2.8.7. Structural Classification of the Selected VDA Proteins

*Rv0554* is an integral part of the menaquinone regulatory operon in Mycobacterium. Menaquinone is a crucial factor in the mycobacterial electron transport chain [45]. *Rv1477* is a mycobacterial resuscitation promoting factor interacting protein (*RipA*) and participates in the cleavage of peptide cross linkages between peptidoglycans similar to other cleavage enzymes, such as *OwlT* and *Spr* in *B. subtilis* and *E. coli*, respectively [46]. *Rv1495* is designated as *mazEF*, which is a subcomponent of the type II toxin–antitoxin system in mycobacteria [47]. *Rv1566c* (*RipD*) is a predicted peptidoglycan specific peptidase of the NlpC/p60 family. The unusual peptide linkages of *Mycobacterium* i.e., L-D and D-D and other isopeptide linkages makes the peptide resilient to cleavage by mycobacterial peptidases [48]. *Rv1636* is a universal stress protein (USP) in *M. tuberculosis*. In *M. tuberculosis*, it is classified into class I USP, based on the presence of only a single conserved domain of USP, which is of similar size to *UspA*. CAMP is bound to *Rv1636*, which regulates the signaling associated with the cAMP molecule [49]. *Rv2010* of *M. tuberculosis* codes for *VapC*-15 toxin. These proteins belong to the PIN domain family proteins and contain ribonuclease activity [50]. *Rv2549c* is designated as *VapC20* of *M. tuberculosis* and along *VapB*, it forms *VapBC* toxin antitoxin complex [51]. *Rv2623* is a universal stress protein of *M. tuberculosis*, that helps mycobacteria in different stress conditions and is also important for mycobacterial growth and persistence [52]. *Rv2757c* of *M. tuberculosis* codes for *VapC*-21 toxin. These proteins also belong to the PIN domain family proteins and contain ribonuclease activity [53]. *Rv2801c* encodes for the *MazF*-mt1 protein of *M. tuberculosis*. *MazF* is a known component of the *MazEF* toxin–antitoxin system in many prokaryotic cells [54].
