first Kunitz domain of bikunin and similar proteins
This subfamily includes the N-terminal domain of bikunin (also known as inter-alpha-trypsin inhibitor light chain (ITI-LC) or urinary trypsin inhibitor), a plasma protease inhibitor, that is associated with inflammation and stabilizes the extracellular matrix. It is encoded together with alpha-1-microglobulin (A1M) by an alpha-1-microglobulin/bikunin precursor (AMBP) gene that is tightly controlled by several hepatocyte-enriched nuclear (HEN) factors, and cleaved by a furin-like protease that releases the two mature molecules. Bikunin is a Kunitz-type serine protease inhibitor, found in vertebrate serum and urine, modified by a chondroitin sulfate (CS) chain. The structures of these toxins are similar to that of Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor), showing an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds. Bikunin contains two Kunitz domains; this model represents the first repeat.
Jiyao W et al.(2023). "The conserved domain database in 2023.",