Importance of Membrane Boundary Residues on the Rotor Ring of E. coli ATP Synthase

Abstract

ATP synthase is the primary producer in of adenosine triphosphate (ATP), the energy carrier molecule used in a variety of cellular processes. ATP synthase functions by using the proton gradient present across the cellular membrane to power a series of conformational changes resulting in the synthesis of ATP by a rotary mechansim. E. coli ATP synthase has two major parts, F1 and Fo, connected by the γ/ε stalk. Fo is membrane embedded and consists of subunits a, b2, and ten copies of subunit c, typically referred to as the c‐ring (or rotor). Protons enter through a half channel in the a subunit (stator) and are passed to the c‐ring, which rotates in a way that has protons exit on the low energy side of the membrane through a second half‐channel. Previous studies have shown that Cys substitutions at the membrane boundary of c‐ring (Phe54, Ile55, Tyr73, Phe76) can severely impact the function of the synthase, suggesting that these positions are important to the structure and/or function of the motor. Therefore, we have generated various substitutions at these residues to determine what chemical properties are needed in this region to support function. While the cytoplasmic boundary residues (54‐55) are surprisingly tolerant of mutation, substitutions at the periplasmic boundary residues (73‐76) reveal that reductions in both side chain size and hydrogen bonding capability impair activity of ATP synthase. These data help to characterize the interaction between the membrane‐embedded rotor and stator subunits.