The interactions of the glucose units −2 and −1 with the strictly conserved GH-A clan residues, namely two glutamic acids, the catalytic nucleophile (259, here mutated to alanine) and the proton donor (118), and an asparagine (117) in front of the proton donor. (a) The structure of the present complex 7G shown in a 2Fo − Fc map (blue) contoured at 1σ. (b) The structure of the native protein (PDB entry 3ur7
; grey) shown after superposition on the complex structure, with the glucose residue −1 modelled in the 4H3 conformation (grey). This altered conformation reduces the degree of steric conflict with the side chain of the Glu259 nucleophile, which coincides with a water molecule in the mutant structure.