Biophysical characterization of polyomavirus minor capsid proteins

The murine polyomavirus encodes three structural proteins, VP1, VP2 and VP3, which together form the viral capsid. The outer shell of this capsid is composed of the major capsid protein VP1, the inner shell consists of VP2 and its N-terminally truncated form VP3. These two minor capsid proteins interact with their identical C-terminal part in the central cavity of VP1 pentamers, building the capsid assembly unit. While the VP1 structure and functions are well studied, VP2 and VP3 are poorly understood. In order to get a detailed insight into the structure and function of the minor capsid proteins, they were produced recombinantly in Escherichia coli as inclusion bodies and refolded in vitro. The success of refolding was strictly dependent on the presence of detergent in the refolding buffer. VP2 and VP3 are monomeric and their structures exhibit a high α-helical content. The function of both proteins could be monitored by complex formation with VP1. Furthermore, we could demonstrate a hemolytic activity of VP2/VP3 in vitro, which fits well into a postulated membrane interaction of VP2 during viral infection.