Publications (22)186.52 Total impact
-
Article: Subunit organization of the membrane-bound HIV-1 envelope glycoprotein trimer.
[show abstract] [hide abstract]
ABSTRACT: The trimeric human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (Env) spike is a molecular machine that mediates virus entry into host cells and is the sole target for virus-neutralizing antibodies. The mature Env spike results from cleavage of a trimeric glycoprotein precursor, gp160, into three gp120 and three gp41 subunits. Here, we describe an ~11-Å cryo-EM structure of the trimeric HIV-1 Env precursor in its unliganded state. The three gp120 and three gp41 subunits form a cage-like structure with an interior void surrounding the trimer axis. Interprotomer contacts are limited to the gp41 transmembrane region, the torus-like gp41 ectodomain and a trimer-association domain of gp120 composed of the V1, V2 and V3 variable regions. The cage-like architecture, which is unique among characterized viral envelope proteins, restricts antibody access, reflecting requirements imposed by HIV-1 persistence in the host.Nature Structural & Molecular Biology 08/2012; 19(9):893-9. · 12.71 Impact Factor -
Article: Lineage-specific differences between human and simian immunodeficiency virus regulation of gp120 trimer association and CD4 binding.
[show abstract] [hide abstract]
ABSTRACT: Metastable conformations of the gp120 and gp41 envelope glycoproteins of human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV) must be maintained in the unliganded state of the envelope glycoprotein trimer. Binding of gp120 to the primary receptor, CD4, triggers the transition to an open conformation of the trimer, promoting interaction with the CCR5 chemokine receptor and ultimately leading to gp41-mediated virus-cell membrane fusion and entry. Topological layers in the gp120 inner domain contribute to gp120-trimer association in the unliganded state and to CD4 binding. Here we describe similarities and differences between HIV-1 and SIVmac gp120. In both viruses, the gp120 N/C termini and the inner domain β-sandwich and layer 2 support the noncovalent association of gp120 with the envelope glycoprotein trimer. Layer 1 of the SIVmac gp120 inner domain contributes more to trimer association than the corresponding region of HIV-1 gp120. On the other hand, layer 1 plays an important role in stabilizing the CD4-bound conformation of HIV-1 but not SIVmac gp120 and thus contributes to HIV-1 binding to CD4. In SIVmac, CD4 binding is instead enhanced by tryptophan 375, which fills the Phe 43 cavity of gp120. Activation of SIVmac by soluble CD4 is dependent on tryptophan 375 and on layer 1 residues that determine a tight association of gp120 with the trimer. Distinct biological requirements for CD4 usage have resulted in lineage-specific differences in the HIV-1 and SIV gp120 structures that modulate trimer association and CD4 binding.Journal of Virology 06/2012; 86(17):8974-86. · 5.40 Impact Factor -
Article: Evaluation of competing J domain:Hsp70 complex models in light of existing mutational and NMR data.
[show abstract] [hide abstract]
ABSTRACT: Ahmad et al. recently presented an NMR-based model for a bacterial DnaJ J domain:DnaK(Hsp70):ADP complex(1) that differs significantly from the crystal structure of a disulfide linked mammalian auxilin J domain:Hsc70 complex that we previously published(2). They claimed that their model could better account for existing mutational data, was in better agreement with previous NMR studies, and that the presence of a cross-link in our structure made it irrelevant to understanding J:Hsp70 interactions. Here we detail extensive NMR and mutational data relevant to understanding J:Hsp70 function and show that, in fact, our structure is much better able to account for the mutational data and is in much better agreement with a previous NMR study of a mammalian polyoma virus T-ag J domain:Hsc70 complex than is the Ahmad et al. complex, and that our structure is predictive and provides insight into J:Hsp70 interactions and mechanism of ATPase activation.Proceedings of the National Academy of Sciences 03/2012; 109(13):E734; author reply E735. · 9.68 Impact Factor -
Article: Contribution of intrinsic reactivity of the HIV-1 envelope glycoproteins to CD4-independent infection and global inhibitor sensitivity.
[show abstract] [hide abstract]
ABSTRACT: Human immunodeficiency virus (HIV-1) enters cells following sequential activation of the high-potential-energy viral envelope glycoprotein trimer by target cell CD4 and coreceptor. HIV-1 variants differ in their requirements for CD4; viruses that can infect coreceptor-expressing cells that lack CD4 have been generated in the laboratory. These CD4-independent HIV-1 variants are sensitive to neutralization by multiple antibodies that recognize different envelope glycoprotein epitopes. The mechanisms underlying CD4 independence, global sensitivity to neutralization and the association between them are still unclear. By studying HIV-1 variants that differ in requirements for CD4, we investigated the contribution of CD4 binding to virus entry. CD4 engagement exposes the coreceptor-binding site and increases the "intrinsic reactivity" of the envelope glycoproteins; intrinsic reactivity describes the propensity of the envelope glycoproteins to negotiate transitions to lower-energy states upon stimulation. Coreceptor-binding site exposure and increased intrinsic reactivity promote formation/exposure of the HR1 coiled coil on the gp41 transmembrane glycoprotein and allow virus entry upon coreceptor binding. Intrinsic reactivity also dictates the global sensitivity of HIV-1 to perturbations such as exposure to cold and the binding of antibodies and small molecules. Accordingly, CD4 independence of HIV-1 was accompanied by increased susceptibility to inactivation by these factors. We investigated the role of intrinsic reactivity in determining the sensitivity of primary HIV-1 isolates to inhibition. Relative to the more common neutralization-resistant ("Tier 2-like") viruses, globally sensitive ("Tier 1") viruses exhibited increased intrinsic reactivity, i.e., were inactivated more efficiently by cold exposure or by a given level of antibody binding to the envelope glycoprotein trimer. Virus sensitivity to neutralization was dictated both by the efficiency of inhibitor/antibody binding to the envelope glycoprotein trimer and by envelope glycoprotein reactivity to the inhibitor/antibody binding event. Quantitative differences in intrinsic reactivity contribute to HIV-1 strain variability in global susceptibility to neutralization and explain the long-observed relationship between increased inhibitor sensitivity and decreased entry requirements for target cell CD4.PLoS Pathogens 06/2011; 7(6):e1002101. · 9.13 Impact Factor -
Article: Topological layers in the HIV-1 gp120 inner domain regulate gp41 interaction and CD4-triggered conformational transitions.
[show abstract] [hide abstract]
ABSTRACT: The entry of human immunodeficiency virus (HIV-1) into cells is initiated by binding of the gp120 exterior envelope glycoprotein to the receptor, CD4. How does CD4 binding trigger conformational changes in gp120 that allow the gp41 transmembrane envelope glycoprotein to mediate viral-cell membrane fusion? The transition from the unliganded to the CD4-bound state is regulated by two potentially flexible topological layers (layers 1 and 2) in the gp120 inner domain. Both layers apparently contribute to the noncovalent association of unliganded gp120 with gp41. After CD4 makes initial contact with the gp120 outer domain, layer 1-layer 2 interactions strengthen gp120-CD4 binding by reducing the off rate. Layer 1-layer 2 interactions also destabilize the activated state induced on HIV-1 by treatment with soluble CD4. Thus, despite lack of contact with CD4, the gp120 inner-domain layers govern CD4 triggering by participating in conformational transitions within gp120 and regulating the interaction with gp41.Molecular cell 03/2010; 37(5):656-67. · 14.61 Impact Factor -
Article: Thermal stability of the human immunodeficiency virus type 1 (HIV-1) receptors, CD4 and CXCR4, reconstituted in proteoliposomes.
[show abstract] [hide abstract]
ABSTRACT: The entry of human immunodeficiency virus (HIV-1) into host cells involves the interaction of the viral exterior envelope glycoprotein, gp120, and receptors on the target cell. The HIV-1 receptors are CD4 and one of two chemokine receptors, CCR5 or CXCR4. We created proteoliposomes that contain CD4, the primary HIV-1 receptor, and one of the coreceptors, CXCR4. Antibodies against CD4 and CXCR4 specifically bound the proteoliposomes. CXCL12, the natural ligand for CXCR4, and the small-molecule CXCR4 antagonist, AMD3100, bound the proteoliposomes with affinities close to those associated with the binding of these molecules to cells expressing CXCR4 and CD4. The HIV-1 gp120 exterior envelope glycoprotein bound tightly to proteoliposomes expressing only CD4 and, in the presence of soluble CD4, bound weakly to proteoliposomes expressing only CXCR4. The thermal stability of CD4 and CXCR4 inserted into liposomes was examined. Thermal denaturation of CXCR4 followed second-order kinetics, with an activation energy (E(a)) of 269 kJ/mol (64.3 kcal/mol) and an inactivation temperature (T(i)) of 56°C. Thermal inactivation of CD4 exhibited a reaction order of 1.3, an E(a) of 278 kJ/mol (66.5 kcal/mol), and a T(i) of 52.2°C. The second-order denaturation kinetics of CXCR4 is unusual among G protein-coupled receptors, and may result from dimeric interactions between CXCR4 molecules. Our studies with proteoliposomes containing the native HIV-1 receptors allowed an examination of the binding of biologically important ligands and revealed the higher-order denaturation kinetics of these receptors. CD4/CXCR4-proteoliposomes may be useful for the study of virus-target cell interactions and for the identification of inhibitors.PLoS ONE 01/2010; 5(10):e13249. · 4.09 Impact Factor -
Article: Transitions to and from the CD4-bound conformation are modulated by a single-residue change in the human immunodeficiency virus type 1 gp120 inner domain.
[show abstract] [hide abstract]
ABSTRACT: Binding to the primary receptor CD4 induces conformational changes in the human immunodeficiency virus type 1 (HIV-1) gp120 envelope glycoprotein that allow binding to the coreceptor (CCR5 or CXCR4) and ultimately trigger viral membrane-cell membrane fusion mediated by the gp41 transmembrane envelope glycoprotein. Here we report the derivation of an HIV-1 gp120 variant, H66N, that confers envelope glycoprotein resistance to temperature extremes. The H66N change decreases the spontaneous sampling of the CD4-bound conformation by the HIV-1 envelope glycoproteins, thus diminishing CD4-independent infection. The H66N change also stabilizes the HIV-1 envelope glycoprotein complex once the CD4-bound state is achieved, decreasing the probability of CD4-induced inactivation and revealing the enhancing effects of soluble CD4 binding on HIV-1 infection. In the CD4-bound conformation, the highly conserved histidine 66 is located between the receptor-binding and gp41-interactive surfaces of gp120. Thus, a single amino acid change in this strategically positioned gp120 inner domain residue influences the propensity of the HIV-1 envelope glycoproteins to negotiate conformational transitions to and from the CD4-bound state.Journal of Virology 07/2009; 83(17):8364-78. · 5.40 Impact Factor -
Article: Soluble CD4 and CD4-mimetic compounds inhibit HIV-1 infection by induction of a short-lived activated state.
[show abstract] [hide abstract]
ABSTRACT: Binding to the CD4 receptor induces conformational changes in the human immunodeficiency virus (HIV-1) gp120 exterior envelope glycoprotein. These changes allow gp120 to bind the coreceptor, either CCR5 or CXCR4, and prime the gp41 transmembrane envelope glycoprotein to mediate virus-cell membrane fusion and virus entry. Soluble forms of CD4 (sCD4) and small-molecule CD4 mimics (here exemplified by JRC-II-191) also induce these conformational changes in the HIV-1 envelope glycoproteins, but typically inhibit HIV-1 entry into CD4-expressing cells. To investigate the mechanism of inhibition, we monitored at high temporal resolution inhibitor-induced changes in the conformation and functional competence of the HIV-1 envelope glycoproteins that immediately follow engagement of the soluble CD4 mimics. Both sCD4 and JRC-II-191 efficiently activated the envelope glycoproteins to mediate infection of cells lacking CD4, in a manner dependent on coreceptor affinity and density. This activated state, however, was transient and was followed by spontaneous and apparently irreversible changes of conformation and by loss of functional competence. The longevity of the activated intermediate depended on temperature and the particular HIV-1 strain, but was indistinguishable for sCD4 and JRC-II-191; by contrast, the activated intermediate induced by cell-surface CD4 was relatively long-lived. The inactivating effects of these activation-based inhibitors predominantly affected cell-free virus, whereas virus that was prebound to the target cell surface was mainly activated, infecting the cells even at high concentrations of the CD4 analogue. These results demonstrate the ability of soluble CD4 mimics to inactivate HIV-1 by prematurely triggering active but transient intermediate states of the envelope glycoproteins. This novel strategy for inhibition may be generally applicable to high-potential-energy viral entry machines that are normally activated by receptor binding.PLoS Pathogens 05/2009; 5(4):e1000360. · 9.13 Impact Factor -
Article: Small-molecule CD4 mimics interact with a highly conserved pocket on HIV-1 gp120.
[show abstract] [hide abstract]
ABSTRACT: Human immunodeficiency virus (HIV-1) interaction with the primary receptor, CD4, induces conformational changes in the viral envelope glycoproteins that allow binding to the CCR5 second receptor and virus entry into the host cell. The small molecule NBD-556 mimics CD4 by binding the gp120 exterior envelope glycoprotein, moderately inhibiting virus entry into CD4-expressing target cells and enhancing CCR5 binding and virus entry into CCR5-expressing cells lacking CD4. Studies of NBD-556 analogs and gp120 mutants suggest that (1) NBD-556 binds within the Phe 43 cavity, a highly conserved, functionally important pocket formed as gp120 assumes the CD4-bound conformation; (2) the NBD-556 phenyl ring projects into the Phe 43 cavity; (3) enhancement of CD4-independent infection by NBD-556 requires the induction of conformational changes in gp120; and (4) increased affinity of NBD-556 analogs for gp120 improves antiviral potency during infection of CD4-expressing cells.Structure 12/2008; 16(11):1689-701. · 6.35 Impact Factor -
Article: Antibody binding in proximity to the receptor/glycoprotein complex leads to a basal level of virus neutralization.
[show abstract] [hide abstract]
ABSTRACT: Hypothetically, antibodies may neutralize enveloped viruses by diverse mechanisms, such as disruption of receptor binding, interference with conformational changes required for virus entry, steric hindrance, or virus aggregation. Here, we demonstrate that retroviral infection mediated by the avian sarcoma-leukosis virus (ASLV-A) envelope glycoproteins can be neutralized by an antibody directed against a functionally unimportant component of a chimeric receptor protein. Thus, the binding of an antibody in proximity to the retroviral envelope glycoprotein-receptor complex, without binding to the entry machinery itself, results in neutralization. This finding provides additional support for the hypothesis that steric hindrance is sufficient for antibody-mediated neutralization of retroviruses.Journal of Virology 09/2007; 81(16):8809-13. · 5.40 Impact Factor -
Article: Functional mimicry of a human immunodeficiency virus type 1 coreceptor by a neutralizing monoclonal antibody.
[show abstract] [hide abstract]
ABSTRACT: Interaction of the human immunodeficiency virus type 1 (HIV-1) gp120 envelope glycoprotein with the primary receptor, CD4, promotes binding to a chemokine receptor, either CCR5 or CXCR4. The chemokine receptor-binding site on gp120 elicits CD4-induced (CD4i) antibodies in some HIV-1-infected individuals. Like CCR5 itself, the CD4i antibody 412d exhibits a preference for CCR5-using HIV-1 strains and utilizes sulfated tyrosines to achieve binding to gp120. Here, we show that 412d binding requires the gp120 beta19 strand and the base of the V3 loop, elements that are important for the binding of the CCR5 N terminus. Two gp120 residues in the V3 loop base determined 412d preference for CCR5-using HIV-1 strains. A chimeric molecule in which the 412d heavy-chain third complementarity-determining loop sequence replaces the CCR5 N terminus functioned as an efficient second receptor, selectively supporting the entry of CCR5-using HIV-1 strains. Sulfation of N-terminal tyrosines contributed to the function of this chimeric receptor. These results emphasize the close mimicry of the CCR5 N terminus by the gp120-interactive region of a naturally elicited CD4i antibody.Journal of Virology 06/2005; 79(10):6068-77. · 5.40 Impact Factor -
Article: Characterization of the outer domain of the gp120 glycoprotein from human immunodeficiency virus type 1.
[show abstract] [hide abstract]
ABSTRACT: The core of the gp120 glycoprotein from human immunodeficiency virus type 1 (HIV-1) is comprised of three major structural domains: the outer domain, the inner domain, and the bridging sheet. The outer domain is exposed on the HIV-1 envelope glycoprotein trimer and contains binding surfaces for neutralizing antibodies such as 2G12, immunoglobulin G1b12, and anti-V3 antibodies. We expressed the outer domain of HIV-1(YU2) gp120 as an independent protein, termed OD1. OD1 efficiently bound 2G12 and a large number of anti-V3 antibodies, indicating its structural integrity. Immunochemical studies with OD1 indicated that antibody responses against the outer domain of the HIV-1 gp120 envelope glycoprotein are rare in HIV-1-infected human sera that potently neutralize the virus. Surprisingly, such outer-domain-directed antibody responses are commonly elicited by immunization with recombinant monomeric gp120. Immunization with soluble, stabilized HIV-1 envelope glycoprotein trimers elicited antibody responses that more closely resembled those in the sera of HIV-1-infected individuals. These results underscore the qualitatively different humoral immune responses elicited during natural infection and after gp120 vaccination and help to explain the failure of gp120 as an effective vaccine.Journal of Virology 01/2005; 78(23):12975-86. · 5.40 Impact Factor -
Article: Neutralization sensitivity of a simian-human immunodeficiency virus (SHIV-HXBc2P 3.2N) isolated from an infected rhesus macaque with neurological disease.
[show abstract] [hide abstract]
ABSTRACT: Simian-human immunodeficiency virus (SHIV) chimerae, after in vivo passage in monkeys, can induce acquired immunodeficiency syndrome (AIDS)-like illness and death. A monkey infected with the molecularly cloned, pathogenic SHIV-HXBc2P 3.2 exhibited multifocal granulomatous pneumonia as well as progressive neurological impairment characterized by tremors and pelvic limb weakness. SHIV-HXBc2P 3.2N was isolated from brain tissue explants and characterized. Viruses with the envelope glycoproteins of SHIV-HXBc2P 3.2N exhibited increased sensitivity to soluble CD4 and several neutralizing antibodies compared with viruses with the parental SHIV-HXBc2P 3.2 envelope glycoproteins. By contrast, viruses with SHIV-HXBc2P 3.2 and SHIV-HXBc2P 3.2N envelope glycoproteins were neutralized equivalently by 2G12 and 2F5 antibodies, which are rarely elicited in HIV-1-infected humans. A constellation of changes involving both gp120 and gp41 envelope glycoproteins was responsible for the difference in susceptibility to neutralization by most antibodies. Surprisingly, the gain of an N-linked glycosylation site in the gp41 ectodomain contributed greatly to neutralization sensitivity. Thus, the environment of the central nervous system, particularly in the context of immunodeficiency, allows the evolution of immunodeficiency viruses with greater susceptibility to neutralization by antibodies.Virology 05/2004; 322(1):168-81. · 3.35 Impact Factor -
Article: Small-molecule inhibitors of HIV-1 entry block receptor-induced conformational changes in the viral envelope glycoproteins.
[show abstract] [hide abstract]
ABSTRACT: When interacting with the CD4 receptor, the HIV gp120 envelope glycoprotein undergoes conformational changes that allow binding to the chemokine receptor. Receptor binding is proposed to lead to conformational changes in the gp41 transmembrane envelope glycoprotein involving the creation and/or exposure of a coiled coil consisting of three heptad repeat (HR) sequences. The subsequent interaction of the HR2 region of gp41 with this coiled coil results in the assembly of a six-helix bundle that promotes the fusion of the viral and target cell membranes. Here we show that CD4 binding to gp120 induces the formation and/or exposure of the gp41 HR1 coiled coil in a process that does not involve gp120 shedding and that depends on the proteolytic maturation of the gp160 envelope glycoprotein precursor. Importantly, BMS-806 and related HIV-1 entry inhibitors bind gp120 and block the CD4 induction of HR1 exposure without significantly affecting CD4 binding. Moreover, these compounds do not disrupt gp120-chemokine receptor binding or the HR1-HR2 interaction within gp41. These studies thus define a receptor-induced conformational rearrangement of gp120-gp41 that is important for both CD4-dependent and CD4-independent HIV-1 entry and is susceptible to inhibition by low-molecular-weight compounds.Proceedings of the National Academy of Sciences 05/2004; 101(14):5036-41. · 9.68 Impact Factor -
Article: Epitope mapping and characterization of a novel CD4-induced human monoclonal antibody capable of neutralizing primary HIV-1 strains.
[show abstract] [hide abstract]
ABSTRACT: Human immunodeficiency virus (HIV-1) enters target cells by binding its gp120 exterior envelope glycoprotein to CD4 and one of the chemokine receptors, CCR5 or CXCR4. CD4-induced (CD4i) antibodies bind gp120 more efficiently after CD4 binding and block the interaction with the chemokine receptor. Examples of CD4i antibodies are limited, and the prototypes of the CD4i antibodies exhibit only weak neutralizing activity against primary, clinical HIV-1 isolates. Here we report the identification of a novel antibody, E51, that exhibits CD4-induced binding to gp120 and neutralizes primary HIV-1 more efficiently than the prototypic CD4i antibodies. The E51 antibody blocks the interaction of gp120-CD4 complexes with CCR5 and binds to a highly conserved, basic gp120 element composed of the beta 19-strand and surrounding structures. Thus, on primary HIV-1 isolates, this gp120 region, which has been previously implicated in chemokine receptor binding, is accessible to a subset of CD4i antibodies.Virology 11/2003; 315(1):124-34. · 3.35 Impact Factor -
Article: Structure-based, targeted deglycosylation of HIV-1 gp120 and effects on neutralization sensitivity and antibody recognition.
[show abstract] [hide abstract]
ABSTRACT: The human immunodeficiency virus (HIV-1) exterior envelope glycoprotein, gp120, mediates receptor binding and is the major target for neutralizing antibodies. Primary HIV-1 isolates are characteristically more resistant to broadly neutralizing antibodies, although the structural basis for this resistance remains obscure. Most broadly neutralizing antibodies are directed against functionally conserved gp120 regions involved in binding to either the primary virus receptor, CD4, or the viral coreceptor molecules that normally function as chemokine receptors. These antibodies are known as CD4 binding site (CD4BS) and CD4-induced (CD4i) antibodies, respectively. Inspection of the gp120 crystal structure reveals that although the receptor-binding regions lack glycosylation, sugar moieties lie proximal to both receptor-binding sites on gp120 and thus in proximity to both the CD4BS and the CD4i epitopes. In this study, guided by the X-ray crystal structure of gp120, we deleted four N-linked glycosylation sites that flank the receptor-binding regions. We examined the effects of selected changes on the sensitivity of two prototypic HIV-1 primary isolates to neutralization by antibodies. Surprisingly, removal of a single N-linked glycosylation site at the base of the gp120 third variable region (V3 loop) increased the sensitivity of the primary viruses to neutralization by CD4BS antibodies. Envelope glycoprotein oligomers on the cell surface derived from the V3 glycan-deficient virus were better recognized by a CD4BS antibody and a V3 loop antibody than were the wild-type glycoproteins. Absence of all four glycosylation sites rendered a primary isolate sensitive to CD4i antibody-mediated neutralization. Thus, carbohydrates that flank receptor-binding regions on gp120 protect primary HIV-1 isolates from antibody-mediated neutralization.Virology 10/2003; 313(2):387-400. · 3.35 Impact Factor -
Article: Tyrosine sulfation of human antibodies contributes to recognition of the CCR5 binding region of HIV-1 gp120.
[show abstract] [hide abstract]
ABSTRACT: Sulfated tyrosines at the amino terminus of the principal HIV-1 coreceptor CCR5 play a critical role in its ability to bind the HIV-1 envelope glycoprotein gp120 and mediate HIV-1 infection. Here, we show that a number of human antibodies directed against gp120 are tyrosine sulfated at their antigen binding sites. Like that of CCR5, antibody association with gp120 is dependent on sulfate moieties, enhanced by CD4, and inhibited by sulfated CCR5-derived peptides. Most of these antibodies preferentially associate with gp120 molecules of CCR5-utilizing (R5) isolates and neutralize primary R5 isolates more efficiently than laboratory-adapted isolates. These studies identify a distinct subset of CD4-induced HIV-1 neutralizing antibodies that closely emulate CCR5 and demonstrate that tyrosine sulfation can contribute to the potency and diversity of the human humoral response.Cell 08/2003; 114(2):161-70. · 32.40 Impact Factor -
Article: HIV-1 evades antibody-mediated neutralization through conformational masking of receptor-binding sites.
[show abstract] [hide abstract]
ABSTRACT: The ability of human immunodeficiency virus (HIV-1) to persist and cause AIDS is dependent on its avoidance of antibody-mediated neutralization. The virus elicits abundant, envelope-directed antibodies that have little neutralization capacity. This lack of neutralization is paradoxical, given the functional conservation and exposure of receptor-binding sites on the gp120 envelope glycoprotein, which are larger than the typical antibody footprint and should therefore be accessible for antibody binding. Because gp120-receptor interactions involve conformational reorganization, we measured the entropies of binding for 20 gp120-reactive antibodies. Here we show that recognition by receptor-binding-site antibodies induces conformational change. Correlation with neutralization potency and analysis of receptor-antibody thermodynamic cycles suggested a receptor-binding-site 'conformational masking' mechanism of neutralization escape. To understand how such an escape mechanism would be compatible with virus-receptor interactions, we tested a soluble dodecameric receptor molecule and found that it neutralized primary HIV-1 isolates with great potency, showing that simultaneous binding of viral envelope glycoproteins by multiple receptors creates sufficient avidity to compensate for such masking. Because this solution is available for cell-surface receptors but not for most antibodies, conformational masking enables HIV-1 to maintain receptor binding and simultaneously to resist neutralization.Nature 01/2003; 420(6916):678-82. · 36.28 Impact Factor -
Article: Mutagenic stabilization and/or disruption of a CD4-bound state reveals distinct conformations of the human immunodeficiency virus type 1 gp120 envelope glycoprotein.
[show abstract] [hide abstract]
ABSTRACT: The human immunodeficiency virus type 1 (HIV-1) gp120 exterior envelope glycoprotein is conformationally flexible. Upon binding to the host cell receptor CD4, gp120 assumes a conformation that is recognized by the second receptor, CCR5 and/or CXCR4, and by the CD4-induced (CD4i) antibodies. Guided by the X-ray crystal structure of a gp120-CD4-CD4i antibody complex, we introduced changes into gp120 that were designed to stabilize or disrupt this conformation. One mutant, 375 S/W, in which the tryptophan indole group is predicted to occupy the Phe 43 cavity in the gp120 interior, apparently favors a gp120 conformation closer to that of the CD4-bound state. The 375 S/W mutant was recognized as well as or better than wild-type gp120 by CD4 and CD4i antibodies, and the large decrease in entropy observed when wild-type gp120 bound CD4 was reduced for the 375 S/W mutant. The recognition of the 375 S/W mutant by CD4BS antibodies, which are directed against the CD4-binding region of gp120, was markedly reduced compared with that of the wild-type gp120. Compared with the wild-type virus, viruses with the 375 S/W envelope glycoproteins were resistant to neutralization by IgG1b12, a CD4BS antibody, were slightly more sensitive to soluble CD4 neutralization and were neutralized more efficiently by the 2G12 antibody. Another mutant, 423 I/P, in which the gp120 bridging sheet was disrupted, did not bind CD4, CCR5, or CD4i antibodies, even though recognition by CD4BS antibodies was efficient. These results indicate that CD4BS antibodies recognize conformations of gp120 different from that recognized by CD4 and CD4i antibodies.Journal of Virology 11/2002; 76(19):9888-99. · 5.40 Impact Factor -
Article: Impacts of HAB species Heterosigma akashiwo on early development of the scallop Argopecten irradians Lamarck
[show abstract] [hide abstract]
ABSTRACT: The effects of Heterosigma akashiwo on the early development of Argopecten irradians Lamarck: eggs, D-shaped larvae, eye-spot larvae and juveniles, were investigated under laboratory conditions. Exposing fertilized eggs to various densities of H. akashiwo algal culture revealed that the development of the embryos to the gastrula was significantly slowed at densities of more than 1 × 104 cells/ml algal cells, and mostly was arrested when the embryos reached the trochophore larvae stage. At this stage, several trochophore larvae were adhered together by the algal cells, resulting in the inhibition of their swimming activity. Larvae had still not developed into D-shaped larvae after 30 h, and therefore did not finish the hatching process. The attachment and adherence of the algal cells to the larvae might be an important process in the mechanism of the impact on egg hatching success.The activity of the D-shaped larvae was significantly inhibited after 48 h exposure to H. akashiwo at a density of 15 × 104 cells/ml and after 96 h at 10 × 104 cells/ml. The survival rate of the eye-spot larvae was decreased significantly after 48 h exposure to the algal culture at densities of more than 1 × 104 cells/ml. However, all the juveniles could survive and their climbing and attachment activity were not affected after 1 and 5 h exposure to the algal culture at all the various algal cell densities tested from 5 to 20 × 104 cells/ml.The results indicated that susceptibility of embryos or larvae to the alga H. akashiwo differs depending on the developmental stage. The embryos and the eye-spot larvae of A. irradians are more sensitive stages to the toxicity of H. akashiwo. Observed effects of H. akashiwo exposure on early development of A. irradians serve to point out to the potential danger of this alga for scallop populations. The possible toxicological mechanisms of H. akashiwo on the scallop embryos and larvae are discussed.Aquaculture.
Top co-authors
Top Journals
Institutions
-
2002–2012
-
Dana-Farber Cancer Institute
- Department of Cancer Immunology and AIDS
Boston, MA, USA
-
-
2007
-
Beth Israel Deaconess Medical Center
- Division of Viral Pathogenesis
Boston, MA, USA
-
