Role of the C-terminus in folding and oligomerization of bacteriophage T4 gene product 9.

Bacteriophage T4 gene product 9 (gp9) is a structural protein of baseplate that plays a key role at the beginning of the infection process. Biologically active gp9 is a trimer that consists of three domains. It is a convenient model to study folding and oligomerization mechanisms of complex multidomain proteins. The influence of deletions and mutations of several amino acid residues in the C-terminal part of molecule on protein folding, oligomerization, and functional activity has been studied. It was determined that gp9 trimerization occurs post-translationally. It was shown that Gln282 and Ile284 are essential for gp9 trimer stabilization. The disruption of hydrogen bonds formed by Gln282 with Leu203 and Thr205 of neighboring chain has effect not only on interaction between monomers within trimer but also on folding of the polypeptide chain. Tsf (temperature sensitive for folding) and su (suppressor) mutations in the C-terminal region of the polypeptide chain affecting protein folding have been found.