Proteinase inhibitor I2, Kunitz metazoa <p>The majority of the sequences having this domain belong to the MEROPS inhibitor family I2, clan IB; the Kunitz/bovine pancreatic trypsin inhibitor family, they inhibit proteases of the S1 family [<cite idref="PUB00014133"/>] and are restricted to the metazoa with a single exception: <taxon tax_id="28321">Amsacta moorei entomopoxvirus</taxon>. They are short (~50 residue)alpha/beta proteins with few secondary structures. The fold is constrainedby 3 disulphide bonds. The type example for this family is aprotinin (bovine pancreatic trypsin inhibitor) [<cite idref="PUB00003271"/>] (or basic protease inhibitor), but the family includes numerous other members[<cite idref="PUB00005362"/>, <cite idref="PUB00003421"/>, <cite idref="PUB00004837"/>, <cite idref="PUB00005002"/>], such as snake venom basic protease; mammalian inter-alpha-trypsininhibitors; trypstatin, a rodent mast cell inhibitor of trypsin; a domainfound in an alternatively-spliced form of Alzheimer's amyloid beta-protein;domains at the C-termini of the alpha(1) and alpha(3) chains of type VIIand type VI collagens; and tissue factor pathway inhibitor precursor.</p>