific leukocytes, plays a vital role in the human immune response and acts as a primary receptor for HIV entry. Of its four ecto-domains (D1-D4), D1, D2, and D4 each contain a distinctive disulfide bond. Whereas the disulfides of D1 and D4 are more traditional in nature, providing structural functions, that of D2 is referred to as an "allosteric" disulfide due to its high dihedral strain energy and relative ease of reduction that is thought to regulate CD4 structure and function by shuffling its redox state. While we have shown previously that elimination of the pre-stressed D2 disulfide results in a favorable structural collapse that increases the stability of a CD4 variant comprising only D1 and D2 (2dCD4), we sought to further localize and determine the nature of the biophysical modifications that take place upon redox exchange of the D1 and D2 disulfides by using amide hydrogen-deuterium exchange mass spectrometry (HDX-MS) to measure induced changes in conformational dynamics. By analyzing various redox isomers of 2dCD4, we demonstrate that ablation of the D1 disulfide enhances the dynamics of the domain considerably, with little effect on that of D2. Reduction of the D2 disulfide however decreases the conformational dynamics of many of the β-strands of the domain that enclose the bond, suggesting a model in which inward collapse of secondary structure occurs around the allosteric disulfide upon its eradication, resulting in a marked decrease in hydrodynamic volume and increase in stability as previously described. Increases in the dynamics of regions important for HIV gp120 and MHCII binding in D1 also result allosterically after reducing the D2 disulfide, which are likely a consequence of the structural changes that take place in D2, findings that advance our understanding of the mechanisms by which redox exchange of the CD4 disulfides regulates its function.
Collapse
Affiliation(s)
- Gavin R Owen
- HIV Pathogenesis Research Unit, Department of Molecular Medicine and Haematology, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown, 2193, Johannesburg, South Africa.
| | - Doris Le
- HIV Pathogenesis Research Unit, Department of Molecular Medicine and Haematology, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown, 2193, Johannesburg, South Africa
| | - Stoyan Stoychev
- Council for Scientific and Industrial Research, Biosciences, Pretoria, 0001, South Africa
| | - Nichole M Cerutti
- HIV Pathogenesis Research Unit, Department of Molecular Medicine and Haematology, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown, 2193, Johannesburg, South Africa
| | - Maria Papathanasopoulos
- HIV Pathogenesis Research Unit, Department of Molecular Medicine and Haematology, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown, 2193, Johannesburg, South Africa
| |
Collapse
|
7
|
Bechtel TJ, Weerapana E. From structure to redox: The diverse functional roles of disulfides and implications in disease. Proteomics 2017; 17. [PMID: 28044432 DOI: 10.1002/pmic.201600391] [Citation(s) in RCA: 92] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2016] [Revised: 12/02/2016] [Accepted: 12/28/2016] [Indexed: 12/16/2022]
Abstract
This review provides a comprehensive overview of the functional roles of disulfide bonds and their relevance to human disease. The critical roles of disulfide bonds in protein structure stabilization and redox regulation of protein activity are addressed. Disulfide bonds are essential to the structural stability of many proteins within the secretory pathway and can exist as intramolecular or inter-domain disulfides. The proper formation of these bonds often relies on folding chaperones and oxidases such as members of the protein disulfide isomerase (PDI) family. Many of the PDI family members catalyze disulfide-bond formation, reduction, and isomerization through redox-active disulfides and perturbed PDI activity is characteristic of carcinomas and neurodegenerative diseases. In addition to catalytic function in oxidoreductases, redox-active disulfides are also found on a diverse array of cellular proteins and act to regulate protein activity and localization in response to oxidative changes in the local environment. These redox-active disulfides are either dynamic intramolecular protein disulfides or mixed disulfides with small-molecule thiols generating glutathionylation and cysteinylation adducts. The oxidation and reduction of redox-active disulfides are mediated by cellular reactive oxygen species and activity of reductases, such as glutaredoxin and thioredoxin. Dysregulation of cellular redox conditions and resulting changes in mixed disulfide formation are directly linked to diseases such as cardiovascular disease and Parkinson's disease.
Collapse
Affiliation(s)
- Tyler J Bechtel
- Department of Chemistry, Boston College, Chestnut Hill, MA, USA
| | | |
Collapse
|
8
|
Structural basis for ligand binding to an enzyme by a conformational selection pathway. Proc Natl Acad Sci U S A 2017; 114:6298-6303. [PMID: 28559350 DOI: 10.1073/pnas.1700919114] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Proteins can bind target molecules through either induced fit or conformational selection pathways. In the conformational selection model, a protein samples a scarcely populated high-energy state that resembles a target-bound conformation. In enzymatic catalysis, such high-energy states have been identified as crucial entities for activity and the dynamic interconversion between ground states and high-energy states can constitute the rate-limiting step for catalytic turnover. The transient nature of these states has precluded direct observation of their properties. Here, we present a molecular description of a high-energy enzyme state in a conformational selection pathway by an experimental strategy centered on NMR spectroscopy, protein engineering, and X-ray crystallography. Through the introduction of a disulfide bond, we succeeded in arresting the enzyme adenylate kinase in a closed high-energy conformation that is on-pathway for catalysis. A 1.9-Å X-ray structure of the arrested enzyme in complex with a transition state analog shows that catalytic sidechains are properly aligned for catalysis. We discovered that the structural sampling of the substrate free enzyme corresponds to the complete amplitude that is associated with formation of the closed and catalytically active state. In addition, we found that the trapped high-energy state displayed improved ligand binding affinity, compared with the wild-type enzyme, demonstrating that substrate binding to the high-energy state is not occluded by steric hindrance. Finally, we show that quenching of fast time scale motions observed upon ligand binding to adenylate kinase is dominated by enzyme-substrate interactions and not by intramolecular interactions resulting from the conformational change.
Collapse
|
9
|
Plugis NM, Palanski BA, Weng CH, Albertelli M, Khosla C. Thioredoxin-1 Selectively Activates Transglutaminase 2 in the Extracellular Matrix of the Small Intestine: IMPLICATIONS FOR CELIAC DISEASE. J Biol Chem 2016; 292:2000-2008. [PMID: 28003361 DOI: 10.1074/jbc.m116.767988] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Revised: 12/13/2016] [Indexed: 11/06/2022] Open
Abstract
Transglutaminase 2 (TG2) catalyzes transamidation or deamidation of its substrates and is ordinarily maintained in a catalytically inactive state in the intestine and other organs. Aberrant TG2 activity is thought to play a role in celiac disease, suggesting that a better understanding of TG2 regulation could help to elucidate the mechanistic basis of this malady. Structural and biochemical analysis has led to the hypothesis that extracellular TG2 activation involves reduction of an allosteric disulfide bond by thioredoxin-1 (TRX), but cellular and in vivo evidence for this proposal is lacking. To test the physiological relevance of this hypothesis, we first showed that macrophages exposed to pro-inflammatory stimuli released TRX in sufficient quantities to activate their extracellular pools of TG2. By using the C35S mutant of TRX, which formed a metastable mixed disulfide bond with TG2, we demonstrated that these proteins specifically recognized each other in the extracellular matrix of fibroblasts. When injected into mice and visualized with antibodies, we observed the C35S TRX mutant bound to endogenous TG2 as its principal protein partner in the small intestine. Control experiments showed no labeling of TG2 knock-out mice. Intravenous administration of recombinant TRX in wild-type mice, but not TG2 knock-out mice, led to a rapid rise in intestinal transglutaminase activity in a manner that could be inhibited by small molecules targeting TG2 or TRX. Our findings support the potential pathophysiological relevance of TRX in celiac disease and establish the Cys370-Cys371 disulfide bond of TG2 as one of clearest examples of an allosteric disulfide bond in mammals.
Collapse
Affiliation(s)
- Nicholas M Plugis
- From the Department of Chemistry, Stanford University, Stanford, California 94305
| | - Brad A Palanski
- From the Department of Chemistry, Stanford University, Stanford, California 94305
| | - Chih-Hisang Weng
- From the Department of Chemistry, Stanford University, Stanford, California 94305; the School of Medicine, Stanford University, Stanford, California 94305; the Medical Science Training Program, Stanford University, Stanford, California 94305
| | - Megan Albertelli
- Department of Comparative Medicine, Stanford University, Stanford, California 94305
| | - Chaitan Khosla
- From the Department of Chemistry, Stanford University, Stanford, California 94305; Department of Chemical Engineering, Stanford University, Stanford, California 94305; Stanford ChEM-H, Stanford University, Stanford, California 94305.
| |
Collapse
|
10
|
Moolla N, Killick M, Papathanasopoulos M, Capovilla A. Thioredoxin (Trx1) regulates CD4 membrane domain localization and is required for efficient CD4-dependent HIV-1 entry. Biochim Biophys Acta Gen Subj 2016; 1860:1854-63. [PMID: 27233453 DOI: 10.1016/j.bbagen.2016.05.030] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2016] [Revised: 05/12/2016] [Accepted: 05/21/2016] [Indexed: 11/25/2022]
Abstract
BACKGROUND CD4 is a glycoprotein expressed on the surfaces of certain immune cells. On lymphocytes, an important function of CD4 is to co-engage Major Histocompatibility Complex (MHC) molecules with the T Cell Receptor (TCR), a process that is essential for antigen-specific activation of T cells. CD4 localizes dynamically into distinct membrane microdomains, an important feature of its immunoregulatory function that has also been shown to influence the efficiency of HIV replication. However, the mechanism by which CD4 localization is regulated and the biological significance of this is incompletely understood. METHODS In this study, we used confocal microscopy, density-gradient centrifugation and flow cytometry to analyze dynamic redox-dependent effects on CD4 membrane domain localization. RESULTS Blocking cell surface redox exchanges with both a membrane-impermeable sulfhydryl blocker (DTNB) and specific antibody inhibitors of Thioredoxin-1 (Trx1) induces translocation of CD4 into detergent-resistant membrane domains (DRM). In contrast, Trx1 inactivation does not change the localization of the chemokine receptor CCR5, suggesting that this effect is targeted. Moreover, DTNB treatment and Trx1 depletion coincide with strong inhibition of CD4-dependent HIV entry, but only moderate reductions in the infectivity of a CD4-independent HIV pseudovirion. CONCLUSIONS Changes in the extracellular redox environment, potentially mediated by allosteric consequences of functional disulfide bond oxidoreduction, may represent a signal for translocation of CD4 into DRM clusters, and this sequestration, another potential mechanism by which the anti-HIV effects of cell surface oxidoreductase inhibition are exerted. GENERAL SIGNIFICANCE Extracellular redox conditions may regulate CD4 function by potentiating changes in its membrane domain localization.
Collapse
Affiliation(s)
- Naazneen Moolla
- HIV Pathogenesis Research Unit, Department of Molecular Medicine and Haematology, University of the Witwatersrand, Faculty of Health Sciences, 7 York Road Parktown, 2193 Johannesburg, South Africa
| | - Mark Killick
- HIV Pathogenesis Research Unit, Department of Molecular Medicine and Haematology, University of the Witwatersrand, Faculty of Health Sciences, 7 York Road Parktown, 2193 Johannesburg, South Africa
| | - Maria Papathanasopoulos
- HIV Pathogenesis Research Unit, Department of Molecular Medicine and Haematology, University of the Witwatersrand, Faculty of Health Sciences, 7 York Road Parktown, 2193 Johannesburg, South Africa
| | - Alexio Capovilla
- HIV Pathogenesis Research Unit, Department of Molecular Medicine and Haematology, University of the Witwatersrand, Faculty of Health Sciences, 7 York Road Parktown, 2193 Johannesburg, South Africa.
| |
Collapse
|