PMC

TM subunits are colored in blue and yellow with the inner subdomains (TM3/4/5/5a) highlighted in thicker ribbons (cyan and orange). The binding protein BtuF is colored purple and the ATPase subunits are colored in red and green.

A. Structures of the inward-facing molybdate/tungstate transporter AfModBC-A (left) and the outward-facing maltose transporter MalFGK₂-E (right). For each, the binding protein is colored in purple, the transmembrane subunits are colored in blue and yellow, and the ATPase subunits are colored in red and green. Translocation substrates, tungstate and maltose, are shown in CPK format while ATP is shown in ball-and-stick format. B. A model for alternating-access in ABC importers, modified from [].

A. Left, a slab view of the transmembrane cavity in the maltose transporter with the maltose substrate shown in CPK format. Residues of MBP that form the substrate-binding site in the open conformation are colored cyan. Right, a close-up view of the binding site with hydrogen bonds indicated by dashed lines. Figure modified from []. B. Ribbon representation of the methionine transporter (MetNI) and the molybdate/tungstate transporter (ModBC) in a “trans-inhibited” state. Substrates bound to the ATPase subunits are shown in CPK format.

A. Structure of the outward-facing Sav1866. One subunit is colored in blue (TMD) and green (NBD) and the other subunit in yellow (TMD) and red (NBD). The bound nucleotide, AMP-PNP is shown in ball-and-stick format. B. Structures of MsbA in open inward- (left), closed inward- (middle) and outward-facing (right) conformations. The extracellular loops (ECL) and cytoplasmic coupling helices (ICL) are indicated. C. Transitions from the open inward- to outward facing conformations. For each state TM1-6 (blue) of one TMD and TM4-5 (yellow) of the other TMD are shown. Rotations of TM4-5 (blue) and TM3-6 (blue) necessary for the transitions are indicated by black arrows.