Analysis of catalytic properties of tripeptidyl peptidase I (TTP-I), a serine carboxyl lysosomal protease, and its detection in tissue extracts using selective FRET peptide substrate

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).

The lysosomal aminopeptidase tripeptidyl peptidase 1 displays increased activity in malignant pancreatic cysts

Incidental detection of pancreatic cysts has increased dramatically over the last decade, but risk stratification and clinical management remain a challenge. Mucinous cysts are precursor lesions to pancreatic cancer, however, the majority are indolent. Current diagnostics cannot identify mucinous cysts that harbor cancer or reliably differentiate these lesions from nonmucinous cysts, which present minimal risk of malignant progression. We previously determined that activity of two aspartyl proteases was increased in mucinous cysts. Using a global protease activity profiling technology, termed multiplex substrate profiling by mass spectrometry (MSP-MS), we now show that aminopeptidase activity is also elevated in mucinous cysts. The serine aminopeptidase, tripeptidyl peptidase 1 (TPP1), was detected by proteomic analysis of cyst fluid samples and quantitation using targeted MS demonstrated that this protease was significantly more abundant in mucinous cysts. In a cohort of 110 cyst fluid samples, TPP1 activity was increased more than 3-fold in mucinous cysts relative to nonmucinous cysts. Moreover, TPP1 activity is primarily associated with mucinous cysts that harbor high-grade dysplasia or invasive carcinoma. Although only 59% accurate for differentiating these lesions, measurement of TPP1 activity may improve early detection and treatment of high-risk pancreatic cysts when used in conjunction with other promising biomarkers.