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. 2015 Jun 23;290(32):19597–19613. doi: 10.1074/jbc.M115.655654

FIGURE 7.

FIGURE 7.

Ligand discrimination by Epa6A and Epa1A binding pockets. A, binding pocket of Epa6A (blue) in complex with the T-antigen (yellow) and residues conferring binding affinity and specificity. A calcium ion (orange) is complexed via a DcisD motif and Asn-225. Interaction between Epa6A and the galactose moiety is accomplished by residues in CBL2 and Trp-198 of loop L3. B, binding mode of T-antigen to the pocket of Epa1A (gray) is similar to that of T-antigen to Epa6A, but the interaction pattern is different. The SigmaA-weighted 2Fobs − Fcalc electron density highlights the orientation of the carbohydrate (contoured at 2.0 σ). C–F, structures of the Epa6A binding pocket in complex with four different galactosides. Although the orientation of the terminal galactose moiety is fixed in all four complexes, the binding pose of the second hexose is more variable and depends on its type and the linkage to galactose.