GALCIT Colloquium

The capacity of the self-assembling viral shells (capsids) to respond structurally and mechanically to physical and chemical stimuli makes them of a target of interest for the design of advanced materials.  Many viruses undergo "maturation" transitions, exhibiting gross morphological changes in coordination with local symmetry-breaking motions of the protein building blocks.  These observations form a puzzle: What are the driving forces for these changes?  What is the origin of symmetry-breaking, and what biological advantages does it confer?  I will address these questions with a continuum theory that models viral maturation as analogous to a martensitic phase transition.  With this model we can understand conformational changes as being driven by elastic interactions among defects in the crystalline protein lattice.  We find that the presence of soft conformational modes in the protein building blocks can promote assembly.  Furthermore, the tendency of biological molecules to generate symmetric structures competes with the tendency to break symmetry in order to achieve specific functional goals.  The model also forms a framework for extending continuum theory to cross length scales of macromolecular discreteness.