Methylation in hangtaimycin biosynthesis and its antibacterial activities

About two-thirds of small molecule drugs contain methyl group and it plays a very important role in the drug development. So, methyltransferases catalyzing the methylation have always attracted great attention. Hangtaimycin (HTM) is a potent hepatoprotective agent. Previous study showed that its biosynthetic gene cluster contained three methyltransferase domains, but their characteristics in HTM biosynthetic pathway has not been revealed. In this study, we clarified multi-methylations in HTM biosynthesis in vivo. It showed that the two S-adenosylmethionine-dependent methyltransferases (SAM-MTs) of HtmA2(-module 6)-MT domain and HtmB2(-module 18)-MT domain are responsible for the installation of methyl group at C-45 and N-12, respectively, whereas the FK506 methyltransferase (FKMT) type O-methyltransferase of HtmB1(-module 16)-MT domain take care of the methylation at O-21 of HTM. We also reported the antibacterial activities of HTM in this study, and found that it showed activities against M. luteus, B. thuringiensis and A. baumannii with MIC of 4 μg/mL, 4 μg/mL, and 64 μg/mL, respectively.