3-DIMENSIONAL STRUCTURAL-ANALYSIS OF RECOMBINANT ROTAVIRUS-LIKE PARTICLES WITH INTACT AND AMINO-TERMINAL-DELETED VP2 - IMPLICATIONS FOR THEARCHITECTURE OF THE VP2 CAPSID LAYER

Rotaviruses are the leading cause of severe infantile gastroenteritis worldwide, These viruses are large, complex icosahedral particles cons isting of three concentric capsid layers enclosing a genome of eleven segments of double-stranded RNA (dsRNA), The amino terminus of the inn ermost capsid protein VP2 possesses a nonspecific single-stranded RNA and dsRNA binding activity, and the amino terminus is also essential f or the incorporation of the polymerase enzyme VP1 and guanylyltransfer ase VP3 into the core of the virion, Bio-chemical and structural studi es have suggested that VP2, and especially the amino terminus, appears to act as a scaffold for proper assembly of the components of the vir al core, To locate the amino terminus of VP2 within the core, we have used electron cryomicroscopy and image reconstruction to determine the three-dimensional structures of recombinant virus-like particles that contain either full-length or amino-terminal-deleted forms of VP2 coe xpressed with the intermediate capsid protein VP6, A comparison of the se structures indicates two significant changes along the inner surfac e of VP2 in the structure lacking the amino terminus: a loss of mass a djacent to the fivefold axes and a redistribution of mass along the fi vefold axes, Examination of the VP2 layer suggests that the proteins a re arranged as dimers of 120 quasi-equivalent molecules, with each dim er extending between neighboring fivefold axes, Our results indicate t hat the amino termini of both quasi-equivalent VP2 molecules are locat ed near the icosahedral vertices.