The three dimensional structure of the lysozyme from bacteriophage T4.

The three dimensional structure of the lysozyme from bacteriophage T4 has been determined from a 2.5 A resolution electron density map. About 60% of the molecule is in a helical conformation and there is one region consisting of antiparallel beta-structure. The polypeptide backbone folds into two distinct lobes linked in part by a long helix. In the region between the two lobes, there is a cleft which deepens into a hole or cavity, about 6-8 A in diameter, extending from one side of the molecule to the other. This opening is closed off by side chains which extend to within 3-5 A of each other. A number of mutant lysozymes in which residues in the vicinity of the opening are modified have markedly reduced catalytic activity, suggesting that this region of the molecule may be catalytically important. The three dimensional structure of T4 phage lysozyme is quite different from that of hen egg-white lysozyme although it is not clear at this time whether or not the mechanisms of catalysis of the respective enzymes are related.