FIGURE 3.

C-terminal domain of AlgX is a carbohydrate-binding module. Shown are schematic representations of the CBM, in red, showing the two antiparallel β-sheets organized into a β-jelly roll fold (A) and the superposition of the CBM (red) and P. equi CBM29-2 (PDB code 1GWK; gray) (B) in complex with mannohexaose. The Trp-400, Thr-398, Arg-364, and Arg-406 residues that comprise the substrate recognition pinch point are shown in yellow. Lys-396 and Lys-410, located outside the pinch point and postulated to play a role in directing the alginate polymer across the protein, are colored orange. C, surface representation of the CBM of AlgX showing the location of the superposed mannohexaose from P. equi CBM29-2. The oligosaccharide passes through the pinch point on the surface of the CBM.