Mycobacterium tuberculosis ArfA Rv0899

Function

Protein Rv0899 from Mycobacterium tuberculosis [1] belongs to the OmpA (outer membrane protein A) family of outer membrane proteins.The deletion of this gene impairs the uptake of some water-soluble substances, such as serine, glucose, and glycerol.Using NMR chemical shift perturbation and isothermal calorimetric titration assays, Rv0899 was able to interact with Zn(2+) ions, which may indicate a role for Rv0899 in the process of Zn(2+) acquisition. ^[1] Mycobacterium tuberculosis ArfA (Rv0899) is a membrane protein encoded by an ammonia release facilator operon that is necessary for rapid ammonia secretion, pH neutralization and adaptation to acidic environments in vitro. Its C-terminal domain (C domain) shares significant sequence homology with the OmpA-like family of peptidoglycan-binding domains, suggesting that its physiological function in acid stress protection may be related to its interaction with the mycobacterial cell wall. ArfA is identified as a peptidoglycan-binding protein. It exhibits pH-dependent conformational dynamics (with significant heterogeneity at neutral pH and a more ordered structure at acidic pH), which could be related to its acid stress response. The C domain associates tightly with polymeric peptidoglycan isolated from M. tuberculosis and also associates with a soluble peptide intermediate of peptidoglycan biosynthesis. This enabled us to characterize the peptidoglycan binding site where five highly conserved ArfA residues, including two key arginines, establish the specificity for diaminopimelate- but not Lys-type peptidoglycan. Its functions in acid stress protection and peptidoglycan binding suggest a link between the acid stress response and the physicochemical properties of the mycobacterial cell wall.^[2] Chemical analysis of low-pH culture filtrates showed that the proteins encoded by the ompATb operon are involved in generating a rapid ammonia burst (Ammonia release facilator operon is necessary for rapid ammonia secretion, pH neutralization and adaptation to acidic environments in vitro , which neutralized medium pH Addition of ammonia accelerated growth of the ompATb operon mutant demonstrating that ammonia secretion is indeed a mechanism by which M. tuberculosis neutralizes acidic environments. Infection experiments revealed that the ompATb operon was not required for full virulence in mice suggesting that M. tuberculosis has multiple mechanisms of resisting phagosomal acidification. The ompATb operon is necessary for rapid ammonia secretion and adaptation of M. tuberculosis to acidic environments in vitro but not in mice. ^[3]

Disease

Rv0899 has been proposed to act as an outer membrane porin and to contribute to the bacterium's adaptation to the acidic environment of the phagosome[2] during infection. The gene is restricted to pathogenic mycobacteria and, thus, is an attractive candidate for the development of anti-tuberculosis chemotherapy. ^[4] Probably plays a role in ammonia secretion that neutralizes the medium at pH 5.5,and preceded exponential growth of M. tuberculosis, although it does not play a direct role in ammonia transport.[ARFA_MYCTU]. Its functions in acid stress protection and peptidoglycan binding suggest a link between the acid stress response and the physicochemical properties of the mycobacterial cell wall.^[5]

Relevance

Structural highlights