"Local rules" theory applied to polyomavirus polymorphic capsid assemblies

The papovaviruses are nonenveloped dsDNA viruses whose capsids are characterized by a non-quasi-equivalent bonding pattern in which 72 pentameric capsomeres occupy positions having either five or six neighboring capsomeres. The local rules theory of Berger et al. (1994, Proc. Natl. Acad. Sci. USA, 91, 7732-7736), previously developed to explain aspects of icosahedral capsid assembly, has been applied to the papovavirus geometry. Local rules describe capsid symmetry patterns in terms of the local interactions of assembly units, such as coat proteins or capsomeres. Polymorphic assemblies, including T = 1 icosahedral, dodecahedral, spiral, and tubular structures of the polyomavirus VP1 protein, can be induced by specific mutations or changes in the solvent conditions during in vitro assembly of the recombinant coat protein. Local rules models were developed to model the wild-type capsid and several polymorphic assemblies. Some assemblies corresponded to structures modeled by small deviations from wild-type local rules. We conclude that aspects of polyomavirus assembly are consistent with local rules models, although they do not explain all polymorphisms. These results may provide insights into the nature of papovavirus assembly, constraints on assembly pathways, and strategies for disrupting assembly.