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.

• Keywords: Serine Protease Inhibitor, Semen
• View this protein's PDB entry as 2BUS
• View this protein's SwissProt entry as IAC2_BOVIN
• References:
  • M.P. Williamson, T.F. Havel, K. Wuthrich
    Solution Conformation of Proteinase Inhibitor IIA From Bull Seminal Plasma by 1H Nuclear Magnetic Resonance and Distance Geometry.
    J. Mol. Biol. 182:295 (1985)
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  • M.P. Williamson, D. Marion, K. Wuthrich
    Secondary Structure in the Solution Conformation of the Proteinase Inhibitor IIA From Bull Seminal Plasma by Nuclear Magnetic Resonance.
    J. Mol. Biol. 173:341 (1984)
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  • P. Strop, G. Wider, K. Wuthrich
    Assignment of the 1H Nuclear Magnetic Resonance Spectrum of the Proteinase Inhibitor IIA From Bull Seminal Plasma by Two-Dimensional Nuclear Magnetic Resonance at 500 MHz.
    J. Mol. Biol. 166:641 (1983)
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  • P. Strop, K. Wuthrich
    Characterization of the Proteinase Inhibitor IIA From Bull Seminal Plasma by 1H Nuclear Magnetic Resonance. Stability, Amide Proton Exchange and Mobility of Aromatic Residues.
    J. Mol. Biol. 166:631 (1983)
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