Surface for catalysis by poliovirus RNA-dependent RNA polymerase.

The poliovirus RNA-dependent RNA polymerase, 3Dpol, replicates the viral genomic RNA on the surface of virus-induced intracellular membranes. Macromolecular assemblies of 3Dpol form linear arrays of subunits that propagate along a strong protein-protein interaction called interface-I, as was observed in the crystal structure of wild-type poliovirus polymerase. These "filaments" recur with slight modifications in planar sheets and, with additional modifications that accommodate curvature, in helical tubes of the polymerase, by packing filaments together via a second set of interactions. Periodic variations of subunit orientations within 3Dpol tubes give rise to "ghost reflections" in diffraction patterns computed from electron cryomicrographs of helical arrays. The ghost reflections reveal that polymerase tubes are formed by bundles of four to five interface-I filaments, which are then connected to the next bundle of filaments with a perturbation of interface interactions between bundles. While enzymatically inactive polymerase is also capable of oligomerization, much thinner tubes that lack interface-I interactions between adjacent subunits are formed, suggesting that long-range allostery produces conformational changes that extend from the active site to the protein-protein interface. Macromolecular assemblies of poliovirus polymerase show repeated use of flexible interface interactions for polymerase lattice formation, suggesting that adaptability of polymerase-polymerase interactions facilitates RNA replication. In addition, the presence of a positively charged groove identified in polymerase arrays may help position and stabilize the RNA template during replication.