X-Ray Crystal Structure of the Multidomain Endoglucanase Cel9G from Clostridium cellulolyticum Complexed with Natural and Synthetic Cello-Oligosaccharides

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Abstract
Complete cellulose degradation is the first step in the use of biomass as a source of renewable energy. To this end, the engineering of novel cellulase activity, the activity responsible for the hydrolysis of the β-1,4-glycosidic bonds in cellulose, is a topic of great interest. The high-resolution X-ray crystal structure of a multidomain endoglucanase from Clostridium cellulolyticum has been determined at a 1.6-Å resolution. The endoglucanase, Cel9G, is comprised of a family 9 catalytic domain attached to a family IIIc cellulose-binding domain. The two domains together form a flat platform onto which crystalline cellulose is suggested to bind and be fed into the active-site cleft for endolytic hydrolysis. To further dissect the structural basis of cellulose binding and hydrolysis, the structures of Cel9G in the presence of cellobiose, cellotriose, and a DP-10 thio-oligosaccharide inhibitor were resolved at resolutions of 1.7, 1.8, and 1.9 Å, respectively.