EXPRESSION OF THE POLYOMAVIRUS MINOR CAPSID PROTEINS VP2 AND VP3 IN ESCHERICHIA-COLI - IN-VITRO INTERACTIONS WITH RECOMBINANT VP1 CAPSOMERES

The polyomavirus VP2 and VP3 capsid proteins were expressed in Escherichia coli. The majority of the expressed proteins were in an insoluble fraction, and they were extracted and initially purified in 8 M urea before renaturation. Soluble VP2 and VP3 were mixed with purified recombinant WI capsomeres, and their interactions were assayed by immunoprecipitation and ion-exchange chromatography. Coimmunoprecipitation could be demonstrated with antibodies to either VP1 or VP2/VP3. Mixing recombinant VP1 with VP2 and VP3 modified the recognition of VP1 by domain-specific antipeptide antibodies and altered the chromatographic behavior of the individual proteins. Similar results were observed when a truncated VP1 protein, Delta NCOVP1, with 62 amino acids deleted from the carboxy terminus was mixed with VP2/VP3. After the mixing, equilibrium dissociation constants for their binding to either VPI or Delta NCOVP1 were determined to be 0.37 +/- 0.23 mu M for VP2 and 0.18 +/- 0.21 mu M for VP3. These studies demonstrate that the recombinant W2 and VP3 proteins interact with VP1 to affect the biochemical properties of VPI capsomeres and to change the epitope accessibility of VP1 pentamers. These changes may reflect conformational alterations in VP1 capsomeres which-are necessary for viral genome encapsidation.