Figure 1

Membrane-protein models representing the two general categories of transmembrane-region structure. (a) Side-view of BtuCD Vitamin B12 Transporter [51] containing an α-helical transmembrane region (PDB accession code 1L7V); and (b) side-view of FecA Ferric Citrate Uptake Receptor [52] featuring a β-barrel transmembrane region (PDB accession code 1KMO). Light gray blocks on the sides of each model depict the approximate limits of the lipid bilayer. The figure was produced using MOLSCRIPT [53] and Raster3D [54].