Discovery and biosynthesis of the redox cofactor mycofactocin

Mycobacterium tuberculosis, the etiological agent of tuberculosis (TB), can survive as an intracellular pathogen residing in a granulomatous lesion in the lungs. Current TB treatments comprise a long course of several antibiotics with various side effects. Incomplete treatment is leading to antibiotic resistance, a growing threat worldwide. It has been recognized that both antibiotic inactivation and intracellular survival is often mediated by organic cofactors. Furthermore, novel therapeutic compounds in use are prodrugs that require cofactors for in vivo conversion into an active pharmaceutical entity. Mycobacterial cofactors are an up-and-coming field of research for developing novel therapeutic compounds. As such, novel cofactors offer an exciting opportunity to discover novel aspects in the pathogen's physiology and pathology as well as inspiring novel avenues for TB management. Mycofactocin (MFT) is a novel redox cofactor, part of the family of natural products termed ribosomally produced and post-translationally modified peptides and a universal genomic feature of the Mycobacterium genus. Its discovery was spurred from the bioinformatic observation of a gene locus in the vicinity of a radical SAM maturase, containing a small peptide precursor, a chaperone, a peptidase, and a glycosyltransferase, alongside putative MFT-dependent redox enzymes and other genes encoding proteins of unknown function. In-vitro investigation of the biosynthesis pathway showed the formation of the redox-active precursor premycofactocin. In addition, in-vivo studies with the model organism Mycolicibacterium smegmatis have associated MFT to the metabolism of primary alcohols for assimilation as a carbon source. Critical questions remained, such as whether the in vitro biosynthetic model is valid in vivo, the function of the putative glycosyltransferase, the enzymology of MFT-dependent oxidoreductases and dehydrogenases, and the role of MFT in mycobacterial pathogenesis.