Figure 2. Topology and fold of MlaE.

(A) MlaE dimer, with one protomer represented as surface, and the other as cartoon. (B–J) comparison of MlaE (PDB 6XBD) with the related transmembrane domains of ABC transporters, MacB and LptFG (PDB 5GKO and 6MHZ). (B, E, H) Topology diagrams. CH, coupling helix; PH, periplasmic helix; IF, interfacial helix (also called connecting helix in ABCG transporters); TM, transmembrane helix. (C, F, I) Schematics representing helices at the dimer interface, viewed from the periplasm (each circle represents a helix). (D, G, J) Cartoon view of monomer. See Figure 2—figure supplement 1 for comparisons with additional related transporters.

Figure 2—figure supplement 1. Comparison of MlaE to other ABC transporters.

(A) MlaE, this paper, PDB 6XBD; (B) O-antigen transporter, PDB 6OIH; (C) TarG, PDB 6JBH; (D) ABCA1, PDB 5XJY, TMD2 shown; (E) ABCG5/G8, PDB 5DO7, G8 shown; (F) ABCG2, PDB 6HBU. Topology diagrams (first row); schematics representing helices at the dimer interface, viewed from the periplasm (each circle represents a helix) (second row); and cartoon views of monomers (third row) are shown.

Figure 2—figure supplement 2. Structural variation in MlaE TMD compared to other ABC transporters.

(A) TM5 helices (blue) are either a single continuous helix (MlaE, PDB 6XBD; LptG, PDB 6MHZ), a reentrant helix insertion (pink) (Wzm, PDB 6OIH; ABCG2, PDB 6HBU), or no helix (MacB, PDB 5GKO). (B) IF2 (brown) and TM1 (salmon) helices adopt a range of conformations, from IF2 being parallel to the membrane interface and forming a sharp angle with TM1 (left) to one continuous smooth helix for LptG (right). Top row, cartoon representation; bottom row, curvature color coded using Bendix (Dahl et al., 2012).