Analysis of minimal sequences on JC virus VP1 required for capsid assembly

Human JC virus (JCV) belongs to the family of Polyomaviridae. The viral capsid is composed of 72 capsomeres. Five VP1 molecules make up a capsomere structure. To investigate the minimal sequences on JCV VP1 polypeptide required for capsid assembly, the first 12 (Delta N12) and 19 (Delta N19) amino acids at the N-terminus and the last 16 (Delta C16), 17 (Delta C17), and 31 (Delta C31) amino acids at the C-terminus of VP1 were truncated and expressed in E. coli. The VP1 proteins of Delta N12 and Delta C16 were able to self-assemble into a virus-like particle similar to that of wild-type (WT) VP1. However, the mutant proteins of Delta N19, Delta C17, and Delta C31 formed a pentameric capsomere structure as demonstrated by a 10-50% sucrose gradient centrifugation and electron microscopy. These results suggest that the 12 amino-terminal and 16 carboxy-terminal amino acids of VP1 are dispensable for the formation of virus-like particles, and further truncation at either end of VP1 leads to the loss of this property.