Physics (Internal)

Viruses as adaptable containers--modeling the simultaneous assembly and encapsulation of flexible polymers and solid nanoparticles by viral capsid proteins.

This event is part of the Biophysics/Condensed Matter Seminar Series.

Abstract:
During the replication of many viruses, hundreds to thousands of protein subunits assemble around the viral nucleic acid to form a protein shell called a capsid. Most viruses form one particular structure with astonishing fidelity; yet, recent experiments demonstrate that capsids can assemble with different sizes and morphologies to accommodate nucleic acids or synthetic cargoes such as nanoparticles and inorganic polyelectrolytes. The assembly mechanisms that enable this combination of adaptability and precision are poorly understood.

In this talk, I will present simulations that explore the simultaneous assembly and encapsidation of rigid nanoparticles and flexible polymers. The simulations elucidate mechanisms by which subunits faithfully form empty capsids with a single morphology, but adaptively assemble into different icosahedral morphologies around nanoparticles with different diameters. The model predicts that adaptation is only successful at moderate nanoparticle-subunit interaction strengths; with strong interactions assembly is frustrated by metastable partial capsids whose curvature is incommensurate with the nanoparticle geometry. We compare the simulation results to recent experiments in which brome mosaic virus capsid proteins assemble around functionalized nanoparticles. For the case of assembly around a flexible polymer, we determine the maximum polymer length that can be dynamically encapsidated and the polymer length around which assembly is most effective. We will discuss how predictions for the polymer-length dependence of assembly rates can be tested with single molecule experiments.