Advances in structure-function relationships of tyrosinase from Agaricus bisporus - Investigation on heat-induced conformational changes

A combination of fluorescence spectroscopic measurements, inactivation kinetics and in silico prediction was used in the present study to investigate the heat induced behaviour of tyrosinase from Agaricus bisporus. The phase diagram indicated the existence of at least two distinct species induced by the temperature increase up to 75 °C. Regardless of calcium ion presence, the fluorescence intensity results suggest that tyrosinase tends to form aggregates after 10 min at 75 °C. The quenching experiments using acrylamide and iodide demonstrate a more flexible conformation of tyrosinase at higher temperature. Detailed insights into tyrosinase structure after performing molecular dynamics simulations, suggest important structural rearrangements of the protein with the temperature increase. The copper coordinating His94 residue was predicted to be involved in salt bridge formation with Glu98, therefore causing significant alteration of the substrate binding site with increasing temperature. These significant changes in tyrosinase structure at temperatures over 60 °C might lead to enzyme inactivation.