Conformational rearrangements of bacteriophage T4 lysozyme during its binding to the inhibitor]

The structural changes of bacteriophage T4 lysozyme during its binding to the inhibitor, i. e. disaccharide-tetrapeptide N-acetylglucosaminyl-N-acetylmuraminyl - L - alanyl-gamma-D-glutaminyl - mesodiaminopimelyl-D-alanine) isolated from Escherichia coli cell wall have been studied. During the inhibitor binding to the protein the degree of helicity decreases by approximately 14% as was shown using the circular dichroism technique. The changes in optical properties of tryptophane, tyrosine and phenylalanine residues detected by UV difference and fluorescence spectroscopy have been observed. Based on the experimental data and a comparison of spatial organization of phage T4 lysozyme and chicken egg-white lysozyme made it possible to develop a structural model of phage T4 lysozyme functioning. This model may account for the differences in specificity of action of bacteriophage T4 and chicken egg-white lysozymes and allows to establish the role of the "extra" part of phage lysozyme. According to the model, at the first stage of binding the peptide part of the substrate comes in contact with the "upper" (with respect to the cleft) part of the protein molecule (residues 106--116 and 135--140). This results in rearrangement of the molecule, with opening of the cleft at the second stage. This makes possible the access of the polysaccharide part of the substrate of the active site and a subsequent hydrolysis of the beta (1 leads to 4) glycoside bond.