Proteomic and epi/proteomic response of Mycobacterium tuberculosis to nitric oxide stress

Reactive nitrogen species (RNS) are the major antimicrobial molecules secreted by host cells to tackle Mycobacterium tuberculosis (Mtb) infection. Mtb respond and adapt to adverse environmental stressors by changes in gene expression, ensuring their survival. This adaptation process is mediated by a combination of transcriptional regulatory networks that result in altered gene expression and enzyme (protein) activities. Previous studies emphasized primarily on transcriptomic response of Mtb to different environmental stresses, including RNS. In this study, the proteomic response of Mtb to sublethal doses of RNS stress after 30 minutes, 2 hours, 6 hours and 20 hours was explored. We used liquid chromatography coupled with electrospray ionization mass spectrometry (LC-MS/MS) to elucidate the proteomic response of Mtb to RNS. Quantitative proteomic analysis revealed identification of 2911 proteins and 6460 acylations in Mtb. A total of 581 unique proteins were found to be affected by RNS at different time points. Multiple-sample test revealed 297 differentially regulated proteins across the four time points. Furthermore, multiple-sample test identified 127 differentially acylated sites on 94 proteins. Marked changes in proteomic response was observed at later time points, most of which were compensatory responses involved in SOS response, iron homeostasis, energy metabolism and other stress responses. This study provides an improved understanding of the dynamic proteomic response of Mtb to RNS and identification of key molecular switches, which is the basis of controlling bacterial growth in different environmental setting.