Identification and structural characterization of a novel chondroitin sulfate-specific carbohydrate-binding module: The first member of a new family, CBM100

Chondroitin sulfate is a biologically and commercially important polysaccharide with a variety of applications. Carbohydrate-binding module (CBM) is an important class of carbohydrate-binding protein, which could be utilized as a promising tool for the applications of polysaccharides. In the present study, an unknown function domain was explored from a putative chondroitin sulfate lyase in PL29 family. Recombinant PhCBM100 demonstrated binding capacity to chondroitin sulfates with Ka values of 2.1 +/- 0.2 x 106 M-1 and 6.0 +/- 0.1 x 106 M-1 to chondroitin sulfate A and chondroitin sulfate C, respectively. The 1.55 angstrom resolution X-ray crystal structure of PhCBM100 exhibited a I3-sandwich fold formed by two antiparallel I3-sheets. A binding groove in PhCBM100 interacting with chondroitin sulfate was subsequently identified, and the potential of PhCBM100 for visualization of chondroitin sulfate was evaluated. PhCBM100 is the first characterized chondroitin sulfatespecific CBM. The novelty of PhCBM100 proposed a new CBM family of CBM100.