Amino acid sequence and characterization of a nuclease (nuclease Le3) from Lentinus edodes

The fruit body of shiitake (Lentinus edodes) produces two acid nucleases, nuclease Le1 and nuclease Le3, both of which are thought to be candidates for the enzyme that produces a flavorful substance, 5'-GMP, and the primary structure of one of the nucleases, nuclease Le1, has been analyzed by both protein chemistry and gene cloning [Biosci. Biotechnol. Biochem. 64, 948-957 (2000)]. In this study the amino acid sequence of nuclease Le3 was analyzed by protein chemistry and gene cloning. Nuclease Le3 is a glycoprotein that contains 280 amino acid residues, and the molecular mass of the protein moiety of nuclease Le3 is 31,045. The nucleotide sequence of the cDNA and genomic DNA encoding nuclease Le3 revealed the presence of an 18-residue putative signal peptide. Nuclease Le3 contains 170, 108, and 98 amino acid residues that are identical to residues of nuclease Le1, nuclease P1, and nuclease S, respectively. The amino acid residues involved in coordination with Zn2+ atoms in nuclease P1 are all conserved in nuclease Le3. Nuclease Le3 contains 9 half-cystine residues, and 7 of them are located in the same positions as in nuclease Le1.