The second stalk of Escherichia coli ATP synthase

Two stalks link the F-1 and F-0 sectors of ATP synthase. The central stalk contains the gamma and epsilon subunits and is thought to function in rotational catalysis as a rotor driving conformational changes in the catalytic alpha(3)beta(3) complex. The two b subunits and the delta subunit associate to form b(2)delta, a second, peripheral stalk extending from the membrane up the side of alpha(3)beta(3) and binding to the N-terminal regions of the a subunits, which are approx. 125 Angstrom from the membrane. This second stalk is essential for binding F-1 to F-0 and is believed to function as a stator during rotational catalysis. In vitro, b(2)delta is a highly extended complex held together by weak interactions. Recent work has identified the domains of b which are essential for dimerization and for interaction with delta. Disulphide cross-linking studies imply that the second stalk is a permanent structure which remains associated with one alpha subunit or alpha beta pair. However, the weak interactions between the polypeptides in b2 delta pose a challenge for the proposed stator function. (C) 2000 Elsevier Science B.V. All rights reserved.