Abstract
The HIV-1 envelope (Env) is an essential determinant of viral infectivity, tropism and spread between T cells. Lentiviral Env contain an unusually long 150 amino acid cytoplasmic tail (EnvCT), but the function of the EnvCT and many conserved domains within it remain largely uncharacterised. Here, we identified a highly conserved tryptophan motif at position 757 (W757) in the LLP-2 alpha helix of the EnvCT as a key determinant for HIV-1 replication and spread between T cells. Alanine substitution at this position potently inhibited HIV-1 cell–cell spread (the dominant mode of HIV-1 dissemination) by preventing recruitment of Env and Gag to sites of cell–cell contact, inhibiting virological synapse (VS) formation and spreading infection. Single-molecule tracking and super-resolution imaging showed that mutation of W757 dysregulates Env diffusion in the plasma membrane and increases Env mobility. Further analysis of Env function revealed that W757 is also required for Env fusion and infectivity, which together with reduced VS formation, result in a potent defect in viral spread. Notably, W757 lies within a region of the EnvCT recently shown to act as a supporting baseplate for Env. Our data support a model in which W757 plays a key role in regulating Env biology, modulating its temporal and spatial recruitment to virus assembly sites and regulating the inherent fusogenicity of the Env ectodomain, thereby supporting efficient HIV-1 replication and spread.
Highlights
Virus assembly is a well-orchestrated event in which all components must be temporally and spatially recruited to the right place at the right time to regulate successfully infectious viral egress and spreading infection
To identify novel determinants in EnvCT that play a role in human immunodeficiency virus type-1 (HIV-1) replication and spread, we focused on tryptophan (W) residues that possess a large, bulky hydrophobic side chain and act as key mediators of protein–protein and protein–lipid interactions, including within the W-rich HIV-1 MPER [42,43]
We focused on cell–cell spread, which is the dominant mode of HIV-1 dissemination between T cells and takes place at the virological synapse (VS)
Summary
Virus assembly is a well-orchestrated event in which all components must be temporally and spatially recruited to the right place at the right time to regulate successfully infectious viral egress and spreading infection. For the lentivirus human immunodeficiency virus type-1 (HIV-1), replication predominantly takes place in CD4+ T cells, with virus assembly and budding occurring at the plasma membrane (PM) [1]. HIV-1 has two major structural proteins: the envelope glycoprotein (Env) that engages CD4 and co-receptor (CCR5 or CXCR4) and mediates fusion of the viral lipid membrane and the target cell plasma membrane to mediate entry, as well as the Gag p55 polyprotein that undergoes cleavage by the viral protease during budding, a step that is required for viral maturation and infectivity, producing the Gag components capsid, matrix, nucleocapsid, and p6. Recent super-resolution imaging has shown that the Gag lattice forms early during the course of viral assembly, with
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