Topology models of anion exchanger 1 that incorporate the anti-parallel V-shaped motifs found in the EM structure

We recently published the three-dimensional structure of the membrane domain of human erythrocyte anion exchanger 1 (AE1) at 7.5 ? resolution, solved by electron crystallography. The structure exhibited distinctive anti-parallel V-shaped motifs, which protrude from the membrane bilayer on both sides. Similar motifs exist in the previously reported structure of a bacterial chloride channel (ClC)-type protein. Here, we propose two topology models of AE1 that reflect the anti-parallel V-shaped structural motifs. One is assumed to have structural similarity with the ClC protein and the other is only assumed to have internal repeats, as is often the case with transporters. Both models are consistent with most topological results reported thus far for AE1, each having advantages and disadvantages.