Structure of the coat protein-binding domain of the scaffolding protein from a double-stranded DNA virus

Scaffolding proteins are required for high fidelity assembly of most high T number dsDNA viruses such as the large bacteriophages, and the herpesvirus family. They function by transiently binding and positioning the coat prot ein subunits during capsid assembly. In both bacteriophage P22 and the herp esviruses the extreme scaffold C terminus is highly charged, is predicted t o be an amphipathic alpha-helix, and is sufficient to bind the coat protein , suggesting a common mode of action. NMR studies show that the coat protei n-binding domain of P22 scaffolding protein exhibits a helix-loop-helix mot if stabilized by a hydrophobic core. One face of the motif is characterized by a high density of positive charges that could interact with the coat pr otein through electrostatic interactions. Results from previous studies wit h a truncation fragment and the observed salt sensitivity of the assembly p rocess are explained by the NMR structure. (C) 2000 Academic Press.