The effect of conformational changes on non‐coordinated water occupancy associated with R and T allosteric states of Carp Hemoglobin

Abstract

The chemistry of non‐coordinated water molecules in the apolar internal environment of proteins is poorly understood. Our recent discovery of a spectral marker for the entry of noncoordinated water into the distal heme pocket of myoglobin has helped clarify this molecule's functional importance in ligand binding. We will apply our novel spectrokinetic assay to test the hypothesis that conformational changes can affect ligand binding indirectly by changing the occupancy of non‐coordinated water in apolar cavities. A comparison of the spectrokinetics between the visible and Soret spectral regions distinguishes protein relaxations from those associated with changes in internal water occupancy. Hemoglobin from Carp, Cyprinus carpio, shows differences in the putative water occupancy signal between the R and T allosteric states, which correspond to changes in ligand binding dynamics. These results suggest that conformational induced changes in water occupancy may play a role in allosteric induced changes in ligand binding dynamics. This knowledge will increase the understanding of the role these water molecules play in allosteric regulation.