Thiamine metabolism genes are regulated in numerous bacteria by a riboswitch class that binds the coenzyme thiamine pyrophosphate (TPP). We demonstrate that the antimicrobial action of the thiamine analog pyrithiamine (PT) is mediated by interaction with TPP riboswitches in bacteria and fungi. For example, pyrithiamine pyrophosphate (PTPP) binds the TPP riboswitch controlling the tenA operon in Bacillus subtilis. Expression of a TPP riboswitch-regulated reporter gene is reduced in transgenic B. subtilis or Escherichia coli when grown in the presence of thiamine or PT, while mutant riboswitches in these organisms are unresponsive to these ligands. Bacteria selected for PT resistance bear specific mutations that disrupt ligand binding to TPP riboswitches and derepress certain TPP metabolic genes. Our findings demonstrate that riboswitches can serve as antimicrobial drug targets and expand our understanding of thiamine metabolism in bacteria.
Bibliographical noteFunding Information:
R.R.B. is cofounder of a biotechnology company, BioRelix, that is pursuing licensing of intellectual property related to riboswitches. We thank Dr. Jinsoo Lim for purification of PTPP. This work was supported by grants from the Defense Advanced Research Projects Agency, National Institutes of Health, and the David and Lucile Packard Foundation. We thank members of the Breaker laboratory for helpful discussions.