Transformation of a fragment of beta-structural bacteriophage T4 adhesin to stable alpha-helical trimer

Gene product 12 of bacteriophage T4, adhesin, serves to adhere the virus to host cells. Adhesin is a fibrous homotrimer, and a novel tertiary structure element, a beta-helix, is supposed to be a major structural feature of this protein. We have constructed two truncated gp12 mutants, 12N1 and 12N2, containing 221 and 135 N-terminal residues, respectively. When expressed in E. coli cells, these gp12 fragments formed labile beta-structural trimers. Another hybrid protein, 12FN, containing 179 N-terminal amino acid residues of gp12 fused to the C-terminal domain (31 amino acids) of T4 fibritin, was shown to have a trimeric proteolytically resistant alpha-helical structure. This structure is probably similar to that of fibritin, which has a triple alpha-helical coiled-coil structure. Hence, we have demonstrated the possibility of global transformation of fibrous protein structure using fusion with a C-terminal domain that initiates trimerization.