Identification of the Enzymes Mediating the Maturation of the Seryl-tRNA Synthetase Inhibitor SB-217452 during the Biosynthesis of Albomycins.

Albomycin δ2 is a sulfur-containing sideromycin natural product that shows potent antibacterial activity against clinically important pathogens. The l-serine-thioheptose dipeptide partial structure, known as SB-217452, has been found to be the active seryl-tRNA synthetase inhibitor component of albomycin δ2 . Herein, it is demonstrated that AbmF catalyzes condensation between the 6'-amino-4'-thionucleoside with the d-ribo configuration and seryl-adenylate supplied by the serine adenylation activity of AbmK. Formation of the dipeptide is followed by C3'-epimerization to produce SB-217452 with the d-xylo configuration, which is catalyzed by the radical S-adenosyl-l-methionine enzyme AbmJ. Gene deletion suggests that AbmC is involved in peptide assembly linking SB-217452 with the siderophore moiety. This study establishes how the albomycin biosynthetic machinery generates its antimicrobial component SB-217452.

Characterization of the aurantimycin biosynthetic gene cluster and enhancing its production by manipulating two pathway-specific activators in Streptomyces aurantiacus JA 4570.

BACKGROUND: Aurantimycin (ATM), produced by Streptomyces aurantiacus JA 4570, is a potent antimicrobial and antitumor antibiotic. Although the chemical structure of ATM is highly distinctive and features a cyclohexadepsipeptide scaffold attached with a C14 acyl side chain, little is known about its biosynthetic pathway and regulatory mechanism. RESULTS: In this work, we report the identification and characterization of the ATM biosynthetic gene cluster from S. aurantiacus JA 4570. Targeted inactivation of artG, coding for a NRPS enzyme, completely abolished ATM production, thereof demonstrating the target gene cluster (art) is responsible for ATM biosynthesis. Moreover, four NRPS adenylation (A) domains including a freestanding enzyme ArtC have been characterized in vitro, whose substrate specificities are consistent with in silico analysis. Further genetic analysis of the two regulatory genes artB and artX unambiguously suggested both of them play positive roles in ATM biosynthesis, and ATM-A production was thus rationally enhanced to about 2.5 fold via tandem overexpression of artB and artX in S. aurantiacus JA 4570. CONCLUSIONS: These results will provide the basis for the understanding of precise mechanisms for ATM biosynthesis, and open the way for both rational construction of high-production ATM producer and orient-directed generation of designer ATM derivatives via synthetic biology strategies.