The transpeptidase PbpA and non-canonical transglycosylase RodA of Mycobacterium tuberculosis play important roles in regulating bacterial cell lengths

Abstract

The cell wall of Mycobacterium tuberculosis (Mtb) is a complex structure that protects the pathogen in hostile environments. Peptidoglycan (PG), which helps determine the morphology of the cell envelope, undergoes substantial remodeling under stress. This meshwork of linear chains of sugars, crosslinked through attached peptides, is generated through the sequential action of enzymes termed transglycosylases and transpeptidases. The Mtb genome encodes two classical transglycosylases and four transpeptidases, the functions of which are not fully elucidated. Here, we present work on the yet uncharacterized transpeptidase PbpA and a non-classical transglycosylase RodA. We elucidate their roles in regulating in vitro growth and in vivo survival of pathogenic mycobacteria. We find that RodA and PbpA are required for regulating cell length, but do not affect mycobacterial growth. Biochemical analyses show PbpA to be a classical transpeptidase, while RodA is identified to be a member of an emerging class of non-canonical transglycosylases. Phosphorylation of RodA at T463 modulates its biological function. In a guinea pig infection model, RodA and PbpA are found to be required for both, bacterial survival as well as formation of granuloma structures, thus underscoring the importance of these proteins in mediating mycobacterial virulence in the host. Our results emphasize the fact that while redundant enzymes likely compensate for the absence of RodA or PbpA during in vitro growth, the two proteins play critical roles for the survival of the pathogen inside its host.