Figure 4.

The peptide-binding site. Stereo view of the central cavity as viewed from above on the extracellular side of the membrane. Conserved residues between PepT_So and the mammalian peptide transporters are labelled and coloured according to side-chain type, Arg and Lys (blue), Glu and Ser (red), Tyr (green) and Trp, Phe and Leu (cyan). A di-peptide sized C_α baton (orange) is fitted as a size reference into the mFo-DFc electron density observed in the central cavity (blue mesh), contoured at 4 σ.