Beta-alanyl peptide synthesis by Streptomyces S9 aminopeptidase.

Synthesis of beta-alanine (beta-Ala) containing dipeptide using S9 aminopeptidase from Streptomyces thermocyaneoviolaceus NBRC14271 (S9AP-St) was demonstrated with beta-Ala-benzyl ester (-OBzl) and various L-aminoacyl derivatives. For synthesis of beta-Ala-containing dipeptide, beta-Ala-OBzl was used preferentially as the acyl donor for S9AP-St, producing synthesized dipeptides having beta-Ala-Xaa structure. In contrast, engineering of S9AP-St into "transaminopeptidase" by substitution of catalytic Ser with Cys--designated as aminolysin-S--produced only dipeptides having Xaa-beta-Ala structure. Investigation of the specificity of S9AP-St toward acyl acceptors showed that S9AP has a broad substrate specificity toward various aminoacyl derivatives. Furthermore, S9AP-St produced carnosine methyl ester (-OMe) with a conversion ratio of beta-Ala-OBzl to carnosine-OMe that was greater than 30%.