The Neisseria gonorrhoeae Obg protein is an essential ribosome-associated GTPase and a potential drug target.

Background: Neisseria gonorrhoeae (GC) is a Gram-negative pathogen that most commonly infects mucosal surfaces, causing sexually transmitted urethritis in men and endocervicitis in women. Serious complications associated with these infections are frequent and include pelvic inflammatory disease, ectopic pregnancy, and infertility. The incidence of gonorrhea cases remains high globally while antibiotic treatment options, the sole counter measures against gonorrhea, are declining due to the remarkable ability of GC to acquire resistance. Evaluating of potential drug targets is essential to provide opportunities for developing antimicrobials with new mechanisms of action. We propose the GC Obg protein, belonging to the Obg/CgtA GTPase subfamily, as a potential target for the development of therapeutic interventions against gonorrhea, and in this study perform its initial functional and biochemical characterization.

Results: We report that NGO1990 encodes Obg protein, which is an essential factor for GC viability, associates predominantly with the large 50S ribosomal subunit, and is stably expressed under conditions relevant to infection of the human host. The anti-Obg antisera cross-reacts with a panel of contemporary GC clinical isolates, demonstrating the ubiquitous nature of Obg. The cellular levels of Obg reach a maximum in the early logarithmic phase and remain constant throughout bacterial growth. The in vitro binding and hydrolysis of the fluorescent guanine nucleotide analogs mant-GTP and mant-GDP by recombinant wild type and T192AT193A mutated variants of Obg are also assessed.

Conclusions: Characterization of the GC Obg at the molecular and functional levels presented herein may facilitate the future targeting of this protein with small molecule inhibitors and the evaluation of identified lead compounds for bactericidal activity against GC and other drug-resistant bacteria.