CASPAR CARBOXYLATES - THE STRUCTURAL BASIS OF TOBAMOVIRUS DISASSEMBLY

Carboxylate groups have been known for many years to drive the disasse mbly of simple viruses, including tobacco mosaic virus (TMV). The iden tities of the carboxylate groups involved and the mechanism by which t hey initiate disassembly have not, however, been clear. Structures hav e been determined at resolutions between 2.9 and 3.5 Angstrom for five tobamoviruses by fiber diffraction methods. Site-directed mutagenesis has also been used to change numerous carboxylate side chains in TMV to the corresponding amides. Comparison of the stabilities of the vari ous mutant viruses shows that disassembly is driven by a much more com plex set of carboxylate interactions than had previously been postulat ed. Despite the importance of the carboxylate interactions, they are n ot conserved during viral evolution. Instead, it appears that during e volution, patches of electrostatic interaction drift across viral subu nit interfaces. The flexibility of these interactions confers a consid erable advantage on the virus, enabling it to change its surface struc ture rapidly and thus evade host defenses.