Nand, E. | bioRxiv Science

bioRxiv2024

The conserved HIV-1 spacer peptide 2 triggers matrix lattice maturation

HIV-1 particles are released in an immature, non-infectious form. Proteolytic cleavage of the main structural polyprotein Gag into functional domains induces rearrangement into mature, infectious virions. In immature virus particles, the Gag membrane binding domain, MA, forms a hexameric protein lattice that undergoes structural transition upon cleavage into a distinct, mature MA lattice. The mechanism of MA lattice maturation is unknown. Here we show that released spacer peptide 2 (SP2), a conserved peptide of unknown function situated [~]300 residues downstream of MA, binds MA to induce structural maturation. By high-resolution in-virus structure determination of MA, we show that MA does not bind lipid into a side pocket as previously thought, but instead binds SP2 as an integral part of the protein-protein interfaces that stabilise the mature lattice. Analysis of Gag cleavage site mutants showed that SP2 release is required for MA maturation, and we demonstrate that SP2 is sufficient to induce maturation of purified MA on lipid layers in vitro. SP2-triggered MA maturation correlated with faster fusion of virus with target cells. Our results reveal a new, unexpected interaction between two HIV-1 components, provide a high-resolution structure of mature MA, establish the trigger of MA structural maturation, and assign function to the SP2 peptide.

microbiology↗

bioRxiv2022

Asymmetric HIV-1 envelope trimers bound to one and two CD4 molecules are intermediates during membrane binding

Human immunodeficiency virus 1 (HIV-1) infection is initiated by binding of the viral envelope glycoprotein (Env) to the cell-surface receptor CD4. Although high resolution structures of Env complexed with soluble domains of CD4 have been determined, the binding process is less understood on native membranes. Here, we apply cryo-electron tomography (cryo-ET) to monitor Env-CD4 interactions at membrane-membrane interfaces formed between HIV-1 and CD4-presenting virus-like particles. Env-CD4 complexes organized into clusters and rings, bringing opposing membranes closer together. Additionally, Env-CD4 clustering was dependent on capsid maturation. Subtomogram averaging and classification revealed that Env bound one, two, and finally three CD4 molecules, upon which Env adopted a partially open state. Our data indicate that asymmetric HIV-1 Env trimers bound to one and two CD4 molecules are detectable intermediates during virus binding to host cell membranes, which likely has consequences for antibody-mediated immune responses and vaccine immunogen design.

microbiology↗