This subproject is one of many research subprojects utilizing theresources provided by a Center grant funded by NIH/NCRR. The subproject andinvestigator (PI) may have received primary funding from another NIH source,and thus could be represented in other CRISP entries. The institution listed isfor the Center, which is not necessarily the institution for the investigator.In previous molecular dynamics studies, we established the positioning of the methanol substrate at the active site of bacterial quinoneprotein methanol dehydrogenase (MDH). In the present study, we have employed QM/MM procedure to establish the reaction coordinate for MDH catalysis of the oxidation of methanol by the pyrroloquinoline quinone (PQQ) cofactor. The reaction involves Glu171-CO2- general-base catalysis of departure of the methanol hydroxyl proton with hydride equivalent transfer from the putative methoxide to quinone C5=O5 of PQQ. The transition state is late and following the Hammond postulate, the redox reaction is endothermic. The calculated free energy for the general-base catalyzed hydride transfer step (10.8 kcal/mol) is in agreement with the experimental Gibbs energy (8.5 kcal/mol). Comparisons of the electrostatic bond lengths and Mulliken partial charge in the ground and transition states support Ca2+ playing a role in the formation of the ground state active conformation and stabilization of the transition state. Ca2+ is ligated with Glu171-CO2- in the ground state but not in the transition state.
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