 | Acta Crystallographica Section D Acta Crystallographica Section D BIOLOGICAL CRYSTALLOGRAPHY |
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![[Figure 2]](be5118fig2mag.jpg)
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Figure 2
Theoretical considerations of how two identical monomers could be arranged to form a dimer. In each of the panels the EmrE dimer is viewed perpendicular to the membrane plane with each helix labelled 1–4 in a different colour. The conserved faces of each helix are depicted as an arc of black and the position of Glu14 is shown as a small purple sphere on helix 1; biochemical data indicate that both Glu14 residues must be closely juxtaposed. The relative topology of each monomer in the membrane is depicted by either a plus (+) or a minus (−) sign. The relationship between monomer A and monomer B is considered in terms of the transition required to go from A to B. (a) Parallel dimers related by a translation; this is unlikely given that conserved residues in B are oriented towards the lipid bilayer. (b) Parallel dimers related by translation followed by 180° rotation of each helix about its axis perpendicular to the membrane plane; this is unlikely given that the interfaces between the helices in monomer A are different from the helices in monomer B. (c) Parallel dimers related by a twofold axis perpendicular to the membrane plane; this is unlikely given that the two Glu14 residues are on opposite sides of the molecule. (d) Antiparallel dimers related by an in-plane twofold axis (half arrows); this is likely provided that the cell can synthesize a membrane protein with both orientations in the membrane, i.e. dual topology. |
![[Figure 2]](be5118fig2.jpg)
| BIOLOGICAL CRYSTALLOGRAPHY |
ISSN: 1399-0047
