A Conserved Tryptophan-Rich Motif in the Membrane-Proximal Region of the Human Immunodeficiency Virus Type 1 gp41 Ectodomain Is Important for Env-Mediated Fusion and Virus Infectivity

摘要: The process of viral entry is a key step in the initiation human immunodeficiency virus type 1 (HIV-1) infection. Attachment HIV-1 virion to target cell mediated by binding envelope glycoprotein complex CD4 receptor on surface (reviewed reference 49). (Env) processed from an oligomeric precursor protein, gp160, into two noncovalently linked subunits: subunit, gp120, which responsible for CD4, and transmembrane gp41, initiates membrane fusion. In addition has also been shown require interaction between gp120 coreceptor, members family seven-transmembrane G protein-coupled chemokine receptors, order mediate fusion (18). Many viruses, such as influenza virus, are endocytosed following their (35). Their glycoproteins then undergo pH-activated conformational change fusion-competent form acidic environment endosome (13, 23). HIV, however, fuses directly with plasma at pH-independent manner (37, 38, 53). case it that induces changes increases exposure gp41 epitopes independent dissociation (48, 50, 51). Thus, proposed HIV undergoes receptor-induced activation analogous pH-induced other glycoproteins. The amino-terminal peptide was originally identified its similarity functional domains paramyxovirus (22) since extensively characterized through mutagenesis primary domain (3, 19, 52). Based analogy similar rearrangements (13) Rous sarcoma (24, 27), CD4-induced believed ultimately lead insertion membrane. details this how gp120-coreceptor contributes unclear. However, recent studies have suggested may be involved leading Mutagenesis heptad repeat, leucine zipper-like motif ectodomain demonstrated hydrophobicity position 573 center repeat dictated efficiency (9, 10, 16). It hypothesized, based (7, 55–60), forming coiled-coil structure oligomer, formed acid-activated fragment hemagglutinin (HA) (5), binding. While cytoplasmic tail not required (17, 21, 62, 63), we others event does contain membrane-spanning anchor, substitution covalently lipid anchor did support (46, 54). structural requirements domain, less clear. Truncation carboxy terminus beyond lysine residue 683 (HXB2 strain) sufficient cause loss anchoring secretion soluble 43), whereas truncation just after arginine 696 results stably anchored protein expressed (43), suggesting minimal could residues 684 695. Similar obtained simian (SIV) Env proteins where 691 707 incorporation virions (29). these truncated were nonfunctional, C terminal important function (43). These suggest while can forced use abbreviated completion reaction. The described here focus membrane-proximal region unusually rich tryptophan residues, several conserved both primate ungulate lentiviruses (Fig. ​(Fig.1A1A B). This overlaps biologically gp41. Two peptides, DP-178 SJ-2176, derived potently inhibit HIV-mediated (28, 61). A neutralizing monoclonal antibody, 2F5, whose epitope (40, 41). Interestingly, become inaccessible binding, conformation (51). FIG. 1 Sequence conservation predicted tryptophan-rich region. (A) Schematic representation showing location sequence variability overlapping sequences 2F5 ... In examine role glycoprotein, created deletion, substitution, mutations site-directed mutagenesis. Our analyses resulting mutant indicate stretch 17 hydrophobic uncharged amino acids immediately adjacent border dispensable normal maturation, transport, CD4-binding ability but Env-mediated contrast deletions multiple point abrogate fusion, even subtle had profound effect infectivity. Features discussed relation possible mechanism virus.