subtilis SigB in response to physical stress. This activation occurs via Obg’s

physical Z-VAD-FMK nmr interaction with upstream Rsb regulators of SigB [16]. Further, the GTP-binding pocket of crystallized Obg of B. subtilis contains guanosine 5′ diphosphate, 3′ phosphate (ppGpp) [16]. ppGpp is a guanosine nucleotide known as an alarmone in bacteria. Alarmones are produced in response to amino acid starvation, and they act as signaling intermediates to slow cell growth or to initiate stress-induced differentiation pathways, including sporulation. In bacteria, the synthesis of ppGpp is performed by two enzymes, called RelA and SpoT [17–19]. In E. coli, SpoT is one of the proteins known to interact with Obg [20]. In V. cholerae, depletion of the Obg homologue CgtA results in a global gene expression pattern reflecting the low-nutrient stress reaction called the “”stringent”" response [21]. In V. cholerae, CgtA interacts with SpoT, and this interaction decreases SpoT

activity leading to the repression of the stringent response [21]. Another interesting example of Obg’s association with stress comes from the pathogen Legionella pneumophila, where its expression is elevated during intracellular survival [22]. Recent studies indicate that Obg associates with ribosomes of bacteria and interacts with ribosomal proteins. In B. subtilis, Obg coelutes with ribosomal proteins and interacts specifically with the ribosomal protein L13, a component of the CYTH4 50 S ribosomal subunit [23]. The Obg orthologues of C. crescentus [24],

V. harveyi [25] and E. coli [20, 26] also cofractionate with the 50 S ribosomal subunit. Finally, bacterial Obg selleck screening library has also been implicated in chromosomal partitioning [11] and replication regulation [27]. Mycobacterium tuberculosis is an intracellular pathogen and causative agent of tuberculosis in humans. The recent emergence of multidrug (MDR-TB) and extremely drug resistant (XTR-TB) M. tuberculosis strains now poses serious threats to people in the developing world [27], and combating the disease requires the development of new anti-tuberculosis drugs. However, design and development of new drugs for TB largely depends upon the identification and characterization of novel drug targets in M. tuberculosis. The fact that Obg is an essential protein for growth in bacteria, including M. tuberculosis [28], and its association with ribosomes makes it a potential target for future antimicrobials [29, 30]. Thus, this study was undertaken to understand the basic properties of Obg of M. tuberculosis. Results and Discussion Overexpressed M. tuberculosis Obg binds to, and hydrolyzes, GTP A single copy of the gene coding for Obg (Rv2440c) is present in the genome of M. tuberculosis, between the genes proB (Rv2439c) and rpmA (Rv2441c). The deduced amino acid sequence of the M. tuberculosis Obg protein shows significant similarities with the Obg proteins of B. subtilis, S. coelicolor and other bacterial species (Additional file 1).