title: Activation and Inactivation of Primary Human Immunodeficiency Virus Envelope Glycoprotein Trimers by CD4-Mimetic Compounds.
abstract: Human immunodeficiency virus type 1 (HIV-1) entry into cells is mediated by the viral envelope glycoproteins (Env), a trimer of three gp120 exterior glycoproteins, and three gp41 transmembrane glycoproteins. The metastable Env is triggered to undergo entry-related conformational changes when gp120 binds sequentially to the receptors, CD4 and CCR5, on the target cell. Small-molecule CD4-mimetic compounds (CD4mc) bind gp120 and act as competitive inhibitors of gp120-CD4 engagement. Some CD4mc have been shown to trigger Env prematurely, initially activating Env function, followed by rapid and irreversible inactivation. Here, we study CD4mc with a wide range of anti-HIV-1 potencies and demonstrate that all tested CD4mc are capable of activating as well as inactivating Env function. Biphasic dose-response curves indicated that the occupancy of the protomers in the Env trimer governs viral activation versus inactivation. One CD4mc bound per Env trimer activated HIV-1 infection. Envs with two CD4mc bound were activated for infection of CD4-negative, CCR5-positive cells, but the infection of CD4-positive, CCR5-positive cells was inhibited. Virus was inactivated when all three Env protomers were occupied by the CD4mc, and gp120 shedding from the Env trimer was increased in the presence of some CD4mc. Env reactivity and the on rates of CD4mc binding to the Env trimer were found to be important determinants of the potency of activation and entry inhibition. Cross-sensitization of Env protomers that do not bind the CD4mc to neutralization by an anti-V3 antibody was not evident. These insights into the mechanism of antiviral activity of CD4mc should assist efforts to optimize their potency and utility.
  
  
  OBJECTIVE
  The trimeric envelope glycoproteins of human immunodeficiency virus type 1 (HIV-1) mediate virus entry into host cells. Binding to the host cell receptors, CD4 and CCR5, triggers changes in the conformation of the HIV-1 envelope glycoprotein trimer important for virus entry. Small-molecule CD4-mimetic compounds inhibit HIV-1 infection by multiple mechanisms: (i) direct blockade of the interaction between the gp120 exterior envelope glycoprotein and CD4; (ii) premature triggering of conformational changes in the envelope glycoproteins, leading to irreversible inactivation; and (iii) exposure of cryptic epitopes to antibodies, allowing virus neutralization. The consequences of the binding of the CD4-mimetic compound to the HIV-1 envelope glycoproteins depends upon how many of the three subunits of the trimer are bound and upon the propensity of the envelope glycoproteins to undergo conformational changes. Understanding the mechanistic factors that influence the activity of CD4-mimetic compounds can help to improve their potency and coverage of diverse HIV-1 strains.
authors.affiliation: Department of Cancer Immunology and Virology, Dana-Farber Cancer Institute, Boston, Massachusetts, USA.|Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Navid
authors.initials: N
authors.lastname: Madani
authors.affiliation: Department of Cancer Immunology and Virology, Dana-Farber Cancer Institute, Boston, Massachusetts, USA.
authors.forename: Amy M
authors.initials: AM
authors.lastname: Princiotto
authors.affiliation: Department of Cancer Immunology and Virology, Dana-Farber Cancer Institute, Boston, Massachusetts, USA.
authors.forename: Connie
authors.initials: C
authors.lastname: Zhao
authors.affiliation: Department of Cancer Immunology and Virology, Dana-Farber Cancer Institute, Boston, Massachusetts, USA.
authors.forename: Fatemeh
authors.initials: F
authors.lastname: Jahanbakhshsefidi
authors.affiliation: Department of Cancer Immunology and Virology, Dana-Farber Cancer Institute, Boston, Massachusetts, USA.
authors.forename: Max
authors.initials: M
authors.lastname: Mertens
authors.affiliation: Department of Cancer Immunology and Virology, Dana-Farber Cancer Institute, Boston, Massachusetts, USA.|Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Alon
authors.initials: A
authors.lastname: Herschhorn
authors.affiliation: Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Bruno
authors.initials: B
authors.lastname: Melillo
authors.affiliation: Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Amos B
authors.initials: AB
authors.lastname: Smith
authors.affiliation: Department of Cancer Immunology and Virology, Dana-Farber Cancer Institute, Boston, Massachusetts, USA joseph_sodroski@dfci.harvard.edu.|Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts, USA.|Department of Immunology and Infectious Diseases, Harvard T.H. Chan School of Public Health, Boston, Massachusetts, USA.
authors.forename: Joseph
authors.initials: J
authors.lastname: Sodroski
mesh_terms: D019380:Anti-HIV Agents / Q000737:chemistry / Q000494:pharmacology; D057134:Antibodies, Neutralizing / Q000494:pharmacology; D015704:CD4 Antigens / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D015726:Giant Cells; D015483:HIV Antibodies / Q000494:pharmacology; D015699:HIV Envelope Protein gp120 / Q000819:agonists / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics; D015658:HIV Infections / Q000235:genetics / Q000378:metabolism / Q000821:virology; D015497:HIV-1 / Q000187:drug effects / Q000502:physiology; D006801:Humans; D020128:Inhibitory Concentration 50; D008826:Microbial Sensitivity Tests; D018716:Molecular Mimicry; D009154:Mutation; D010641:Phenotype; D011485:Protein Binding; D055503:Protein Multimerization; D019713:Receptors, CCR5 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D053586:Virus Internalization
chemical_list: D019380:Anti-HIV Agents; D057134:Antibodies, Neutralizing; D015704:CD4 Antigens; D015483:HIV Antibodies; D015699:HIV Envelope Protein gp120; D019713:Receptors, CCR5
keywords: antibody; conformation; envelope glycoprotein; inhibitor; neutralization; sensitization; stoichiometry; virus entry