Isolation, Structure Elucidation, and Biosynthesis of a Cysteate-Containing Nonribosomal Peptide in Streptomyces lincolnensis.

The species Streptomyces lincolnensis is known as a producer of lincomycin A, a clinically important lincosamide antibiotic with activity against Gram-positive bacteria. Here, we report that S. lincolnensis produces a new cysteate-containing lactone product, cysteoamide (1), which arises from nonribosomal peptide synthetase-programmed sequential assembly of the monomers phenylacetic acid, valine, cysteate, threonine, β-hydroxyleucine, and β-alanine and subsequent intramolecular cyclization to form a lactone ring. The structure of 1 was determined by combined analysis of NMR and MS spectra, while the amino acid absolute configurations in 1 were assigned by Marfey's analysis following acid hydrolysis. The biosynthetic gene cluster of 1 was defined in the genome of S. lincolnensis by bioinformatics analysis and in vivo genetic study. In addition, in vitro assay revealed that OrfA, a pyridoxal 5'-phosphate-dependent protein, is responsible for the formation of the unusual cysteate unit. Cysteate-containing nonribosomal peptides appear to be widely present in various Streptomyces strains, and this study generates interest in their intrinsic functions that remain poorly understood.