Proteinase inhibitor IIA

Proteinase inhibitor IIA is a protein from bull seminal plasma which inhibits acrosin, trypsin, and chymotrypsin. It is thought that while this protein can inhibit proteinases, it may also play a role in the protection of tissues against the inflammatory process as well as help in the control of fertilization. It is very similar to the kazal family of serine protease inhibitors.
Proteinase inhibitor IIA is a 57 amino acid residue long protein. It contains three disulfide bridges; Cys7-Cys39, Cys17-Cys36, and Cys25-Cys57 which are shown here in white. The three antiparallel beta sheets are colored gold. A right-handed alpha helix is shown in green, and a 310 alpha helix is shown in red.

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