Fig. 4

The putative TAP model by Voss et al. (32). (A) Membrane topology of TAP. The light gray regions represent the transmembrane domains, the dark gray regions indicate potential peptide-binding domains, and the regions marked in black represent the ATP-binding sites. (B) The head-head/tail-tail orientation of TAP1 and TAP2 in the ER membrane shown from the ER in top view forming a pore for peptide translocation.