Figure 2 - full size

Figure 2. Fig. 2. Structure determination of EmrE. (A) Experimental density for one apo EmrE monomer at 4.5-Å resolution. Anomalous Hg density (4 ), marking the positions of cysteine residues, is shown in red. The protein is shown in C^ trace and rendered in a color gradient, from green at the N terminus to yellow at the C terminus. (B) Ribbon representation of the distorted apo EmrE dimer. One monomer is rendered in color gradient with the helices labeled, and the other monomer is shown in gray. The approximate dimensions of a lipid bilayer are shown by the gray shading. (C) Views of the two apo EmrE monomers, with TM helices labeled. Note the extended configuration of the TM4 helices, which project away from the main body of the dimer. (D) Experimental density for one monomer of the EmrE-TPP complex at 3.8 Å (C2 crystal form), contoured at 1 . Anomalous Se density (3 ) is shown in red. (E) Side view of the EmrE-TPP dimer (C2 form), with the dimensions of the lipid bilayer indicated. One monomer is colored in gradient and labeled, and the other is in gray. The bound TPP is colored red. Density for the colored monomer terminates at residue 105. (F) Views of the two monomers (P2[1] form), which are essentially the same as the C2 monomers, except for the shorter TM helices, which terminate at the indicated residues. Full-length EmrE has 110 amino acid residues. Note that the superhelical twists of TM1–3 are similar in the apo and TPP-bound forms but that the helix packing interactions and monomer–monomer interactions differ.