SERINC5(S5) is a multi-span transmembrane protein that potently blocks the infectivity of HIV-1 produced by human T-cells. The ability of S5 to restrict infectivity correlates with its presence in the virion, but the exact mechanism by which S5 restricts HIV-1 is unknown. Here we tested whether the core from HIV-1 virions containing S5 is delivered to the cytoplasm. Using the “fate of the capsid” assay, we demonstrated that the viral core of S5-restricted HIV-1 does not reach the cytoplasm of target cells, suggesting a block in the delivery of the core to the cytoplasm. In agreement with evidence suggesting that the viral determinants for S5 restriction map to the envelope of HIV-1, we observed that S5 induces conformational changes to the HIV-1 envelope. Further, we demonstrated that S5 localizes to detergent-resistant membranes (DRMs), as has been shown previously for the HIV-1 envelope in producer cells. In order to identify the determinants of S5 restriction, we explored the ability of all human SERINC proteins to restrict HIV-1. In contrast to human S5, we observed that human SERINC2(S2) did not restrict HIV-1, and was inefficiently incorporated into HIV-1 virions when compared to S5. Experiments using S5-S2 chimeric proteins revealed two functional domains for restriction: one necessary for S5 incorporation into virions, which does not seem to be necessary for restriction, and a second one necessary to change the HIV-1 envelope conformation, localize to DRMs, and block infection.
Bibliographical noteFunding Information:
We thank the NIH AIDS repository and other indicated donors for generously providing the following reagents: TAK-779, anti-HIV-1 gp41 monoclonal antibodies (4E10 and 2F5), anti-HIV-1 gp120, monoclonal antibody ( 2G12 ) from Polymun Scientific, monoclonal antibody (10E8) from Dr. Mark Connors, anti-HIV-1 gp120 monoclonal antibody (3BNC117) from Dr. Michel C. Nussenzweig, HIV-1 p24 monoclonal antibody (183-H12-5C) from Dr. Bruce Chesebro and Kathy Wehrly, anti-HIV-1 gp41 monoclonal antibody (NC-1) from Dr. Shibo Jiang, Anti-HIV-1 gp120 Monoclonal (PG9), Anti-HIV-1 gp120 Monoclonal (VRC01), from Dr. John Mascola, and anti-HIV-1 gp41 monoclonal antibody ( 240-D ) from Dr. Susan Zolla-Pazner. The work was supported by an R01 grant from the NIH ( AI087390 , to F.D.-G).