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

Researchers investigated the molecular mechanisms by which P-selectin glycoprotein ligand-1 (PSGL-1) restricts HIV-1. Previous work established that PSGL-1 is incorporated into virions and limits viral infectivity, but the specific process by which PSGL-1 prevents the inclusion of HIV-1 envelope protein (Env) into new virus particles remained poorly defined.

Using a combination of molecular biology and computational structural analysis, the researchers created a panel of PSGL-1 mutants with deletions in either their extracellular (EC) or intracellular (IC) domains. They systematically investigated the role of the extracellular decameric repeats (DRs) by deleting them in sequential segments. Finally, they utilized AlphaFold 3 to model the three-dimensional structure of these DRs to determine how the length of the repeat region affects the overall conformation of the protein.

The team demonstrated that both the EC and IC domains of PSGL-1 are necessary to effectively exclude Env from virions. Specifically, they found that a minimum of nine decameric repeats is required for this exclusionary function. Molecular modeling revealed that as the number of DRs increases beyond seven, the extracellular domain undergoes a dramatic structural transition—moving from an extended, rod-like structure to a collapsed, coil-like conformation. This change in shape significantly increases the physical footprint of the protein on the virion surface. The researchers proposed that this collapsed structure creates spatial competition at the site of virion assembly, effectively blocking the display or incorporation of Env.

This study provides a biophysical explanation for how a host glycoprotein can act as a restriction factor against HIV-1. By identifying the importance of the rod-to-coil structural transition of the DR region, the researchers have shed light on the mechanical aspects of viral inhibition. This knowledge enhances our understanding of the delicate molecular interplay between host restriction factors and viral assembly, providing new insights into the structural constraints of the HIV virion.