β-Alanyl peptide synthesis by Streptomyces S9 aminopeptidase

Synthesis of β-alanine (β-Ala) containing dipeptide using S9 aminopeptidase from Streptomyces thermocyaneoviolaceus NBRC14271 (S9AP-St) was demonstrated with β-Ala-benzyl ester (-OBzl) and various l-aminoacyl derivatives. For synthesis of β-Ala-containing dipeptide, β-Ala-OBzl was used preferentially as the acyl donor for S9AP-St, producing synthesized dipeptides having β-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-β-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 β-Ala-OBzl to carnosine-OMe that was greater than 30%.