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==Overview==

BACKGROUND: The large plasma proteinase inhibitors of the alpha, 2-macroglobulin superfamily inhibit proteinases by capturing them within a, central cavity of the inhibitor molecule. After reaction with the, proteinase, the alpha-macroglobulin-proteinase complex binds to the, alpha-macroglobulin receptor, present in the liver and other tissues, and, becomes endocytosed and rapidly removed from the circulation. The complex, binds to the receptor via recognition sites located on a separate domain, of approximately 138 residues positioned at the C terminus of the, alpha-macroglobulin subunit. RESULTS: The crystal structure of the, receptor-binding domain of bovine alpha 2-macroglobulin (bRBD) has been, determined at a resolution of 1.9 A. The domain primarily comprises a, nine-strand beta structure with a jelly-roll topology, but also contains, two small alpha helices. CONCLUSIONS: The surface patch responsible for, receptor recognition is thought to involve residues located on one of the, two alpha helices of the bRBD as well as residues in two of the beta, strands. Located on this alpha helix are two lysine residues that are, important for receptor binding. The structure of bRBD is very similar to, the approximately 100-residue C-terminal domain of factor XIII, a, transglutaminase from the blood coagulation system.

==About this Structure==

[[Category: receptor binding domain]]