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Figure 3.
Fig. 3. EmrE binds TPP as an antiparallel dimer. (A)
Stereoview of the EmrE transporter in complex with TPP. The two
monomers are colored blue and yellow, and the bound TPP is pink.
Anomalous Fourier density from SeMet (colored red in one monomer
and green in the other) and the arsonium analogue of TPP
(magenta) are shown contoured at 3  and 3.5 ,
respectively. The TPP and SeMet residue positions are labeled,
with the two monomers distinguished by asterisks. (B) "Front"
view of the transporter, emphasizing the positions of SeMet
markers in TM1. The N termini of the monomers are labeled. (C)
"Top" view of the EmrE-TPP structure, with the TM helices
labeled. Red spheres indicate the positions of residues that
have been implicated in substrate binding and transport by
biochemical and mutagenesis studies (18, 20, 23–28). The only
residue removed from the binding chamber is Leu-93 (TM4). In the
x-ray crystals, this residue appears to mediate lattice
interactions across a twofold symmetry axis relating two dimers.
This crystal packing interface was also observed in the
two-dimensional crystals used to derive the EM structure of
EmrE-TPP (14).
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