Molecular Modeling of the DR domain of an HIV restriction factor PSGL-1 - Project Summary/Abstract Studying the anti-HIV mechanisms of restriction factors is central to understanding virus-host interaction and for developing novel therapeutics. Recently, PI Wu's lab has co-identified a new HIV restriction factor, PSGL-1 (P-selectin glycoprotein ligand-1), that inactivates the infectivity of HIV virions released from HIV producing cells. Wu and his collaborators have further demonstrated that PSGL-1 acts through a novel mechanism of virion incorporation of PSGL-1 that sterically hinders particle attachment to target cells. PSGL-1 is a dimeric mucin-like 120-KD glycoprotein that is primarily expressed on the surface of lymphoid and myeloid cells, and binds to P-, L-, and E-selectins for leukocyte rolling and transmigration. Structurally, PSGL-1 has a relatively rigid and elongated extracellular domain that extends nearly 60 nm from cell surface. A large structural part of the extracellular domain also consists of 14-16 tandem decameric repeats (DR), which are characterized by repeated stretches of 10 amino acids with numerous O-glycosylated threonines (30%) and prolines (10%). Our preliminary studies discovered that DR plays a pivotal role in PSGL-1's anti-HIV activity, and a single DR possesses basic anti-viral activity. Nevertheless, individual DR shows amino acid sequence variation and varying degrees of anti-viral activity. We hypothesize that the structural rigidity and glycosylation of DR affect its anti-HIV activity. The proposed research integrates molecular dynamics simulations, machine learning, and laboratory experiments to study the anti-HIV properties of DR. The proposal has two aims. Aim 1 is to determine the structure-function relationship of DR via the integration of In silico molecular modeling, DNA mutagenesis, and functional anti-HIV assays. We will apply all-atom replica exchange with solute tempering (REST) molecular dynamics simulations to examine DR glycosylation, rigidity, and extension. We will also apply machine learning to feature datasets extracted from molecular simulation of DR variants. We expect that the integration of our studies from molecular modeling, DR mutagenesis, and functional anti-HIV assays will guide the design of novel PSGL-1 variants with greater anti-HIV activity. Aim 2 is to test and validate the anti-HIV activity of PSGL-1 in vivo in a humanized mouse model for control of HIV replication in the absence of ART. The proposed work will identify how DR residue positioning and composition quantitatively correlate with PSGL-1's anti-HIV function. Our study will also help developing novel therapeutics, based on PSGL-1's anti-HIV activity, for a functional cure of HIV infection.
