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 purified from the fruiting bodies of the edible mushroom, Lentinus edodes, by buffer extraction and affinity chromatography on immobilized anhydrotrypsin. The protein simultaneously inhibits bovine beta-trypsin and alpha-chymotrypsin 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 two well-separated peaks on reversed-phase HPLC, one of which is inhibitory-active and the other inactive, and they are interconvertible under folding/unfolding conditions. Among the mammalian and microbial serine proteinases examined, including human enzymes of blood coagulation and fibrinolysis, activated factor XI was inhibited by the Lentinus proteinase inhibitor. Chemical modification studies suggest involvement of one or more arginine residues in the inhibition of trypsin. The complete primary structure composed of 142 amino acids with an acetylated N-terminus was determined by protein analysis. The theoretical molecular mass (15999.2) from the sequence is close to the experimental value of 15999.61 +/- 0.61 determined by mass spectrometry. Although there are no apparently homologous proteinase inhibitors in the protein database, there is a rather striking similarity to the propeptide segment of a microbial serine proteinase, as well as to the N-terminal region of the mature enzyme.