An exceptional variability in the motor of archaeal A1A0 ATPases:: From multimeric to monomeric rotors comprising 6-13 ion binding sites

The motor domain of A(1)A(0) ATPases is composed of only two subunits, the stator subunit I and the rotor subunit c. Recent studies on the molecular biology of the A(0) domains revealed the surprising finding that the gene encoding subunit c underwent several multiplication events leading to rotor subunits comprising 2, 3, or even 13 hairpin domains suggesting multimeric in different stoichiometry as well as monomeric rotors. The number of ion translocating groups per rotor ranges from 13 to 6. Furthermore, as deduced from the gene sequences H+- as well as Na+-driven rotors are found in archaea. Features previously thought to be distinctive for A(0), F-0, or V-0 are all found in A(0) suggesting that the differences encountered in the three classes of ATPases today emerged already very early in evolution. The extraordinary features and exceptional structural and functional variabilty in the rotor of A(1)A(0) ATPases may have arisen as an adaptation to different cellular needs and the extreme physicochemical conditions in the early history of life.