Protein protein Interactions of NarL with NarG, SsrB, and FNR Proteins in Salmonella Typhimurium: A Comparative Analysis.

Salmonella Typhimurium (STM) is the leading cause of gastroenteritis in humans and animals worldwide. Nitrate anaerobic regulator L (NarL), a global transcription factor of STM, interacts with different binding partners and thereby influences bacterial colonization and virulence under anaerobic conditions. The present study was conducted with the objective of elucidating the interactions of the NarL protein with its binding partners, such as nitrate reductase G (NarG), Secretion system regulator transcriptional activator (SsrB), and Fumarate and nitrate regulator (Fnr). Therefore, NarL, NarG, SsrB, and FNR proteins were first expressed in the prokaryotic system and the binding of NarL with NarG, SsrB, and FNR was evaluated through microtitre plate assay, dot blot, blot overlay assay, gold nanoparticle based protein binding assay, and circular dichroism spectroscopy. The NarL-NarG binding interaction was found to be significantly stronger (P < 0.05) than NarL-SsrB, followed by the NarL-FNR interaction. Binding interactions were further validated with isothermal titration calorimetry, and it was observed that the NarL-NarG interaction was exothermic with a ΔG of -16.4 kcal/mol, while the binding of NarL-SsrB was endothermic with a ΔG of 7.6 kcal/mol. However, FNR protein did not show any gain or release of free energy during interaction with NarL protein. Further, the molecular docking showed a higher binding energy score between NarL-NarG complex than NarL-SsrB and NarL-FNR protein complex. These results provide basic information that would facilitate the development of novel therapeutics against STM by targeting these specific interactions.