PSGL-1 excludes HIV Env from virion surface through spatial hindrance involving structural folding of the decameric repeats (DR)

P-selectin glycoprotein ligand-1 (PSGL-1), a mucin-like surface glycoprotein, is primarily expressed on lymphoid and myeloid cells.

PSGL-1 has recently been identified as an HIV restriction factor, blocking HIV infectivity mainly through virion incorporation that sterically hinders virion attachment to target cells.

PSGL-1 also inhibits HIV Env incorporation into virions.

However, the molecular mechanisms of PSGL-1-mediated Env exclusion remained unclear.

Here, we investigated the role of PSGL-1’s extracellular (EC) and intracellular (IC) domains in Env exclusion.

We demonstrate that both EC and IC are important for Env exclusion; when EC was deleted, PSGL-1 completely lost its ability to inhibit Env incorporation, whereas when IC was deleted, PSGL-1 partially lost this activity.

In addition, when the decameric repeats (DR) were deleted from EC, PSGL-1 also lost its ability to inhibit Env incorporation.

Sequential DR deletion mutagenesis further demonstrated that a minimum of 9 DRs is necessary for Env exclusion.

Molecular modeling of the DR structure revealed that PSGL-1 mutants with 7 or fewer DRs pose as an extended “rod-like” structure, whereas those with 9 or more DRs collapse into a “coil-like” structure that spatially excludes Env.

Our studies suggest a model in which Env exclusion involves Gag-mediated PSGL-1 targeting to the virion assembly site where DR-mediated spatial exclusion blocks Env incorporation.