Substrate specificity of the highly alkalophilic bacterial proteinase Esperase: Relation to the X-ray structure

Esperase(R) is a highly alkalophilic bacterial proteinase produced by Bacil lus lentus, The enzyme hydrolyzes peptide bonds comprising the carboxylic g roups of hydrophobic as well as hydrophilic residues in the oxidized insuli n B chain. Some of these bonds are not attacked by other alkaline microbial proteinases. P1-P4 specificity was determined by a series of peptide nitro anilides. The SI recognition loop exhibits a preference for Phe. The "cleft " of the smallest subsite S2 prefers Ala and exhibits low affinity for the larger chain of Leu. S3 is more open than the other subsites and can accept a variety of residues. Hydrophobic interactions predominate in the S4-P4 i nteractions because S4 can accommodate Phe very well. The results character ize Esperase as an endopeptidase with a broader specificity in comparison w ith other microbial serine proteinases. This is probably owing to a more fl exible substrate binding site.