A conserved acidic cluster motif in SERINC5 confers resistance to antagonism by HIV-1 Nef

Abstract

The cellular protein SERINC5 inhibits the infectivity of diverse retroviruses and is counteracted by the glycoGag protein of MLV, the S2 protein of EIAV, and the Nef protein of HIV-1. Determining regions within SERINC5 that provide restrictive activity or Nef-sensitivity should inform mechanistic models of the SERINC5/HIV-1 relationship. Here, we report that deletion of the highly conserved sequence EDTEE, which is located within a cytoplasmic loop of SERINC5 and is reminiscent of an acidic cluster membrane trafficking signal, increases the sensitivity of SERINC5 to antagonism by Nef while having no effect on the intrinsic activity of the protein as an inhibitor of infectivity. The effects on infectivity correlated with enhanced removal of the {Delta}EDTEE mutant relative to wild type SERINC5 from the cell surface and with enhanced exclusion of the mutant protein from virions by Nef. Mutational analysis revealed that the acidic residues, but not the threonine, within the EDTEE motif are important for the relative resistance to Nef. Deletion of the EDTEE sequence did not increase the sensitivity of SERINC5 to antagonism by the glycoGag protein of MLV, suggesting that its virologic role is Nef-specific. These results are consistent with the reported mapping of the cytoplasmic loop that contains the EDTEE sequence as a general determinant of Nef-responsiveness, but they further indicate that sequences inhibitory to as well as supportive of Nef-activity reside in this region. We speculate that the EDTEE motif might have evolved to mediate resistance against retroviruses that use Nef-like proteins to antagonize SERINC5.\n\nImportanceCellular membrane proteins in the SERINC family, especially SERINC5, inhibit the infectivity of retroviral virions. This inhibition is counteracted by retroviral proteins, specifically HIV-1 Nef, MLV glycoGag, and EIAV S2. One consequence of such a host-pathogen \"arms race\" is compensatory change in the host antiviral protein as it evolves to escape the effects of the viral antagonist. This is often reflected in a genetic signature, positive selection, which is conspicuously missing in SERINC5. Here we show that despite this lack of genetic evidence, a sequence in SERINC5 nonetheless provides relative resistance to antagonism by HIV-1 Nef.