A goose-type lysozyme from ostrich ( Struthio camelus ) egg white: multiple roles of His101 in its enzymatic reaction

Although the binding of tri- N -acetylchitotriose, (GlcNAc) 3 , to OEL perturbed several backbone resonances in the 1 H– 15 N HSQC spectrum, the chemical shift of the backbone resonance of His101 was not significantly affected.

However, apparent p K a values of His101 and Lys102 determined from the pH titration curves of the backbone chemical shifts were markedly shifted by (GlcNAc) 3 binding. Thermal unfolding experiments and modeling study of (GlcNAc) 6 hydrolysis using a His101-mutated OEL (H101A-OEL) revealed that the His101 mutation affected not only sugar residue affinities at subsites −3 and −2 but also the rate constant for bond cleavage.