Trypsin-3, also known as Trypsin III, brain trypsinogen, Serine protease 3 and PRSS3, is a secreted protein that belongs to the peptidase S1 family. Trypsin-3 PRSS3 is expressed is in pancreas and brain. It contains one peptidase S1 domain. Trypsin-3 PRSS3 can degrade intrapancreatic trypsin inhibitors that protect against CP. Genetic variants that cause higher mesotrypsin activity might increase the risk for chronic pancreatitis (CP). A sustained imbalance of pancreatic proteases and their inhibitors seems to be important for the development of CP. The trypsin inhibitor-degrading activity qualified PRSS3 as a candidate for a novel CP susceptibility gene. Trypsin-3 PRSS3 has been implicated as a putative tumor suppressor gene due to its loss of expression, which is correlated with promoter hypermethylation, in esophageal squamous cell carcinoma and gastric adenocarcinoma.
MASP3 is a member of the MASPs involved in mannan-binding lectin (MBL) complement pathway. The MBL pathway is initiated by the binding of MBL to specific carbohydrate structures found on the surface of a variety of microorganisms. Activation of the complement pathway via MBL is initiated by specific MASPs. Three MASPs have been identified and all have domain structures similar to those of C1r and C1s with a heavy chain (chain A) and a light chain (chain B). Chain A is composed of CUB1, EGF, CUB2, CCP1 and CCP2 while chain B corresponds to the catalytic domain found in many serine proteases. MASP1 and MASP3 are two alternatively spliced products of a single gene, which contain the same A chains but entirely different B chains. Distinct MASPs found in different MBL oligomers may have different biological activities. For example, MASP3, found together with MASP2, downregulates the C4 and C2 cleaving activity of MASP2. The protease activity of MASP3 is first revealed here using rhMASP3CD, which is inhibited by serine protease inhibitors such as Ecotin and AEBSF.