Role of gRNA binding in HIV-1 Gag assembly process.

Abstract

Assembly of human immunodeficiency virus type 1 (HIV-1) is a multi-step process that occurs at the host cell plasma membrane and is driven by a viral structural protein, Gag. Newly synthesized cytosolic Gag particles are targeted to the inner leaflet of the plasma membrane and membrane-bound Gag polyproteins interact with each other to form higher order multimers. Gag polyprotein is composed of multiple structured domains connected by flexible linkers. N-myristoylated matrix (MA) domain mediates membrane binding process, capsid (CA) and nucleocapsid (NC) domains play vital roles in Gag multimerization process. Interactions of gRNA with the zinc finger motifs of the NC domain facilitate gRNA packaging into virions. To investigate the effect of Gag-gRNA binding on the different multimerization states, we have performed all-atom molecular dynamics simulations of full-length Gag multimers (hexamer and hexamer-of-trimers) bound to an asymmetric membrane. MA domain multimerizes as a hexamer of trimers whereas cryo-ET data shows that CA domains are organized as hexameric lattice. The multidomain correlation of Gag polyprotein as well as the effect of multimerization of one domain to the dynamics of others are still not clear. Here we aim to gain atomic-level characterization of the inter and intra-protein interactions between different structural domains of Gag polyprotein in the presence/absence of the effective rigidity of NC domain, associated with gRNA binding. In the hexamer-of-trimers, the rigidity of NC domain is observed to modify the structure and dynamics of Gag monomers, resulting in a different binding surface for cytosolic Gag protein. In case of membrane-bound Gag hexamer, gRNA binding alters the dynamics of MA-CA linker domains, and we observe a signature of PIP2 and cholesterol enrichment in the membrane that can modify membrane binding affinity for Gag hexamer and facilitate recruitment of cytosolic Gag protein.