The inhibitory properties and primary structure of a novel serine proteinase inhibitor from the fruiting body of the basidiomycete, Lentinus edodes

A novel proteinase inhibitor, Lentinus proteinase inhibitor, has been purif ied from the fruiting bodies of the edible mushroom, Lentinus edodes, by bu ffer extraction and affinity chromatography on immobilized anhydrotrypsin. The protein simultaneously inhibits bovine beta-trypsin and alpha-chymotryp sin at independent sites, with apparent dissociation constants of 3.5 x 10( -10) M and 4 x 10(-8) M, respectively. The purified protein is eluted as tw o well-separated peaks on reversed-phase HPLC, one of which is inhibitory-a ctive and the other inactive, and they are interconvertible under folding/u nfolding conditions. Among the mammalian and microbial serine proteinases e xamined, including human enzymes of blood coagulation and fibrinolysis, act ivated factor XI was inhibited by the Lentinus proteinase inhibitor. Chemic al modification studies suggest involvement of one or more arginine residue s in the inhibition of trypsin. The complete primary structure composed of 142 amino acids with an acetylated N-terminus was determined by protein ana lysis. The theoretical molecular mass (15999.2) from the sequence is close to the experimental value of 15999.61 +/- 0.61 determined by mass spectrome try. Although there are no apparently homologous proteinase inhibitors in t he protein database. there is a rather striking similarity to the propeptid e segment of a microbial serine proteinase, as well as to the N-terminal re gion of the mature enzyme.