A systematic assessment of mycobacterial F1 -ATPase subunit ε's role in latent ATPase hydrolysis.

In contrast to most bacteria, the mycobacterial F1 FO -ATP synthase (α3 :ß3 :γ:δ:ε:a:b:b':c9 ) does not perform ATP hydrolysis-driven proton translocation. Although subunits α, γ and ε of the catalytic F1 -ATPase component α3 :ß3 :γ:ε have all been implicated in the suppression of the enzyme's ATPase activity, the mechanism remains poorly defined. Here, we brought the central stalk subunit ε into focus by generating the recombinant Mycobacterium smegmatis F1 -ATPase (MsF1 -ATPase), whose 3D low-resolution structure is presented, and its ε-free form MsF1 αßγ, which showed an eightfold ATP hydrolysis increase and provided a defined system to systematically study the segments of mycobacterial ε's suppression of ATPase activity. Deletion of four amino acids at ε's N terminus, mutant MsF1 αßγεΔ2-5 , revealed similar ATP hydrolysis as MsF1 αßγ. Together with biochemical and NMR solution studies of a single, double, triple and quadruple N-terminal ε-mutants, the importance of the first N-terminal residues of mycobacterial ε in structure stability and latency is described. Engineering ε's C-terminal mutant MsF1 αßγεΔ121 and MsF1 αßγεΔ103-121 with deletion of the C-terminal residue D121 and the two C-terminal ɑ-helices, respectively, revealed the requirement of the very C terminus for communication with the catalytic α3 ß3 -headpiece and its function in ATP hydrolysis inhibition. Finally, we applied the tools developed during the study for an in silico screen to identify a novel subunit ε-targeting F-ATP synthase inhibitor.

Disrupting coupling within mycobacterial F-ATP synthases subunit ε causes dysregulated energy production and cell wall biosynthesis.

The dynamic interaction of the N- and C-terminal domains of mycobacterial F-ATP synthase subunit ε is proposed to contribute to efficient coupling of H+-translocation and ATP synthesis. Here, we investigate crosstalk between both subunit ε domains by introducing chromosomal atpC missense mutations in the C-terminal helix 2 of ε predicted to disrupt inter domain and subunit ε-α crosstalk and therefore coupling. The ε mutant εR105A,R111A,R113A,R115A (ε4A) showed decreased intracellular ATP, slower growth rates and lower molar growth yields on non-fermentable carbon sources. Cellular respiration and metabolism were all accelerated in the mutant strain indicative of dysregulated oxidative phosphorylation. The ε4A mutant exhibited an altered colony morphology and was hypersusceptible to cell wall-acting antimicrobials suggesting defective cell wall biosynthesis. In silico screening identified a novel mycobacterial F-ATP synthase inhibitor disrupting ε's coupling activity demonstrating the potential to advance this regulation as a new area for mycobacterial F-ATP synthase inhibitor development.