A product of RpfB and RipA joint enzymatic action promotes the resuscitation of dormant mycobacteria

Resuscitation-promoting factor proteins (Rpfs) are known to participate in reactivating the dormant forms of actinobacteria. Structural analysis of the Rpf catalytic domain demonstrates its similarity to lysozyme and to lytic transglycosylases - the groups of enzymes that cleave the -1,4-glycosidic bond between N-acetylmuramic acid (MurNAc) and GlcNAc, and concomitantly form a 1,6-anhydro ring at the MurNAc residue. Analysis of the products formed from mycobacterial peptidoglycan hydrolysis reactions containing a mixture of RpfB and resuscitation-promoting factor interacting protein (RipA) allowed us to identify the suggested product of their action - N-acetylglucosaminyl-(14)-N-glycolyl-1,6-anhydromuramyl-l-alanyl-d-isoglutamate. To identify the role of this resulting product in resuscitation, we used a synthetic 1,6-anhydrodisaccharide-dipeptide, and tested its ability to stimulate resuscitation by using the dormant Mycobacteriumsmegmatis model. It was found that the disaccharide-dipeptide was the minimal structure capable of resuscitating the dormant mycobacterial cells over the concentration range of 9-100ngmL(-1). The current study therefore provides the first insights into the molecular mechanism of resuscitation from dormancy involving a product of RpfB/RipA-mediated peptidoglycan cleavage.