The structure of Bowman-Birk type protease inhibitor A-II from peanut (Arachis hypogaea) at 3.3 A resolution.

The structure of Bowman-Birk type protease inhibitor (A-II from peanut) is described at 3.3 A resolution. The molecules form a tetramer with 222 local symmetry in our crystals. Each monomer has an elongated shape with approximate dimensions of 45 X 15 X 15 A and consists of two distinct domains. The three-dimensional structures of the two domains are similar and are related by the intramolecular approximate twofold rotation axis. The two independent protease binding sites protrude from the molecular body on opposite sides. A scheme for the molecular evolution of the double-headed Bowman-Birk type protease inhibitors is proposed, based on the three-dimensional structure.