About Enteropeptidase / Enterokinase:
Enteropeptisase is an enzyme which is produced within the duodenum and is key to processes of digestion in humans as well as other animals.
Within humans, the enteropeptidase can be found encoded from the PRSS gene. This is also known as ENTK and is part of chromosome 21q21.
The expression of this enzyme is limited within the proximal small intestine. The protein is often located in enterocytes from the duodenum as well as the proximal jejunum.
After being secreted from within the pancreas into the duodenum, the enzyme meets with trypsinogen and is then activated. It is then that trypsin cleaves and activates various other pancreatic zymogens including prolipases and metalloproteinase zymogens. Through this rapid two-step process, the activity of the digestive hydrolases is then completely confined to the lumen within the intestine.
It does have physiological importance. Evidence of this can be seen from the severe intestinal malabsorption which is triggered by a deficiency of enteropeptidase. The condition can actually be life-threatening. However, it will typically respond to oral supplementation when given with pancreatic extract.
Enteropeptidase has a wide range of interactions and applications. This is due to its specificity. With a fusion protein that contains a C-terminal affinity tag that is linked through this sequence, it can be cleaved to gain the key protein after the protein purification process. Conversely, the N-terminal protein from proteases can also be cleaved before the activation. This can allow it to be mutated to ensure activation with enteropeptidase.
Enteropedtidase activates a group of other enzymes and is seen as an example of how serine proteases function in regulating metabolic pathways through evolution. The serine protease works by catalyzing the hydrolysis of peptide bonds. This differs from other kinases as it does not catalyze transfer through phosphate groups.
It does exhibit activity similar to trypsin cleaving the proteins and one cleavage site. This results in trypsindependent activation of various other pancreatic zymogens. These include chymotrypsinogen, procarboxypeptidase as well as prolapse in the lumen within the gut.
A type II transmembrane serine protease is synthesized as a zymogen, proenteropeptidase and requires the activation of trypsin or duodenal. It is localised to the jejunal mucosa as well as the duodenal of the brush border.
These TTSPs are synthesised in the form of single-chain zymogens and have N-terminal propeptide sequences. These are all of the different lengths. Activated by cleavage at arginine or lysine on the carboxyl side, these form in residues apparent in a highly conserved activation motif.
After being activated, they will typically be predicted to remain membrane-bound. This is due to a conserved disulfide bond which links the catalytic and pro- domains.