Structure and folding of bacteriophage T4 gene product 9 triggering infection. I. Production and properties of recombinant protein

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 recep tors of the bacterial cell. In this work we have produced the recombinant p rotein and determined that gp9 is a stable homotrimer and active in in vitr o 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 goo d agreement with secondary structure prediction results. Additionally, we h ave constructed a set of plasmid vectors for expression of gp9 deletion mut ants. The fragments with consecutive truncations of the N-terminus of the m olecule, as well as the full-length protein, are trimers resistant to SDS t reatment and decrease infective phage particle formation in in vitro comple mentation assay with native gp9. The deletion of the molecule C-terminal re gion results in failure of trimerization and decreases the stability of the protein.