The proteomic response of mycobacterium smegmatis to anti-tuberculosis drugs suggests targeted pathways

Mycobacterium smegmatis is a fast-growing model mycobacterial system that shares many features with the pathogenic Mycobacterium tuberculosis while allowing practical proteomics analysis. With the use of shotgun-style mass spectrometry, we provide a large-scale analysis of the M. smegmatis proteomic response to the anti-tuberculosis (TB) drugs isoniazid, ethambutol, and 5-chloropyrazinamide and elucidate the drugs' systematic effects on mycobacterial proteins. A total of 2550 proteins were identified with ∼5% false-positive identification rate across 60 experiments, representing ∼40% of the M. smegmatis proteome (∼6500 proteins). Protein differential expression levels were estimated from the shotgun proteomics data, and 485 proteins showing altered expression levels in response to drugs were identified at a 99% confidence level. Proteomic comparison of anti-TB drug responses shows that translation, cell cycle control, and energy production are down-regulated in all three drug treatments. In contrast, systems related to the drugs' targets, such as lipid, amino acid, and nucleotide metabolism, show specific protein expression changes associated with a particular drug treatment. We identify proteins involved in target pathways for the three drugs and infer putative targets for 5-chloropyrazinamide.