Session: Current Topics in Biological Chemistry:

ATP synthase is a membrane protein complex that synthesizes adenosine triphosphate (ATP), an integral molecule that provides energy to all forms of life. The complex is comprised of two rotary motors, the soluble F₁ sector and the membrane embedded F_o sector. ATP synthesis is catalyzed by conformational changes within F₁, which are driven by the rotation of the c-ring (rotor) of F_o. The F_o motor is powered by the electrochemical gradient of H⁺ across the cell membrane, and movement of H⁺ through F_o is facilitated by two aqueous half-channels within subunit a (stator) and at the rotor-stator interface. The mechanism of how H⁺-driven rotation in F_o is generated is not fully understood. Cryo-electron microscopy has revealed structures of E. coli F₁F_o ATP synthase, but inconsistencies between this structural data and previous cross-linking data within subunit a suggest the existence of multiple conformations. In order to gain insight into suspected conformational dynamics of the stator, we have utilized site-directed spin labeling and electron paramagnetic resonance (EPR) spectroscopy to observe backbone mobility at several points in subunit a. We demonstrate the feasibility of this approach to report on the structure of subunit a and discuss the results of these mobility measurements.

Rashmi Shrestha

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