ricin B-type lectin domain, beta-trefoil fold, found in Macrocypins from Macrolepiota procera
Macrocypins comprise a family of cysteine protease inhibitors from the basidiomycete Macrolepiota procera (parasol mushroom) that possess a beta-trefoil fold, the hallmark of Kunitz-type inhibitors. Macrocypins are effective inhibitors of papain and cysteine cathepsin endopeptidases, and also inhibit cathepsins B and H, which exhibit both exopeptidase and endopeptidase activities. The ricin B-type lectin domain shows a beta-trefoil fold, which is characterized by 12 beta strands folded into three similar trefoil subdomains (alpha, beta, and gamma) associated to give an overall structure with pseudo-3-fold symmetry. Each subdomain bears a potential sugar binding site.
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