Zinc protease of Bacillus subtilis var. amylosacchariticus: construction of a three-dimensional model and comparison with thermolysin.

The active site structure of the Zn-containing neutral protease from Bacillus subtilis var. amylosacchariticus (BANP) was predicted by computer-aided modeling on the basis of the three-dimensional structure of thermolysin (TLN). As expected from the high homology in amino acid sequence of the two enzymes, the overall folding of BANP was very similar to that of TLN. Glu144, Tyr158, and His228 of BANP were located near the active site Zn ion, to which three amino acid residues, His143, His147, and Glu167, were coordinated. This model is supported by the previous results that chemical modifications of Tyr158 and photooxidation of His228 of BANP markedly affect the proteolytic activity of the enzyme. Interestingly, BANP was found to be significantly less sensitive to metalloprotease inhibitors such as phosphoramidon and talopeptin. From a comparison of the enzyme-inhibitor complex models between BANP and thermolysin, it is suggested that replacement of Thr129 in TLN by Phe130 in BANP is related to difference in inhibitor sensitivity between BANP and TLN.