Atomic structure of the major capsid protein of rotavirus: implications for the architecture of the virion

The structural protein VP6 of rotavirus, an important pathogen responsible for severe gastroenteritis in children, forms the middle layer in the tripl e-layered viral capsid, Here we present the crystal structure of VP6 determ ined to 2 Angstrom resolution and describe its interactions with other caps id proteins by fitting the atomic model into electron cryomicroscopic recon structions of viral particles. VP6, which forms a tight trimer, has two dis tinct domains: a distal beta -barrel domain and a proximal alpha -helical d omain, which interact with the outer and inner layer of the virion, respect ively. The overall fold is similar to that of protein VP7 from bluetongue v irus, with the subunits wrapping about a central 3-fold axis. A distinguish ing feature of the VP6 trimer is a central Zn2+ ion located on the 3-fold m olecular axis. The crude atomic model of the middle layer derived from the fit shows that quasi-equivalence is only partially obeyed by VP6 in the T = 13 middle layer and suggests a model for the assembly of the 260 VP6 trime rs onto the T = 1 viral inner layer.