Functional role of the N-terminal domain of bacteriophage T4 gene product 11

Bacteriophage T4 late gene product 11 (gp11), the three-dimensional structure of which has been solved by us to 2.0 A resolution, is a part of the virus' baseplate. The gp11 polypeptide chain consists of 219 amino acid residues and the functionally active protein is a three-domain homotrimer. In this work, we have studied the role of gp11 N-terminal domain in the formation of a functionally active trimer. Deletion variants of gp11 and monoclonal antibodies recognizing the native conformation of gp11 trimer have been selected. Long deletions up to a complete removal of the N-terminal domain, containing 64 residues, do not affect the gp11 trimerization, but considerably change the protein structure and lead to the loss of its ability to incorporate into the baseplate. However, the deletion of the first 17 N-terminal residues results in functionally active protein that can complete the 11(-)-defective phage particles in in vitro complementation assay. This region of the polypeptide chain is probably essential for gp11-gp10 stable complex formation at the early stages of phage baseplate assembly in vivo. A study of the gp10 deletion variants suggests that the central domain of gp10 trimer is responsible for the interaction with gp11.