Pepstatin‐insensitive carboxyl proteinase: A biochemical marker for late lysosomes inAmoeba proteus

Serine-Carboxyl Peptidases, Sedolisins: From Discovery to Evolution

Sedolisin is a proteolytic enzyme, listed in the peptidase database MEROPS as a founding member of clan SB, family S53. This enzyme, although active at low pH, was originally shown not to be inhibited by an aspartic peptidase specific inhibitor, S-PI (pepstatin Ac). In this Perspective, the S53 family is described from the moment of original identification to evolution. The representative enzymes of the family are sedolisin, kumamolisin, and TPP-1. They exhibit the following unique features. (1) The fold of the molecule is similar to that of subtilisin, but the catalytic residues consist of a triad, Ser/Glu/Asp, that is unlike the Ser/His/Asp triad of subtilisin. (2) The molecule is expressed as a pro-form composed of the amino-terminal prosegment and the active domain. Additionally, some members of this family have an additional, carboxy-terminal prosegment. (3) Their optimum pH for activity is in the acidic region, not in the neutral to alkaline region where subtilisin is active. (4) Their distribution in nature is very broad across the three kingdoms of life. (5) Some of these enzymes from fungi and bacteria are pathogens to plants. (6) Some of them have significant potential applications for industry. (7) The lack of a TPP-1 gene in human brain is the cause of incurable juvenile neuronal ceroid lipofuscinosis (Batten's disease).

Ser475, Glu272, Asp276, Asp327, and Asp360 are involved in catalytic activity of human tripeptidyl-peptidase I

Tripeptidyl-peptidase I (TPP I) is a lysosomal aminopeptidase that sequentially removes tripeptides from small polypeptides and also shows a minor endoprotease activity. Mutations in TPP I are associated with a fatal lysosomal storage disorder--the classic late-infantile form of neuronal ceroid lipofuscinoses. In the present study, we analyzed the catalytic mechanism of the human enzyme by using a site-directed mutagenesis. We demonstrate that apart from previously identified Ser475 and Asp360, also Glu272, Asp276, and Asp327 are important for catalytic activity of the enzyme. Involvement of serine, glutamic acid, and aspartic acid in the catalytic reaction validates the idea, formulated on the basis of significant amino acid sequence homology and inhibition studies, that TPP I is the first mammalian representative of a growing family of serine-carboxyl peptidases.