Family 17 and 28 carbohydrate-binding modules discriminated different cell-wall sites in sweet potato roots.

Endoglucanase Cel5A from Clostridium josui contains a family 17 carbohydrate-binding module (CBM) (CjCBM17) and a family 28 CBM (CjCBM28) in tandem. These two CBMs bound to non-crystalline cellulose and beta-1,3-1,4-glucan. Our results indicate that the CBMs recognized different components on the cell wall of a sweet potato root. The root was cut into longitudinal sections. We used CjCBM17 and CjCBM28 fused to two different fluorescent proteins to visualize differential recognition of the plant cell wall. When they were microscopically observed, CjCBM28-fused cyan fluorescent protein (CFP) differentially bound to the root cap, but CjCBM17-fused blue fluorescent protein (BFP) did not. CjCBM17-BFP bound to the central part or the root apical meristem. These results suggest that CjCBM17 and CjCBM28 recognize different sites of the cell wall and that the cell-wall components and the polysaccharides configuration in the cell wall differ between tissues.