Anti-GP9 monoclonal antibody, clone HS-Q [OC515]

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.

Gene product 9 (gp9, 288 amino acid residues per monomer, molecular weight 30.7 kD) of bacteriophage T4 triggers the baseplate reorganization and the sheath contraction after interaction of the long tail fibers with the receptors of the bacterial cell. In this work we have produced the recombinant protein and determined that gp9 is a stable homotrimer and active in in vitro complementation assay completing the defective phage particles which lack gp9. According to CD-spectroscopy data, the gp9 polypeptide chain contains 65-73% beta-structure and 11-16% alpha-helical segments, this being in good agreement with secondary structure prediction results. Additionally, we have constructed a set of plasmid vectors for expression of gp9 deletion mutants. The fragments with consecutive truncations of the N-terminus of the molecule, as well as the full-length protein, are trimers resistant to SDS treatment and decrease infective phage particle formation in in vitro complementation assay with native gp9. The deletion of the molecule C-terminal region results in failure of trimerization and decreases the stability of the protein.