(74h) Elucidating a Network of Interactions That Drive Large-Scale and Pleomorphic Protein Assemblies during Viral Budding

Authors: 
Pak, A. J., The University of Chicago
Grime, J. M. A., The University of Chicago
Voth, G. A., The University of Chicago
Complex enveloped viruses have an intriguingly robust ability to assemble, package, and release viral materials from host cells as virions to spread infection. Human immunodeficiency virus type-1 (HIV-1) is one paradigmatic example in which a structural polyprotein called Gag is known to self-assemble into a protein lattice at the cell membrane interface while coordinating viral ribonucleic acid (RNA). Interestingly, cryo-electron tomography studies have revealed that the protein lattice contains local hexameric order while the complete lattice, which includes up to 5000 copies of Gag, exhibits notable pleomorphism. The pleomorphic nature of this so-called “immature lattice” has been hypothesized as an essential intermediate during the viral lifecycle, yet the molecular mechanisms that dictate viral assemblies and resultant morphologies have remained unclear. To address these questions, we developed a series of coarse-grained (CG) models for Gag, lipids, and viral RNA to directly probe this highly dynamical process. Initial studies revealed that Gag multimerization into hexameric lattices is largely driven by weak anisotropic interactions at the capsid-spacer peptide 1 interface. However, this process is necessarily regulated by scaffolding from viral RNA and membrane deformation during budding. These insights were then used to design collective variables that could be biased (e.g., with metadynamics) to overcome entropic barriers during protein assembly. As a result, we investigated virion-scale assembly and identified a resonant relationship between lattice pleomorphism and membrane fluctuations. Taken together, our results provide fundamental biophysical understanding into supramolecular protein assembly and suggest potential biomedical strategies to combat viral progression.