Cooperativity in the Interactions of HIV-1 Gag Protein with Short Nucleic Acid

Authors

• H ZHAO
• S DATTA
• S KIM
• S CHATURVEDI
• A REIN
• P SCHUCK

Abstract

The assembly of HIV-1 viral particles is driven by self-association of the polyprotein Gag and controlled by interactions with the host membrane and with viral RNA. Many essential aspects of the molecular mechanism leading to assembly are known, however, the process is not yet fully understood particularly the interrelationship of the interactions. HIV-1 Gag is a polyprotein with individually folded domains (among others) for membrane interactions (MA), capsid interactions (CA) and nucleic acid binding (NC), linked by intrinsically unstructured regions. Multi-valent and mutually competitive binding of MA and NC to nucleic acid causes global and local structural rearrangements of domains and linkers that generate strong cooperativity in the CA-mediated self-assembly. While particle assembly can be readily observed in vitro after addition of nucleic acid to recombinant Gag, the coordinated initial steps is challenging to investigate by biophysical analysis. During the last decades, our laboratory has developed new sedimentation velocity analytical ultracentrifugation (SV-AUC) tools for studying energetics of complex homo- and hetero-associations of proteins, with high mass-dependent resolution of co-existing assembly states in solution, and with sub-nanomolar detection sensitivity based on fluorescence. Through applications of fluorescence detection in SV-AUC, we discovered new aspects of the interactions of Gag with nucleic acids and lipids that promote assembly. This is supported in our experiments of wild-type Gag and CA-mutants binding to fluorescently labeled short nucleic acid oligomers, which suggest novel allosteric interactions between NC and CA domain enhancing CA dimerization.

Scientific Focus Area: Biomedical Engineering and Biophysics

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