ATP Synthase: Elastic Power Transmission Between Two Rotary Stepper Motors

Professor Wolfgang Junge
University of Osnabrueck
Germany

Thursday, June 13, 2002
10:00 am
3269 Beckman Institute

Abstract

ATP synthase (F-ATPase) produces ATP at the expense of ionmotive force or vice versa. It is composed from two rotary motor/generators, the ATPase (F1) and the ion translocator (FO). Both are rotary steppers. The enzyme copes with symmetry mismatch (C3 versus C10-14) between these motors, and it operates robustly in chimeric constructs or with drastically modified subunits. We scrutinized whether an elastic power transmission accounts for these properties. Using the curvature of an fluorescent actin filaments, attached to the rotating c ring of FO, as a spring balance (flexural rigidity of 8·10-26 Nm2) we gauged the angular torque profile at at FO as generated by ATP hydrolysis in F1. The large average torque (56 pN⋅nm) proved the absence of slip. That the angular torque variations were small implied a soft elastic power transmission between F1 and FO. It is considered as essential, not only for the robust operation of this ubiquitous enzyme under symmetry mismatch, but also for a high turnover under load of this fascinating nano- maschine.