Enteropeptidase

Enteropeptidase (also called enterokinase) is an enzyme produced by cells of the duodenum and involved in human digestion. It is secreted from intestinal glands (the crypts of Lieberkühn) following the entry of ingested food passing from the stomach. Enteropeptidase converts trypsinogen (a zymogen) into its active form trypsin, resulting in the subsequent activation of pancreatic digestive enzymes.

Enteropeptidase is a serine protease consisting of a disulfide-linked 82–140 kDa heavy chain which anchors enterokinase in the intestinal brush border membrane and a 35–62 kDa light chain which contains the catalytic subunit. Enteropeptidase is a part of the chymotrypsin-clan of serine proteases, and is structurally similar to these proteins.

Activity
Despite its alternative name, enteropeptidase is a serine protease which catalyses the hydrolysis of peptide bonds in proteins. Enteropeptidase exhibits trypsin-like activity, cleaving proteins following a lysine at a specific cleavage site (Asp-Asp-Asp-Asp-Lys). As the pro-region of trypsinogen contains this sequence, enteropeptidase catalyses its activation in vivo:

trypsinogen → trypsin + pro-region (Val-Asp-Asp-Asp-Asp-Lys)

Genetics
In humans, enteropeptidase is encoded by the PRSS7 gene (also known as ENTK) on chromosome 21q21. Some nonsense and frameshift mutations in this gene lead to a rare recessive disorder characterised by severe failure to thrive in affected infants, due to enteropeptidase deficiency.

Applications
Enteropeptidase's specificity makes it an ideal tool in biochemical applications; a fusion protein containing a C-terminal tag (such as poly-His) linked by this sequence can be cleaved by enteropeptidase to obtain the target protein following protein purification. Alternatively, the N-terminal pro-sequence of proteases which must be cleaved prior to activation can be mutated to enable activation with enteropeptidase.