3.A.2.1.1
H⁺-translocating F-type ATPase. The loop-regions in subunits a and c that are implicated in H⁺ transport likely interact in a single structural domain which then functions in gating H⁺ release to the cytoplasm (Steed et al. 2014). Three different states that relate to rotation of the enzyme have been observed, with the central stalk's epsilon subunit in an extended autoinhibitory conformation in all three states (Sobti et al. 2016). The Fo motor consists of seven transmembrane helices and a decameric c-ring, and invaginations on either side of the membrane indicate the entry and exit channels for protons. The proton translocating subunit contains near parallel helices inclined by ~30 degrees to the membrane, a feature corresponding to rotary ATPases. This rotary ATPase subtype, the peripheral stalk, is resolved over the entire length of the complex, revealing the F1 attachment points and a coiled-coil that bifurcates toward the membrane with its helices separating to embrace subunit a from two sides (Sobti et al. 2016). Reversible beta/epsilon (stator/rotor) interactions may block rotation and thereby inhibit catalysis (Bulygin et al. 2004). Current views on unidirectional catalysis by the F₁·F_o ATP synthase/ATPase have been reviewed (Zharova et al. 2023). Hypermucoviscosity is a hallmark of hypervirulent Klebsiella pneumoniae, and OmpR regulates its energy status, via the F-type ATPase of this organism; this influences hypermucoviscosity (Wang et al. 2023).