A construct containing the CBM22-1-CBM22-2 tandem forming the N-terminal domain of Paenibacillus barcinonensis xylanase 10C (Xyn10C) has been purified and crystallized. A xylan-binding function and an affinity for mixed β-1,3/β-1,4 glucans have previously been demonstrated for some members of the CBM22 family. The sequence of the tandem is homologous to the N-terminal domains found in several thermophilic enzymes. Crystals of this tandem were grown by the streak-seeding method after a long optimization strategy. The structure has been determined by molecular replacement to a resolution of 2.43 Å and refinement is under way. This study represents the first structure containing two contiguous CBM22 modules, which will contribute to a better understanding of the role that this multiplicity plays in fine-tuning substrate affinity.
Keywords: CBM22; Paenibacillus; bacterial xylanase; carbohydrate-binding domain; xylan-binding domain.