Fig. 5.

Model of the ABC exporter transport cycle. ABC transporters from the ABCB and the ABCC subfamily share the same sequence of conformational changes controlling the transport cycle and the structural asymmetry. While ABC proteins with a degenerate NBS (upper cycle) show NBD motions similar to a clamp‐shell by closing/opening only NBS2 during ATP binding, hydrolysis and ADP + Pi release, transporters with two canonical NBSs might function as a seesaw by occluding and hydrolyzing ATP in either NBS, but never simultaneously. The two types of NBDs might differ in the position of the hinge point and in their gates that open to release substrate to the extracellular site.