Solution structure of subunit γ (γ_1-204) of the Mycobacterium tuberculosis F-ATP synthase and the unique loop of γ_165-178, representing a novel TB drug target

Tuberculosis, caused by the strain Mycobacterium tuberculosis, is in focus of interest due to the emergence of multi- and extensive drug-resistant TB strains. The F₁F_O ATP synthase is one of the essential enzymes in energy requirement of both proliferating aerobic and hypoxic dormant stage of mycobacterium life cycle, and therefore a potential TB drug target. Subunit γ of F-ATP synthases plays an important role in coupling and catalysis via conformational transitions of its N- and C-termini as well as the bottom segment of the globular domain of γ, which is in close proximity to the rotating and ion-pumping c-ring. Here we describe the first production, purification and low resolution solution structure of subunit γ (γ_1-204, Mtγ_1-204) of the M. tuberculosis F-ATP synthase. Mtγ_1-204 is a pear-like shaped protein with a molecular weight of 23 ± 2 kDa. Protein sequence analysis of Mtγ revealed differences in the amino acid composition to γ subunits from other sources, in particular the presence of a unique stretch of 13 amino acid residues (Mtγ_165-178). NMR studies showed that Mtγ_165-178 forms a loop of polar residues. Mtγ _165-178 has been aligned at the bottom of the globular domain of the Escherichia coli subunit γ, being in close vicinity to the polar residues R41, Q42, E44 and Q46 (M. tuberculosis nomenclature) of the c-ring. The putative role(s) of Mtγ_165-178 in coupling and as a potential drug target are discussed.