Capsid protein composition of reference strains and wild isolates of human astroviruses

Astroviruses are small RNA viruses that are frequently associated with gastroenteritis in humans and animals. Despite much work on the genetic analysis of astrovirus strains, little progress has been made in the characterization of the proteins composing mature virions. We have analyzed the capsid protein composition of the reference strains and several wild isolates of human astroviruses using high-resolution polyacrylamide gradient gels. For reference strains of the seven serotypes analyzed, a consistent pattern of three infection-specific proteins—designated P1, P2, and P3—was generally observed. The strains could be divided into two groups, based upon the reactivity of these proteins in immune precipitation assays that used homologous rabbit serum. One group included reference types 1–4 for which all three proteins were precipitated by homologous rabbit sera; for the other group, types 5–7, only proteins P2 and P3 were precipitated. When wild isolates from around the world were compared to the reference strains, a correlation between genetic type and the pattern of protein sizes and immune reactivity was observed for strains of the common types (1–4). Strains of types 2 and 4 consistently exhibited P3 proteins larger than those of types 1 and 3. Unusual patterns of proteins or immune reactivity were detected in strains of types 5–7, indicating that there may be incomplete processing of the capsid precursor during growth in cell culture.