Solution structure of the cellulose-binding domain of endoglucanase I from Trichoderma reesei and its interaction with cello-oligosaccharides

The solution structure of a synthetic 38‐residue cellulose‐binding domain (CBD) of endoglucanase I from Trichoderma reesei (CBD_EGI) was determined by two‐dimensional ¹H‐NMR spectroscopy. 100 structures were generated from a total of 599 NOE derived distance restraints and 28 φ and 14 χ dihedral angle restraints. For the final set of 19 selected structures, the rms deviation about the mean structure was 0.83 ± 0.26 Å for all atoms and 0.50 ± 0.22 Å for the backbone atoms. The structure of CBD_EGI was very similar to that of CBD of cellobiohydrolase I from T. reesei (CBD_CBHI). The backbone trace of CBD_EGI followed closely the irregular triple‐stranded antiparallel β‐sheet structure of CBD_CBHI. Moreover, apart from the different side chains of Trp7 (CBD_EGI) and Tyr5 (CBD_CBHI), the cellulose‐binding face of CBD_EGI was similar to that of CBD_CBHI within the precision of the structures. Finally, the interaction between CBD_EGI and soluble sugars was investigated using cellopentaose and cellohexaose as substrates. Experiments showed that the interactions between CBD_EGI and cellobiose units of sugars are specific, supporting the previously presented model for the CBD binding to crystalline cellulose.