Coordination and binding of ions in Ca2+- and Ba2+-containing methanol dehydrogenase and interactions with methanol

Models representing the active sites of Ca2+- and Ba2+-containing methanol dehydrogenase (MDH) enzymes and their interaction with methanol are investigated using density functional theory methods and a continuum solvation model (PCM). Information on structure and energetics of such models in gas phase and implicit water solvent environments are obtained at the B3PW91/6-311+G** theory levels. Solvent binding energy calculations of the ions indicate that Ca2+ binding to the rest of the MDH active site model under consideration is 0.2-1.0 eV more stable than that of Ba2+. Also the nature of the ion modifies the orientation and binding of the methanol to the MDH model. The hydroxyl oxygen (O16) of methanol is better coordinated with Ba2+ than Ca2+ in MDH models, which may make the initial proton abstraction during the methanol oxidation by MDH in Ba2+-containing enzymes easier than that in Ca2+-containing MDH enzymes.