Uncovering a Glycosyltransferase Provides Insights into the Glycosylation Step during Macrolactin and Bacillaene Biosynthesis

Abstract

Macrolactins (MLNs) have unique structural patterns containing a 24-membered ring lactone and diverse bioactivities. The MLN skeleton is biosynthesized via a trans-acyl transferase (AT) type I polyketide synthase (PKS) pathway, but the tailoring steps are still unknown. Herein, we report the identification of a glycosyltransferase (GT) gene bmmGT1, which is located at different locus from the MLN gene cluster in the genome of marine-derived Bacillus marinus B-9987, and its functional characterization as an MLN GT, thus affording five novel MLNs analogues. Surprisingly, this GT is also capable of catalyzing the glycosylation of bacillaenes (BAEs), which are the prototypes of trans-AT polyketides, thus suggesting broad substrate flexibility. These results provide the first significant insights into the glycosylation step in MLN and BAE biosynthetic pathways.

Genome‐wide identification and characterization of macrolide glycosyltransferases from a marine‐derived Bacillus strain and their phylogenetic distribution

“…In our previous study, we identified and characterized the GT gene bmmGT1 , which is involved in glycosylation of both MLNs and BAEs (Qin et al ., ). Interestingly, bmmGT1 is not a unique GT gene in the MLN‐producing strains, but instead it is also present in some other Bacillus genomes.…”

“…, panel ii and iii). The above results indicated that bmmGT2 and bmmGT3 are not essential for the biosynthesis of glycosylated MLNs or BAEs, consistent with our previous result that bmmGT1 is responsible for the glycosylation steps of MLNs and BAEs in vivo (Qin et al ., ). In addition, the fermentation broth of ΔbmmGT1 mutant was further carefully checked by HPLC‐MS, in which we observed trace amount of glycosylated MLN ( 1b ) and BAE ( 4b ) (Supporting Information Fig.…”

“…In addition, compounds 1e and 1f appeared when using 10 µM of BmmGT2 (panel iv), suggesting successive glycosylation may happen at high concentration of BmmGT2. With the presence of hydroxyl groups at C‐13 and C‐15 of 1a , we proposed that glycosylation happened at these two positions as well, indicating different regioselectivity of BmmGT2 and BmmGT3 compared with that of BmmGT1, which prefers to catalyze glycosylation at 7‐OH (Qin et al ., ).…”

“…Given BmmGT1 is involved in glycosylation of both MLNs and BAEs (Qin et al ., ), BmmGT2 and BmmGT3 were tested with 4a as well. The results showed that, just like BmmGT1, BmmGT2 was able to catalyze glycosylation of 4a to generate 4b (retention time at 13.880 min) (Fig.…”

“…The N‐terminal domain provides the acceptor‐binding site and the C‐terminal domain contains the NDP‐sugar donor‐binding site; catalysis occurs at the interface of these domains (Chang et al ., ). Most bacterial natural‐product GTs that have been functionally characterized are from Actinomyces strains (Erb et al ., ; Gantt et al ., ); conversely, our understanding towards Bacillus natural‐product GTs is so far very limited (Ko et al ., ; Ahn et al ., ; Gurung et al ., ; Pandey et al ., ; Qin et al ., ).…”