Figure 4. The structures of the transmembrane domains (TMDs) and regulatory domains (RDs).

(A) Two views of the TMDs. EH1, EH2, and TM5 are highlighted in blue, and EH3, EH4, and TM11 are in green. The side chain of residues making inter-subunit contacts is shown as stick model. Lipids are shown in yellow. (B) Electrostatic surface representation of the TMDs, calculated assuming a pH of 7 and a concentration of 0.15 M of both (+1) and (−1) ions. Scale: red, negative (−5 kT/e); blue, positive (+5 kT/e). The EH1-turn-EH2 insertion is highlighted as blue ribbon. (C) An orthogonal view of (B), highlighting the hydrophilic indentation formed by the EH3-turn-EH4 insertion. (D) The RDs exhibit the ACT-like fold with the βαββαβ topology. EH: exocytoplasmic helices.

Figure 4—figure supplement 1. The ACT motifs and the pinning helices (PHs) are conserved in the ABCA subfamily.

Sequence alignment and secondary structure prediction of (A) RD1 and (B) RD2, output of PROMALS3D (Pei et al., 2008). RD: regulatory domain.