1
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Gupta M, Canziani G, Ang C, Mohammadi M, Abrams CF, Yang D, Smith AB, Chaiken I. Pharmacophore Variants of the Macrocyclic Peptide Triazole Inactivator of HIV-1 Env. RESEARCH SQUARE 2023:rs.3.rs-2814722. [PMID: 37131733 PMCID: PMC10153383 DOI: 10.21203/rs.3.rs-2814722/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Previously we established a family of macrocyclic peptide triazoles (cPTs) that inactivate the Env protein complex of HIV-1, and identified the pharmacophore that engages Env's receptor binding pocket. Here, we examined the hypothesis that the side chains of both components of the triazole Pro - Trp segment of cPT pharmacophore work in tandem to make intimate contacts with two proximal subsites of the overall CD4 binding site of gp120 to stabilize binding and function. Variations of the triazole Pro R group, which previously had been significantly optimized, led to identification of a variant MG-II-20 that contains a pyrazole substitution. MG-II-20 has improved functional properties over previously examined variants, with Kd for gp120 in the nM range. In contrast, new variants of the Trp indole side chain, with either methyl- or bromo- components appended, had disruptive effects on gp120 binding, reflecting the sensitivity of function to changes in this component of the encounter complex. Plausible in silico models of cPT:gp120 complex structures were obtained that are consistent with the overall hypothesisof occupancy by the triazole Pro and Trp side chains, respectively, into the β20/21 and Phe43 sub-cavities. The overall results strengthen the definition of the cPT-Env inactivator binding site and provide a new lead composition (MG-II-20) as well as structure-function findings to guide future HIV-1 Env inactivator design.
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Affiliation(s)
- Monisha Gupta
- Department of Biochemistry and Molecular Biology, College of Medicine, Drexel University, Philadelphia, Pennsylvania 19102, United States
- Department of Chemistry, College of Arts and Sciences, Drexel University, Philadelphia, Pennsylvania 19102, United States
| | - Gabriela Canziani
- Department of Biochemistry and Molecular Biology, College of Medicine, Drexel University, Philadelphia, Pennsylvania 19102, United States
| | - Charles Ang
- Department of Biochemistry and Molecular Biology, College of Medicine, Drexel University, Philadelphia, Pennsylvania 19102, United States
| | - Mohammadjavad Mohammadi
- Department of Chemical & Biological Engineering, College of Engineering, Drexel University, Philadelphia, Pennsylvania 19102, United States
| | - Cameron F Abrams
- Department of Chemical & Biological Engineering, College of Engineering, Drexel University, Philadelphia, Pennsylvania 19102, United States
| | - Derek Yang
- Department of Chemistry, School of Arts and Sciences, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Amos B Smith
- Department of Chemistry, School of Arts and Sciences, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Irwin Chaiken
- Department of Biochemistry and Molecular Biology, College of Medicine, Drexel University, Philadelphia, Pennsylvania 19102, United States
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2
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Mohamed H, Gurrola T, Berman R, Collins M, Sariyer IK, Nonnemacher MR, Wigdahl B. Targeting CCR5 as a Component of an HIV-1 Therapeutic Strategy. Front Immunol 2022; 12:816515. [PMID: 35126374 PMCID: PMC8811197 DOI: 10.3389/fimmu.2021.816515] [Citation(s) in RCA: 19] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2021] [Accepted: 12/13/2021] [Indexed: 12/26/2022] Open
Abstract
Globally, human immunodeficiency virus type 1 (HIV-1) infection is a major health burden for which successful therapeutic options are still being investigated. Challenges facing current drugs that are part of the established life-long antiretroviral therapy (ART) include toxicity, development of drug resistant HIV-1 strains, the cost of treatment, and the inability to eradicate the provirus from infected cells. For these reasons, novel anti-HIV-1 therapeutics that can prevent or eliminate disease progression including the onset of the acquired immunodeficiency syndrome (AIDS) are needed. While development of HIV-1 vaccination has also been challenging, recent advancements demonstrate that infection of HIV-1-susceptible cells can be prevented in individuals living with HIV-1, by targeting C-C chemokine receptor type 5 (CCR5). CCR5 serves many functions in the human immune response and is a co-receptor utilized by HIV-1 for entry into immune cells. Therapeutics targeting CCR5 generally involve gene editing techniques including CRISPR, CCR5 blockade using antibodies or antagonists, or combinations of both. Here we review the efficacy of these approaches and discuss the potential of their use in the clinic as novel ART-independent therapies for HIV-1 infection.
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Affiliation(s)
- Hager Mohamed
- Department of Microbiology and Immunology, Center for Molecular Virology and Translational Neuroscience, Institute for Molecular Medicine and Infectious Disease, Drexel University College of Medicine, Philadelphia, PA, United States
| | - Theodore Gurrola
- Department of Microbiology and Immunology, Center for Molecular Virology and Translational Neuroscience, Institute for Molecular Medicine and Infectious Disease, Drexel University College of Medicine, Philadelphia, PA, United States
| | - Rachel Berman
- Department of Microbiology and Immunology, Center for Molecular Virology and Translational Neuroscience, Institute for Molecular Medicine and Infectious Disease, Drexel University College of Medicine, Philadelphia, PA, United States
| | - Mackenzie Collins
- Department of Microbiology and Immunology, Center for Molecular Virology and Translational Neuroscience, Institute for Molecular Medicine and Infectious Disease, Drexel University College of Medicine, Philadelphia, PA, United States
| | - Ilker K. Sariyer
- Department of Microbiology, Immunology, and Inflammation, Center for Neurovirology and Gene Editing, School of Medicine, Temple University, Philadelphia, PA, United States
| | - Michael R. Nonnemacher
- Department of Microbiology and Immunology, Center for Molecular Virology and Translational Neuroscience, Institute for Molecular Medicine and Infectious Disease, Drexel University College of Medicine, Philadelphia, PA, United States
| | - Brian Wigdahl
- Department of Microbiology and Immunology, Center for Molecular Virology and Translational Neuroscience, Institute for Molecular Medicine and Infectious Disease, Drexel University College of Medicine, Philadelphia, PA, United States
- *Correspondence: Brian Wigdahl,
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3
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Zhang S, Holmes AP, Dick A, Rashad AA, Enríquez Rodríguez L, Canziani GA, Root MJ, Chaiken IM. Altered Env conformational dynamics as a mechanism of resistance to peptide-triazole HIV-1 inactivators. Retrovirology 2021; 18:31. [PMID: 34627310 PMCID: PMC8501640 DOI: 10.1186/s12977-021-00575-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2021] [Accepted: 09/20/2021] [Indexed: 12/28/2022] Open
Abstract
BACKGROUND We previously developed drug-like peptide triazoles (PTs) that target HIV-1 Envelope (Env) gp120, potently inhibit viral entry, and irreversibly inactivate virions. Here, we investigated potential mechanisms of viral escape from this promising class of HIV-1 entry inhibitors. RESULTS HIV-1 resistance to cyclic (AAR029b) and linear (KR13) PTs was obtained by dose escalation in viral passaging experiments. High-level resistance for both inhibitors developed slowly (relative to escape from gp41-targeted C-peptide inhibitor C37) by acquiring mutations in gp120 both within (Val255) and distant to (Ser143) the putative PT binding site. The similarity in the resistance profiles for AAR029b and KR13 suggests that the shared IXW pharmacophore provided the primary pressure for HIV-1 escape. In single-round infectivity studies employing recombinant virus, V255I/S143N double escape mutants reduced PT antiviral potency by 150- to 3900-fold. Curiously, the combined mutations had a much smaller impact on PT binding affinity for monomeric gp120 (four to ninefold). This binding disruption was entirely due to the V255I mutation, which generated few steric clashes with PT in molecular docking. However, this minor effect on PT affinity belied large, offsetting changes to association enthalpy and entropy. The escape mutations had negligible effect on CD4 binding and utilization during entry, but significantly altered both binding thermodynamics and inhibitory potency of the conformationally-specific, anti-CD4i antibody 17b. Moreover, the escape mutations substantially decreased gp120 shedding induced by either soluble CD4 or AAR029b. CONCLUSIONS Together, the data suggest that the escape mutations significantly modified the energetic landscape of Env's prefusogenic state, altering conformational dynamics to hinder PT-induced irreversible inactivation of Env. This work therein reveals a unique mode of virus escape for HIV-1, namely, resistance by altering the intrinsic conformational dynamics of the Env trimer.
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Affiliation(s)
- Shiyu Zhang
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, PA, USA
- School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, PA, USA
| | - Andrew P Holmes
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, PA, USA
- Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Alexej Dick
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Adel A Rashad
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, PA, USA
| | | | - Gabriela A Canziani
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Michael J Root
- Department of Microbial Infection and Immunity, The Ohio State University College of Medicine, OH, Columbus, USA.
| | - Irwin M Chaiken
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, PA, USA.
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4
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Ang CG, Carter E, Haftl A, Zhang S, Rashad AA, Kutzler M, Abrams CF, Chaiken IM. Peptide Triazole Thiol Irreversibly Inactivates Metastable HIV-1 Env by Accessing Conformational Triggers Intrinsic to Virus-Cell Entry. Microorganisms 2021; 9:1286. [PMID: 34204725 PMCID: PMC8231586 DOI: 10.3390/microorganisms9061286] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2021] [Revised: 06/03/2021] [Accepted: 06/09/2021] [Indexed: 11/16/2022] Open
Abstract
KR13, a peptide triazole thiol previously established to inhibit HIV-1 infection and cause virus lysis, was evaluated by flow cytometry against JRFL Env-presenting cells to characterize induced Env and membrane transformations leading to irreversible inactivation. Transiently transfected HEK293T cells were preloaded with calcein dye, treated with KR13 or its thiol-blocked analogue KR13b, fixed, and stained for gp120 (35O22), MPER (10E8), 6-helix-bundle (NC-1), immunodominant loop (50-69), and fusion peptide (VRC34.01). KR13 induced dose-dependent transformations of Env and membrane characterized by transient poration, MPER exposure, and 6-helix-bundle formation (analogous to native fusion events), but also reduced immunodominant loop and fusion peptide exposure. Using a fusion peptide mutant (V504E), we found that KR13 transformation does not require functional fusion peptide for poration. In contrast, simultaneous treatment with fusion inhibitor T20 alongside KR13 prevented membrane poration and MPER exposure, showing that these events require 6-helix-bundle formation. Based on these results, we formulated a model for PTT-induced Env transformation portraying how, in the absence of CD4/co-receptor signaling, PTT may provide alternate means of perturbing the metastable Env-membrane complex, and inducing fusion-like transformation. In turn, the results show that such transformations are intrinsic to Env and can be diverted for irreversible inactivation of the protein complex.
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Affiliation(s)
- Charles Gotuaco Ang
- Department of Biochemistry and Molecular Biology, College of Medicine, Drexel University, Philadelphia, PA 19102, USA; (E.C.); (A.H.); (S.Z.); (A.A.R.)
- School of Biomedical Engineering, Science, and Health Systems, Drexel University, Philadelphia, PA 19102, USA
| | - Erik Carter
- Department of Biochemistry and Molecular Biology, College of Medicine, Drexel University, Philadelphia, PA 19102, USA; (E.C.); (A.H.); (S.Z.); (A.A.R.)
- Departments of Medicine and Microbiology and Immunology, College of Medicine, Drexel University, Philadelphia, PA 19102, USA;
| | - Ann Haftl
- Department of Biochemistry and Molecular Biology, College of Medicine, Drexel University, Philadelphia, PA 19102, USA; (E.C.); (A.H.); (S.Z.); (A.A.R.)
- Department of Chemistry, College of Arts and Sciences, Drexel University, Philadelphia, PA 19102, USA
| | - Shiyu Zhang
- Department of Biochemistry and Molecular Biology, College of Medicine, Drexel University, Philadelphia, PA 19102, USA; (E.C.); (A.H.); (S.Z.); (A.A.R.)
- School of Biomedical Engineering, Science, and Health Systems, Drexel University, Philadelphia, PA 19102, USA
| | - Adel A. Rashad
- Department of Biochemistry and Molecular Biology, College of Medicine, Drexel University, Philadelphia, PA 19102, USA; (E.C.); (A.H.); (S.Z.); (A.A.R.)
| | - Michele Kutzler
- Departments of Medicine and Microbiology and Immunology, College of Medicine, Drexel University, Philadelphia, PA 19102, USA;
| | - Cameron F. Abrams
- Department of Chemical and Biological Engineering, College of Engineering, Drexel University, Philadelphia, PA 19102, USA;
| | - Irwin M. Chaiken
- Department of Biochemistry and Molecular Biology, College of Medicine, Drexel University, Philadelphia, PA 19102, USA; (E.C.); (A.H.); (S.Z.); (A.A.R.)
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5
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Mirza MU, Saadabadi A, Vanmeert M, Salo-Ahen OMH, Abdullah I, Claes S, De Jonghe S, Schols D, Ahmad S, Froeyen M. Discovery of HIV entry inhibitors via a hybrid CXCR4 and CCR5 receptor pharmacophore-based virtual screening approach. Eur J Pharm Sci 2020; 155:105537. [PMID: 32890663 PMCID: PMC7467125 DOI: 10.1016/j.ejps.2020.105537] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2020] [Revised: 08/10/2020] [Accepted: 08/30/2020] [Indexed: 12/30/2022]
Abstract
Chemokine receptors are key regulators of cell migration in terms of immunity and inflammation. Among these, CCR5 and CXCR4 play pivotal roles in cancer metastasis and HIV-1 transmission and infection. They act as essential co-receptors for HIV and furnish a route to the cell entry. In particular, inhibition of either CCR5 or CXCR4 leads very often the virus to shift to a more virulent dual-tropic strain. Therefore, dual receptor inhibition might improve the therapeutic strategies against HIV. In this study, we aimed to discover selective CCR5, CXCR4, and dual CCR5/CXCR4 antagonists using both receptor- and ligand-based computational methods. We employed this approach to fully incorporate the interaction attributes of the binding pocket together with molecular dynamics (MD) simulations and binding free energy calculations. The best hits were evaluated for their anti-HIV-1 activity against CXCR4- and CCR5-specific NL4.3 and BaL strains. Moreover, the Ca2+ mobilization assay was used to evaluate their antagonistic activity. From the 27 tested compounds, three were identified as inhibitors: compounds 27 (CCR5), 6 (CXCR4) and 3 (dual) with IC50 values ranging from 10.64 to 64.56 μM. The binding mode analysis suggests that the active compounds form a salt bridge with the glutamates and π-stacking interactions with the aromatic side chains binding site residues of the respective co-receptor. The presented hierarchical virtual screening approach provides essential aspects in identifying potential antagonists in terms of selectivity against a specific co-receptor. The compounds having multiple heterocyclic nitrogen atoms proved to be relatively more specific towards CXCR4 inhibition as compared to CCR5. The identified compounds serve as a starting point for further development of HIV entry inhibitors through synthesis and quantitative structure-activity relationship studies.
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Affiliation(s)
- Muhammad Usman Mirza
- Medicinal Chemistry, Department of Pharmaceutical and Pharmacological Sciences, Rega Institute for Medical Research, KU Leuven, B-3000 Leuven, Belgium
| | - Atefeh Saadabadi
- Pharmaceutical Sciences Laboratory, Faculty of Science and Engineering, Pharmacy, Åbo Akademi University, FI-20520 Turku, Finland; Structural Bioinformatics Laboratory, Faculty of Science and Engineering, Biochemistry, Åbo Akademi University, FI-20520 Turku, Finland
| | - Michiel Vanmeert
- Medicinal Chemistry, Department of Pharmaceutical and Pharmacological Sciences, Rega Institute for Medical Research, KU Leuven, B-3000 Leuven, Belgium
| | - Outi M H Salo-Ahen
- Pharmaceutical Sciences Laboratory, Faculty of Science and Engineering, Pharmacy, Åbo Akademi University, FI-20520 Turku, Finland; Structural Bioinformatics Laboratory, Faculty of Science and Engineering, Biochemistry, Åbo Akademi University, FI-20520 Turku, Finland
| | - Iskandar Abdullah
- Department of Chemistry, Faculty of Sciences, University Malaya, Kuala Lumpur 59100, Malaysia
| | - Sandra Claes
- Laboratory of Virology and Chemotherapy, Department of Microbiology, Immunology and Transplantation, Rega Institute for Medical Research, KU Leuven, B-3000 Leuven, Belgium
| | - Steven De Jonghe
- Laboratory of Virology and Chemotherapy, Department of Microbiology, Immunology and Transplantation, Rega Institute for Medical Research, KU Leuven, B-3000 Leuven, Belgium
| | - Dominique Schols
- Laboratory of Virology and Chemotherapy, Department of Microbiology, Immunology and Transplantation, Rega Institute for Medical Research, KU Leuven, B-3000 Leuven, Belgium
| | - Sarfraz Ahmad
- Department of Chemistry, Faculty of Sciences, University Malaya, Kuala Lumpur 59100, Malaysia
| | - Matheus Froeyen
- Medicinal Chemistry, Department of Pharmaceutical and Pharmacological Sciences, Rega Institute for Medical Research, KU Leuven, B-3000 Leuven, Belgium.
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6
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CCR5/CXCR4 Dual Antagonism for the Improvement of HIV Infection Therapy. Molecules 2019; 24:molecules24030550. [PMID: 30717348 PMCID: PMC6384722 DOI: 10.3390/molecules24030550] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2019] [Revised: 01/30/2019] [Accepted: 02/01/2019] [Indexed: 11/23/2022] Open
Abstract
HIV entry in the host cell requires the interaction with the CD4 membrane receptor, and depends on the activation of one or both co-receptors CCR5 and CXCR4. Former selective co-receptor antagonists, acting at early stages of infection, are able to impair the receptor functions, preventing the viral spread toward AIDS. Due to the capability of HIV to develop resistance by switching from CCR5 to CXCR4, dual co-receptor antagonists could represent the next generation of AIDS prophylaxis drugs. We herein present a survey on relevant results published in the last few years on compounds acting simultaneously on both co-receptors, potentially useful as preventing agents or in combination with classical anti-retroviral drugs based therapy.
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7
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Rashad AA, Song LR, Holmes AP, Acharya K, Zhang S, Wang ZL, Gary E, Xie X, Pirrone V, Kutzler MA, Long YQ, Chaiken I. Bifunctional Chimera That Coordinately Targets Human Immunodeficiency Virus 1 Envelope gp120 and the Host-Cell CCR5 Coreceptor at the Virus-Cell Interface. J Med Chem 2018; 61:5020-5033. [PMID: 29767965 DOI: 10.1021/acs.jmedchem.8b00477] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
To address the urgent need for new agents to reduce the global occurrence and spread of AIDS, we investigated the underlying hypothesis that antagonists of the HIV-1 envelope (Env) gp120 protein and the host-cell coreceptor (CoR) protein can be covalently joined into bifunctional synergistic combinations with improved antiviral capabilities. A synthetic protocol was established to covalently combine a CCR5 small-molecule antagonist and a gp120 peptide triazole antagonist to form the bifunctional chimera. Importantly, the chimeric inhibitor preserved the specific targeting properties of the two separate chimera components and, at the same time, exhibited low to subnanomolar potencies in inhibiting cell infection by different pseudoviruses, which were substantially greater than those of a noncovalent mixture of the individual components. The results demonstrate that targeting the virus-cell interface with a single molecule can result in improved potencies and also the introduction of new phenotypes to the chimeric inhibitor, such as the irreversible inactivation of HIV-1.
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Affiliation(s)
| | - Li-Rui Song
- CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica , Chinese Academy of Science , Shanghai 201203 , China.,College of Pharmaceutical Sciences , Soochow University Medical College , Suzhou 215123 , China.,University of Chinese Academy of Sciences , Number 19A Yuquan Road , Beijing 100049 , China
| | | | | | - Shiyu Zhang
- School of Biomedical Engineering, Science and Health Systems , Drexel University , Philadelphia , Pennsylvania 19104 , United States
| | - Zhi-Long Wang
- CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica , Chinese Academy of Science , Shanghai 201203 , China
| | | | - Xin Xie
- CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica , Chinese Academy of Science , Shanghai 201203 , China
| | | | | | - Ya-Qiu Long
- CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica , Chinese Academy of Science , Shanghai 201203 , China.,College of Pharmaceutical Sciences , Soochow University Medical College , Suzhou 215123 , China
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8
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Bailey LD, Kalyana Sundaram RV, Li H, Duffy C, Aneja R, Rosemary Bastian A, Holmes AP, Kamanna K, Rashad AA, Chaiken I. Disulfide Sensitivity in the Env Protein Underlies Lytic Inactivation of HIV-1 by Peptide Triazole Thiols. ACS Chem Biol 2015; 10:2861-73. [PMID: 26458166 DOI: 10.1021/acschembio.5b00381] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We investigated the mode of action underlying lytic inactivation of HIV-1 virions by peptide triazole thiol (PTT), in particular the relationship between gp120 disulfides and the C-terminal cysteine-SH required for virolysis. Obligate PTT dimer obtained by PTT SH cross-linking and PTTs with serially truncated linkers between pharmacophore isoleucine-ferrocenyltriazole-proline-tryptophan and cysteine-SH were synthesized. PTT variants showed loss of lytic activity but not binding and infection inhibition upon SH blockade. A disproportionate loss of lysis activity vs binding and infection inhibition was observed upon linker truncation. Molecular docking of PTT onto gp120 argued that, with sufficient linker length, the peptide SH could approach and disrupt several alternative gp120 disulfides. Inhibition of lysis by gp120 mAb 2G12, which binds at the base of the V3 loop, as well as disulfide mutational effects, argued that PTT-induced disruption of the gp120 disulfide cluster at the base of the V3 loop is an important step in lytic inactivation of HIV-1. Further, PTT-induced lysis was enhanced after treating virus with reducing agents dithiothreitol and tris (2-carboxyethyl)phosphine. Overall, the results are consistent with the view that the binding of PTT positions the peptide SH group to interfere with conserved disulfides clustered proximal to the CD4 binding site in gp120, leading to disulfide exchange in gp120 and possibly gp41, rearrangement of the Env spike, and ultimately disruption of the viral membrane. The dependence of lysis activity on thiol-disulfide interaction may be related to intrinsic disulfide exchange susceptibility in gp120 that has been reported previously to play a role in HIV-1 cell infection.
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Affiliation(s)
- Lauren D. Bailey
- Department
of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Ramalingam Venkat Kalyana Sundaram
- Department
of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
- School
of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, Pennsylvania 19104, United States
| | - Huiyuan Li
- Department
of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Caitlin Duffy
- Department
of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Rachna Aneja
- Department
of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | | | - Andrew P. Holmes
- Department
of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Kantharaju Kamanna
- Department
of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Adel A. Rashad
- Department
of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Irwin Chaiken
- Department
of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
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9
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Aneja R, Rashad AA, Li H, Kalyana Sundaram RV, Duffy C, Bailey LD, Chaiken I. Peptide Triazole Inactivators of HIV-1 Utilize a Conserved Two-Cavity Binding Site at the Junction of the Inner and Outer Domains of Env gp120. J Med Chem 2015; 58:3843-58. [PMID: 25860784 DOI: 10.1021/acs.jmedchem.5b00073] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
We used coordinated mutagenesis, synthetic design, and flexible docking to investigate the structural mechanism of Env gp120 encounter by peptide triazole (PT) inactivators of HIV-1. Prior results demonstrated that the PT class of inhibitors suppresses binding at both CD4 and coreceptor sites on Env and triggers gp120 shedding, leading to cell-independent irreversible virus inactivation. Despite these enticing anti-HIV-1 phenotypes, structural understanding of the PT-gp120 binding mechanism has been incomplete. Here we found that PT engages two inhibitor ring moieties at the junction between the inner and outer domains of the gp120 protein. The results demonstrate how combined occupancy of two gp120 cavities can coordinately suppress both receptor and coreceptor binding and conformationally entrap the protein in a destabilized state. The two-cavity model has common features with small molecule gp120 inhibitor binding sites and provides a guide for further design of peptidomimetic HIV-1 inactivators based on the PT pharmacophore.
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Affiliation(s)
- Rachna Aneja
- †Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Adel A Rashad
- †Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Huiyuan Li
- †Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Ramalingam Venkat Kalyana Sundaram
- †Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States.,‡School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, Pennsylvania 19104, United States
| | - Caitlin Duffy
- †Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Lauren D Bailey
- †Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Irwin Chaiken
- †Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
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10
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Rosemary Bastian A, Nangarlia A, Bailey LD, Holmes A, Kalyana Sundaram RV, Ang C, Moreira DRM, Freedman K, Duffy C, Contarino M, Abrams C, Root M, Chaiken I. Mechanism of multivalent nanoparticle encounter with HIV-1 for potency enhancement of peptide triazole virus inactivation. J Biol Chem 2014; 290:529-43. [PMID: 25371202 DOI: 10.1074/jbc.m114.608315] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Entry of HIV-1 into host cells remains a compelling yet elusive target for developing agents to prevent infection. A peptide triazole (PT) class of entry inhibitor has previously been shown to bind to HIV-1 gp120, suppress interactions of the Env protein at host cell receptor binding sites, inhibit cell infection, and cause envelope spike protein breakdown, including gp120 shedding and, for some variants, virus membrane lysis. We found that gold nanoparticle-conjugated forms of peptide triazoles (AuNP-PT) exhibit substantially more potent antiviral effects against HIV-1 than corresponding peptide triazoles alone. Here, we sought to reveal the mechanism of potency enhancement underlying nanoparticle conjugate function. We found that altering the physical properties of the nanoparticle conjugate, by increasing the AuNP diameter and/or the density of PT conjugated on the AuNP surface, enhanced potency of infection inhibition to impressive picomolar levels. Further, compared with unconjugated PT, AuNP-PT was less susceptible to reduction of antiviral potency when the density of PT-competent Env spikes on the virus was reduced by incorporating a peptide-resistant mutant gp120. We conclude that potency enhancement of virolytic activity and corresponding irreversible HIV-1 inactivation of PTs upon AuNP conjugation derives from multivalent contact between the nanoconjugates and metastable Env spikes on the HIV-1 virus. The findings reveal that multispike engagement can exploit the metastability built into virus the envelope to irreversibly inactivate HIV-1 and provide a conceptual platform to design nanoparticle-based antiviral agents for HIV-1 specifically and putatively for metastable enveloped viruses generally.
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Affiliation(s)
- Arangassery Rosemary Bastian
- From the Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, the School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, Pennsylvania 19104
| | - Aakansha Nangarlia
- From the Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, the School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, Pennsylvania 19104
| | - Lauren D Bailey
- From the Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102
| | - Andrew Holmes
- From the Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102
| | - R Venkat Kalyana Sundaram
- From the Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, the School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, Pennsylvania 19104
| | - Charles Ang
- From the Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, the School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, Pennsylvania 19104
| | - Diogo R M Moreira
- the Fundação Oswaldo Cruz, Centro de Pesquisas Goncalo Moniz, Salvador-BA 40296-710, Brazil
| | - Kevin Freedman
- the Department of Chemical and Biological Engineering, Drexel University, Philadelphia, Pennsylvania 19104, and
| | - Caitlin Duffy
- From the Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102
| | - Mark Contarino
- From the Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102
| | - Cameron Abrams
- the Department of Chemical and Biological Engineering, Drexel University, Philadelphia, Pennsylvania 19104, and
| | - Michael Root
- the Department of Biochemistry and Molecular Biology, Jefferson University, Philadelphia, Pennsylvania 19107
| | - Irwin Chaiken
- From the Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102,
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11
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Emileh A, Duffy C, Holmes AP, Rosemary Bastian A, Aneja R, Tuzer F, Rajagopal S, Li H, Abrams CF, Chaiken IM. Covalent conjugation of a peptide triazole to HIV-1 gp120 enables intramolecular binding site occupancy. Biochemistry 2014; 53:3403-14. [PMID: 24801282 PMCID: PMC4045323 DOI: 10.1021/bi500136f] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
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The HIV-1 gp120 glycoprotein is the
main viral surface protein
responsible for initiation of the entry process and, as such, can
be targeted for the development of entry inhibitors. We previously
identified a class of broadly active peptide triazole (PT) dual antagonists
that inhibit gp120 interactions at both its target receptor and coreceptor
binding sites, induce shedding of gp120 from virus particles prior
to host–cell encounter, and consequently can prevent viral
entry and infection. However, our understanding of the conformational
alterations in gp120 by which PT elicits its dual receptor antagonism
and virus inactivation functions is limited. Here, we used a recently
developed computational model of the PT–gp120 complex as a
blueprint to design a covalently conjugated PT–gp120 recombinant
protein. Initially, a single-cysteine gp120 mutant, E275CYU-2, was expressed and characterized. This variant retains excellent
binding affinity for peptide triazoles, for sCD4 and other CD4 binding
site (CD4bs) ligands, and for a CD4-induced (CD4i) ligand that binds
the coreceptor recognition site. In parallel, we synthesized a PEGylated
and biotinylated peptide triazole variant that retained gp120 binding
activity. An N-terminally maleimido variant of this PEGylated PT,
denoted AE21, was conjugated to E275C gp120 to produce the AE21–E275C
covalent conjugate. Surface plasmon resonance interaction analysis
revealed that the PT–gp120 conjugate exhibited suppressed binding
of sCD4 and 17b to gp120, signatures of a PT-bound state of envelope
protein. Similar to the noncovalent PT–gp120 complex, the covalent
conjugate was able to bind the conformationally dependent mAb 2G12.
The results argue that the PT–gp120 conjugate is structurally
organized, with an intramolecular interaction between the PT and gp120
domains, and that this structured state embodies a conformationally
entrapped gp120 with an altered bridging sheet but intact 2G12 epitope.
The similarities of the PT–gp120 conjugate to the noncovalent
PT–gp120 complex support the orientation of binding of PT to
gp120 predicted in the molecular dynamics simulation model of the
PT–gp120 noncovalent complex. The conformationally stabilized
covalent conjugate can be used to expand the structural definition
of the PT-induced “off” state of gp120, for example,
by high-resolution structural analysis. Such structures could provide
a guide for improving the subsequent structure-based design of inhibitors
with the peptide triazole mode of action.
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Affiliation(s)
- Ali Emileh
- Chemical and Biological Engineering, Drexel University , Philadelphia, Pennsylvania 19104, United States
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12
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Kwon YD, LaLonde JM, Yang Y, Elban MA, Sugawara A, Courter JR, Jones DM, Smith AB, Debnath AK, Kwong PD. Crystal structures of HIV-1 gp120 envelope glycoprotein in complex with NBD analogues that target the CD4-binding site. PLoS One 2014; 9:e85940. [PMID: 24489681 PMCID: PMC3904841 DOI: 10.1371/journal.pone.0085940] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2013] [Accepted: 12/05/2013] [Indexed: 11/19/2022] Open
Abstract
Efforts to develop therapeutic agents that inhibit HIV-1 entry have led to the identification of several small molecule leads. One of the most promising is the NBD series, which binds within a conserved gp120 cavity and possesses para-halogen substituted aromatic rings, a central oxalamide linker, and a tetramethylpiperidine moiety. In this study, we characterized structurally the interactions of four NBD analogues containing meta-fluoro substitution on the aromatic ring and various heterocyclic ring replacements of the tetramethylpiperidine group. The addition of a meta-fluorine to the aromatic ring improved surface complementarity and did not alter the position of the analogue relative to gp120. By contrast, heterocyclic ring replacements of the tetramethylpiperidine moiety exhibited diverse positioning and interactions with the vestibule of the gp120 cavity. Overall, the biological profile of NBD-congeners was modulated by ligand interactions with the gp120-cavity vestibule. Herein, six co-crystal structures of NBD-analogues with gp120 provide a structural framework for continued small molecule-entry inhibitor optimization.
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Affiliation(s)
- Young Do Kwon
- Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Judith M. LaLonde
- Department of Chemistry, Bryn Mawr College, Bryn Mawr, Pennsylvania, United States of America
| | - Yongping Yang
- Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Mark A. Elban
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Akihiro Sugawara
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Joel R. Courter
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - David M. Jones
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Amos B. Smith
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Asim K. Debnath
- Laboratory of Molecular Modeling and Drug Design, Lindsey F. Kimball Research Institute of the New York Blood Center, New York, New York, United States of America
| | - Peter D. Kwong
- Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
- * E-mail:
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13
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Bastian AR, Contarino M, Bailey LD, Aneja R, Moreira DRM, Freedman K, McFadden K, Duffy C, Emileh A, Leslie G, Jacobson JM, Hoxie JA, Chaiken I. Interactions of peptide triazole thiols with Env gp120 induce irreversible breakdown and inactivation of HIV-1 virions. Retrovirology 2013; 10:153. [PMID: 24330857 PMCID: PMC3878761 DOI: 10.1186/1742-4690-10-153] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2013] [Accepted: 12/02/2013] [Indexed: 11/10/2022] Open
Abstract
Background We examined the underlying mechanism of action of the peptide triazole thiol, KR13 that has been shown previously to specifically bind gp120, block cell receptor site interactions and potently inhibit HIV-1 infectivity. Results KR13, the sulfhydryl blocked KR13b and its parent non-sulfhydryl peptide triazole, HNG156, induced gp120 shedding but only KR13 induced p24 capsid protein release. The resulting virion post virolysis had an altered morphology, contained no gp120, but retained gp41 that bound to neutralizing gp41 antibodies. Remarkably, HIV-1 p24 release by KR13 was inhibited by enfuvirtide, which blocks formation of the gp41 6-helix bundle during membrane fusion, while no inhibition of p24 release occurred for enfuvirtide-resistant virus. KR13 thus appears to induce structural changes in gp41 normally associated with membrane fusion and cell entry. The HIV-1 p24 release induced by KR13 was observed in several clades of HIV-1 as well as in fully infectious HIV-1 virions. Conclusions The antiviral activity of KR13 and its ability to inactivate virions prior to target cell engagement suggest that peptide triazole thiols could be highly effective in inhibiting HIV transmission across mucosal barriers and provide a novel probe to understand biochemical signals within envelope that are involved in membrane fusion.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | | | | | | | - Irwin Chaiken
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, 245N 15th Street, New College Building, Room No, 11102, Philadelphia, PA 19102, USA.
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14
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Emileh A, Tuzer F, Yeh H, Umashankara M, Moreira DRM, Lalonde JM, Bewley CA, Abrams CF, Chaiken IM. A model of peptide triazole entry inhibitor binding to HIV-1 gp120 and the mechanism of bridging sheet disruption. Biochemistry 2013; 52:2245-61. [PMID: 23470147 DOI: 10.1021/bi400166b] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Peptide triazole (PT) entry inhibitors prevent HIV-1 infection by blocking the binding of viral gp120 to both the HIV-1 receptor and the coreceptor on target cells. Here, we used all-atom explicit solvent molecular dynamics (MD) to propose a model for the encounter complex of the peptide triazoles with gp120. Saturation transfer difference nuclear magnetic resonance (STD NMR) and single-site mutagenesis experiments were performed to test the simulation results. We found that docking of the peptide to a conserved patch of residues lining the "F43 pocket" of gp120 in a bridging sheet naïve gp120 conformation of the glycoprotein led to a stable complex. This pose prevents formation of the bridging sheet minidomain, which is required for receptor-coreceptor binding, providing a mechanistic basis for dual-site antagonism of this class of inhibitors. Burial of the peptide triazole at the gp120 inner domain-outer domain interface significantly contributed to complex stability and rationalizes the significant contribution of hydrophobic triazole groups to peptide potency. Both the simulation model and STD NMR experiments suggest that the I-X-W [where X is (2S,4S)-4-(4-phenyl-1H-1,2,3-triazol-1-yl)pyrrolidine] tripartite hydrophobic motif in the peptide is the major contributor of contacts at the gp120-PT interface. Because the model predicts that the peptide Trp side chain hydrogen bonding with gp120 S375 contributes to the stability of the PT-gp120 complex, we tested this prediction through analysis of peptide binding to gp120 mutant S375A. The results showed that a peptide triazole KR21 inhibits S375A with 20-fold less potency than WT, consistent with predictions of the model. Overall, the PT-gp120 model provides a starting point for both the rational design of higher-affinity peptide triazoles and the development of structure-minimized entry inhibitors that can trap gp120 into an inactive conformation and prevent infection.
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Affiliation(s)
- Ali Emileh
- Chemical and Biological Engineering, Drexel University, Philadelphia, PA 19104, USA.
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15
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Kamanna K, Aneja R, Duffy C, Kubinski P, Moreira DR, Bailey LD, McFadden K, Schön A, Holmes A, Tuzer F, Contarino M, Freire E, Chaiken IM. Non-natural peptide triazole antagonists of HIV-1 envelope gp120. ChemMedChem 2013; 8:322-8. [PMID: 23239505 PMCID: PMC3810028 DOI: 10.1002/cmdc.201200422] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2012] [Revised: 11/08/2012] [Indexed: 11/06/2022]
Abstract
We investigated the derivation of non-natural peptide triazole dual receptor site antagonists of HIV-1 Env gp120 to establish a pathway for developing peptidomimetic antiviral agents. Previously we found that the peptide triazole HNG-156 [R-I-N-N-I-X-W-S-E-A-M-M-CONH(2), in which X=ferrocenyltriazole-Pro (FtP)] has nanomolar binding affinity to gp120, inhibits gp120 binding to CD4 and the co-receptor surrogate mAb 17b, and has potent antiviral activity in cell infection assays. Furthermore, truncated variants of HNG-156, typified by UM-24 (Cit-N-N-I-X-W-S-CONH(2)) and containing the critical central stereospecific (L)X-(L)W cluster, retain the functional characteristics of the parent peptide triazole. In the current work, we examined the possibility of replacing natural with unnatural residue components in UM-24 to the greatest extent possible. The analogue with the critical "hot spot" residue Trp 6 replaced with L-3-benzothienylalanine (Bta) (KR-41), as well as a completely non-natural analogue containing D-amino acid substitutions outside the central cluster (KR-42, (D)Cit-(D)N-(D)N-(D)I-X-Bta-(D)S-CONH(2)), retained the dual receptor site antagonism/antiviral activity signature. The results define differential functional roles of subdomains within the peptide triazole and provide a structural basis for the design of metabolically stable peptidomimetic inhibitors of HIV-1 Env gp120.
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Affiliation(s)
- Kantharaju Kamanna
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, 245N, 15 Street, New College Building, Room 11302, Philadelphia, PA, 19102 (USA)
| | - Rachna Aneja
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, 245N, 15 Street, New College Building, Room 11302, Philadelphia, PA, 19102 (USA)
| | - Caitlin Duffy
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, 245N, 15 Street, New College Building, Room 11302, Philadelphia, PA, 19102 (USA)
| | - Pamela Kubinski
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, 245N, 15 Street, New College Building, Room 11302, Philadelphia, PA, 19102 (USA)
| | - Diogo Rodrigo Moreira
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, 245N, 15 Street, New College Building, Room 11302, Philadelphia, PA, 19102 (USA)
| | - Lauren D Bailey
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, 245N, 15 Street, New College Building, Room 11302, Philadelphia, PA, 19102 (USA)
| | - Karyn McFadden
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, 245N, 15 Street, New College Building, Room 11302, Philadelphia, PA, 19102 (USA)
| | - Arne Schön
- Department of Biology, The Johns Hopkins University, Baltimore, Maryland 21218 (USA)
| | - Andrew Holmes
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, 245N, 15 Street, New College Building, Room 11302, Philadelphia, PA, 19102 (USA)
| | - Ferit Tuzer
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, 245N, 15 Street, New College Building, Room 11302, Philadelphia, PA, 19102 (USA)
| | - Mark Contarino
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, 245N, 15 Street, New College Building, Room 11302, Philadelphia, PA, 19102 (USA)
| | - Ernesto Freire
- Department of Biology, The Johns Hopkins University, Baltimore, Maryland 21218 (USA)
| | - Irwin M Chaiken
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, 245N, 15 Street, New College Building, Room 11302, Philadelphia, PA, 19102 (USA)
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