Structure and subunit arrangement of Mycobacterial F1FO ATP synthase and novel features of the unique mycobacterial subunit δ.

• First purification protocol of an intact mycobacterial F-ATP synthase. • First low resolution structure of an entire mycobacterial F-ATP synthase. • Purification of the fused mycobacterial b -δ 24-446 construct. • The novel 111-residues domain of mycobacterial subunit δ. • The potential of mycobacterial subunit δ as a drug target. In contrast to other prokaryotes, the Mycobacterial F 1 F O ATP synthase (α 3 :β 3 :γ:δ:ε: a : b : b' : c 9) is essential for growth. The mycobacterial enzyme is also unique as a result of its 111 amino acids extended δ subunit, whose gene is fused to the peripheral stalk subunit b. Recently, the crystallographic structures of the mycobacterial α 3 :β 3 :γ:ε-domain and c subunit ring were resolved. Here, we report the first purification protocol of the intact M. smegmatis F 1 F O ATP synthase including the F 1 -domain, the entire membrane-embedded F O sector, and the stator subunits b' and the fused b -δ. This enzyme purification enabled the determination of the first projected 2D- and 3D structure of the intact M. smegmatis F 1 F O ATP synthase by electron microscopy (EM) and single particle analysis. Expression and purification of the fused mycobacterial b -δ 24-446 construct, excluding the membrane-embedded N-terminal amino acids, provided insight into its secondary structure. By combining these data with homology and ab-initio modeling techniques, a model of the mycobacterial peripheral stalk subunits b -δ and b ' was generated. Superposition of the 3D M. smegmatis F-ATP synthase EM-structure, the α 3 :β 3 :γ:ε and c -ring, and the derived structural models of the peripheral stalk enabled a clear assignment of all F-ATP synthase subunits, in particular with respect to the unique mycobacterial peripheral stalk subunit b' and the elongated δ fused with subunit b. The arrangement of δ relative to the N-termini of the catalytic α 3 β 3 -headpiece and its potential as a drug target are discussed. [ABSTRACT FROM AUTHOR]