Extended Data Fig. 5: Copper coordination sphere in CelOCE.

(a) When glycerol, a sugar mimetic, is present (structure 2), one water molecule in the copper coordination sphere is replaced by an oxygen atom from glycerol. This causes the remaining water molecule to shift to the equatorial plane, alongside H44, H46, and Q50. (b) Conformational change in copper coordinating histidine at acidic pH. Comparison of two CelOCE crystal structures highlights a conformational change in H44 that occurs under acidic pH conditions. The structure obtained under acidic crystallization condition is shown in light orange (structure 3), while the CelOCE structure with non-flipped H44 is shown in white (structure 2) for comparison. The copper-coordinating residues are represented as sticks, the copper atom as an orange sphere, water molecules as red spheres and glycerol molecules as spheres/sticks following the protein color scheme. Distance measurements (in ångström) pertain to the structure obtained under acidic conditions, specifically showing the altered position of H44 relative to the copper.