Fig. 5. Substrate specificity of AbfA and Cel5A. Superposition of the Michaelis complexes of AbfA with 4-nitrophenyl-Ara and Cel5A endoglucanase with 2,4-dinitrophenyl-2-deoxy-2-fluoro-β-d-cellobioside (PDB code: 1H2J). Only the catalytic residues and the residues responsible for the discrimination between the d-glucopyranosidic and l-arabinofuranosidic substrates are shown. Color coding: red, oxygen; blue, nitrogen; white, fluorine; yellow, carbon atoms of AbfA; light blue, carbon atoms of Cel5A.