Expanding tryptophan-containing cyclodipeptide synthase spectrum by identification of nine members from Streptomyces strains

Cyclodipeptide synthases (CDPSs) comprise normally 200-300 amino acid residues and are mainly found in bacteria. They hijack aminoacyl-tRNAs from the ribosomal machinery for cyclodipeptide formation. In this study, nine new CDPS genes from eight Streptomyces strains were cloned into pET28a vector and expressed in Escherichia coli. Structural elucidation of the isolated products led to the identification of one cyclo-l-Trp-l-Leu, two cyclo-l-Trp-l-Pro, and three cyclo-l-Trp-l-Trp synthases. Other three CDPSs produce cyclo-l-Trp-l-Ala or cyclo-l-Trp-l-Tyr as the major cyclodipeptide. Total product yields of 46 to 211 mg/L E. coli culture were obtained. Our findings represent rare examples of CDPS family derived from actinobacteria that form various tryptophan-containing cyclodipeptides. Furthermore, this study highlights the potential of the microbial machinery for tryptophan-containing cyclodipeptide biosynthesis and provides valid experimental basis for further combination of these CDPS genes with other modification genes in synthetic biology.