International Collaboration in Chemistry: Protein Dynamics and Heme Protein Function

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The physiological processes catalyzed by human indole 2,3-dioxygenase and nitric oxide synthase, which involve the reaction between a diatomic ligand (O2, NO, CO), a substrate and the heme iron will be studied in detail to obtain an atomic-level description of the reaction mechanisms. This approach involves the analysis of protein structures, structural fluctuations and relaxations, and the dynamics of ligands and substrates within the protein. We will employ steady-state and time-resolved spectroscopic techniques with monitoring in the infrared and UV/visible regions of the spectrum. Ligands will be photodissociated by laser pulses, and the ensuing processes (ligand binding, substrate binding, protein relaxations etc.) will be observed over wide ranges of time and temperature (3 – 300 K). Measurements at cryogenic temperatures allow us to prepare and conserve rare and short-lived reaction intermediates, which can subsequently be analyzed in detail. These methods have been developed in recent years with myoglobin as a model system and have already been successfully applied to other heme proteins. Special emphasis will be put on reactions of the physiologically important ligand NO. To assess the influence of specific amino acids on the energy landscape and thus on active-site properties and ligand migration within and substrate binding to the protein, the proteins will be modified by site-directed mutagenesis.