Conformational Change Induced by ATP Binding in the Multidrug ATP-Binding Cassette Transporter BmrA † (original) (raw)

ATP-binding cassette (ABC) transporters are involved in the transport of a wide variety of substrates, and ATP-driven dimerization of their nucleotide binding domains (NBDs) has been suggested to be one of the most energetic steps of their catalytic cycle. Taking advantage of the propensity of BmrA, a bacterial multidrug resistance ABC transporter, to form stable, highly ordered ring-shaped structures ) J. Mol. Biol. 315, 1075-1085, we show here that addition of ATP in the presence of Mg 2+ prevented ring formation or destroyed the previously formed rings. To pinpoint the catalytic step responsible for such an effect, two classes of hydrolysis-deficient mutants were further studied. In contrast to hydrolytically inactive glutamate mutants that behaved essentially as the wild-type, lysine Walker A mutants formed ring-shaped structures even in the presence of ATP-Mg. Although the latter mutants still bound ATP-Mg, and even slowly hydrolyzed it for the K380R mutant, they were most likely unable to undergo a proper NBD dimerization upon ATP-Mg addition. The ATP-driven dimerization step, which was still permitted in glutamate mutants and led to a stable conformation suitable to monitor the growth of 2D crystals, appeared therefore responsible for destabilization of the BmrA ring structures. Our results provide direct visual evidence that the ATP-induced NBD dimerization triggers a conformational change large enough in BmrA to destabilize the rings, which is consistent with the assumption that this step might constitute the "power stroke" for ABC transporters. † This work was supported by CNRS Grant PGP 2002 (to A.D.P.), a CNRS Young Investigator ATIP Program to J.-M.J., and a grant (ANR-06-Blan-0420) from the Agence Nationale de la Recherche to