Seprase or Fibroblast activation protein (FAP) is an integral membrane serine peptidase, which has been shown to have gelatinase activity. Seprase has a dual function in tumour progression. The proteolytic activity of Seprase has been shown to promote cell invasiveness towards the ECM and also to support tumour growth and proliferation. Seprase appears to act as a proteolytically active 170-kDa dimer, consisting of two 97-kDa subunits. It is a member of the group type II integral serine proteases, which include dipeptidyl peptidase IV (DPPIV/CD26) and related type II trans-membrane prolyl serine peptidases, which exert their mechanisms of action on the cell surface. DPPIV and Seprase exhibit multiple functions due to their abilities to form complexes with each other and to interact with other membrane-associated molecules. Localization of these protease complexes at cell surface protrusions, called invadopodia, may have a prominent role in processing soluble factors and in the degradation of extracellular matrix components that are essential to the cellular migration and matrix invasion that occur during tumour invasion, metastasis and angiogenesis.-3 -

ABBREVIATIONSAMC, 7-amino-4-methylcoumarin; BCA, bicinchoninic acid; CPC, calcium phosphate cellulose; DFP, diisopropylfluorophosphate; FPLC, fast protein liquid chromatography; HIC, hydrophobic interaction chromatography; PO, prolyl oligopeptidase; TFA, trifluoroacetic acid; Z, N-benzyloxycarbonyl; ZIP, Z-Pro-prolinal-insensitive Z-Gly-Pro-AMC-hydrolysing peptidase. ABSTRACTThe study and identification for the first time of a soluble form of a Seprase activity from bovine serum is presented. To date, this activity has only been reported to be an integral membrane protease but has been known to shed from its membrane. The activity was purified 30,197-fold to homogeneity, using a combination of column chromatographies, from bovine serum. Inhibition by DFP, resulting in an IC 50 of 100nM confirms classification as a serine protease. The protease after separation and visualisation by native PAGE was subjected to tryptic digestion and the subsequent peptides sequenced. Each peptide sequenced was found to be present in the primary structure of Seprase/Fibroblast Activation Protein (FAP), a serine gelatinase specific for proline-containing peptides and macromolecules. Substrate specificity studies using kinetic, RP-HPLC and LC-MS analysis of synthetic peptides suggest that this peptidase has an extended substrate-binding region in addition to the primary specificity site S 1 . This analysis revealed at least five subsites to be involved in enzyme-substrate binding, 2 with the smallest peptide cleaved being a tetrapeptide. A proline residue in position P 1 was absolutely necessary therefore showing high primary substrate specificity for the Pro-X bond, while a preference for a hydrophobic residue at the C-terminal end of the scissile bond (P 1 ʹ′) was evident. The enzyme also showed complete insensitivity to the prolyl oligopeptidase specific inhibitors, JTP-4819, Fmoc-Ala-pyrrCN and Z-Phe-Pro-BT. To date, no physiological substrate has clearly been defined for this protease but its ability to effectively degrade gelatin suggests a candidate protein substrate in vivo and a possible role in extracellular matrix protein degradation.