N-Deacetylation in Lincosamide Biosynthesis Is Catalyzed by a TldD/PmbA Family Protein.

Lincosamides are clinically important antibiotics originally produced as microbial specialized metabolites. The complex biosynthesis of lincosamides is coupled to the metabolism of mycothiol as a sulfur donor. Here, we elucidated the N-deacetylation of the mycothiol-derived N-acetyl-l-cysteine residue of a lincosamide intermediate, which is comprised of an amino acid and an aminooctose connected via an amide bond. We purified this intermediate from the culture broth of a deletion mutant strain and tested it as a substrate of recombinant lincosamide biosynthetic proteins in the in vitro assays that were monitored via liquid chromatography-mass spectrometry. Our findings showed that the N-deacetylation reaction is catalyzed by CcbIH/CcbQ or LmbIH/LmbQ proteins in celesticetin and lincomycin biosynthesis, respectively. These are the first N-deacetylases from the TldD/PmbA protein family, from which otherwise only several proteases and peptidases were functionally characterized. Furthermore, we present a sequence similarity network of TldD/PmbA proteins, which suggests that the lincosamide N-deacetylases are unique among these widely distributed proteins.