INTERSUBUNIT INTERACTIONS ALLOWING A CARBOXYLATE MUTANT COAT PROTEIN TO INHIBIT TOBAMOVIRUS DISASSEMBLY

Tobacco mosaic tobamovirus (TMV) coat protein (CP) mutant E50Q lacks a repulsive intersubunit carboxylate group and can effectively inhibit the disassembly of wild-type TMV (Culver et al., 1995, Virology 206,72 4). To investigate the ability of this mutant CP to block disassembly, a series of second-site amino acid substitutions were added to the E5 0Q CP. These second-site mutations were designed to disrupt specific i ntersubunit stabilizing interactions involving hydrophobic or polar re sidues, salt bridges, and CP-RNA contacts. Results showed substitution s disrupting intersubunit interactions that face the disassembling sur face of the virion dramatically reduced the ability of CP E50Q to inhi bit TMV disassembly. Substitutions that disrupted the CP inner loop, R NA binding capabilities, or intersubunit interactions that faced away from the disassembling surface did not dramatically interfere with CP E50Q's ability to inhibit disassembly. Taken together, these findings suggest that intersubunit interactions made by 5' terminal E50Q subuni ts, not associated with RNA, provide the stabilizing forces that preve nt virion disassembly. The role of these stabilizing interactions in T MV disassembly and their potential use for creating disassembly inhibi ting CPs are discussed. (C) 1998 Academic Press.