Subtilisin

Proteolytic enzymes (proteases) are omnipresent in nature (see Rawlings et al., Chapter 10, this volume). Subtilisins are a family of serine proteases, i.e. they possess an essential serine residue at the active site. This serine residue is part of a catalytic triad of Aspartate, Histidine and Serine that is very similar to that of mammalian intestinal digestive enzymes, trypsin and chymotrypsin. The subtilisin family, now known as peptidase family S8, is the second largest serine protease family. There are over 200 known members of the family, with the complete amino acid sequence established for the vast majority of them (Siezen and Leunissen, 1997). Proteolytic enzymes that utilize serine in their catalytic triad are quite ubiquitous. They include a wide range of peptidase activities, such as endopeptidases, exopeptidases and oligopeptidases. Over 20 families of serine proteases have been identified and classified as members of 6 clans on the basis of structural and functional similarities. Subtilisins are to be found in archaebacteria, eubacteria, eukaryotes and viruses. The bacterial subtilisins are the subgroup of serine proteases of greater industrial significance and have been studied extensively, with regard to improving their catalytic efficiency and stabilities. As detailed later, those subtilisins produced by selected bacilli have found widespread applications, especially as detergent additives.