Functional Extraction and Spectroscopic Investigation of Structural Dynamics in E. coli ATP Synthase

Abstract

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 Fo sector. ATP synthesis is catalyzed by conformational changes within F1, which are driven by the rotation of the c‐ring (rotor) of Fo. The Fo motor is powered by the electrochemical gradient of H+ across the cell membrane, and movement of H+ through Fo 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 Fo is generated is not fully understood. Cryo‐electron microscopy has revealed structures of E. coli F1Fo 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 membrane extraction using mixed micelles of dodecylmaltoside/phosphatidylcholine or styrene maleic acid lipid particles (SMALPs). Furthermore, we found high backbone mobility at sites on the cytoplasmic surface of the subunit a stator.