Stem Mutants in the N-terminal Domain of the Phage P22 Tailspike Protein

The P22 tailspike protein is an intensely studied protein whose structure and sequence has been described. However, a study, describing important protein interactions related to its function at the N-terminal domain, has been lacking. The P22 tailspike protein (TSP) consists of three identical polypeptide chains of 666aa. The first 108 of the 666aa in the P22 TSP form a trimeric N-terminal domain (NTD). Each of the three chains of the trimeric NTD contributes to the formation of a dome-like structure. Our studies suggest that a short stretch of amino acids located within the first fifteen amino acids of the P22 TSP NTD is critical for the stability of the dome structure formed by the first 108aa of the P22 TSP NTD. The first 23aa are located within this dome-like structure and have been dubbed the “stem” of the NTD. Although amino acid residues in the first 15aa (lower stem) are critical, deletion analysis and in vitro assembly studies implicate the rest of the stem in additional stabilizing interactions. Our studies implicate a common protein-protein interaction motif made up of interchain hydrophobic contacts between adjacent chains