Mechanism of methanol oxidation by quinoprotein methanol dehydrogenase.
At neutral pH, oxidation of CH(3)OH --> CH(2)O by an o-quinone requires general-base catalysis and the reaction is endothermic. The active-site -CO(2)(-) groups of Glu-171 and Asp-297 (Glu-171-CO(2)(-) and Asp-297-CO(2)(-)) have been considered as the required general base catalysts in the bacterial o-quinoprotein methanol dehydrogenase (MDH) reaction. Based on quantum mechanics/molecular mechanics (QM/MM) calculations, the free energy for MeOH reduction of o-PQQ when MeOH is hydrogen bonded to Glu-171-CO(2)(-) and the crystal water (Wat1) is hydrogen bonded to Asp-297-CO(2)(-) is DeltaG++ = 11.7 kcal/mol, which is comparable with the experimental value of 8.5 kcal/mol. The calculated DeltaG++ when MeOH is hydrogen bonded to Asp-297-CO(2)(-) is >50 kcal/mol. The Asp-297-CO(2)(-)...Wat1 complex is very stable. Molecular dynamics (MD) simulations on MDH.PQQ.Wat1 complex in TIP3P water for 5 ns does not result in interchange of Asp-297-CO(2)(-) bound Wat1 for a solvent water. Starting with Wat1 removed and MeOH hydrogen bonded to Asp-297-CO(2)(-), we find that MeOH returns to be hydrogen bonded to Glu-171-CO(2)(-) and Asp-297-CO(2)(-) coordinates to Ca(2+) during 3 ns simulation. The Asp-297-CO(2)(-)...Wat1 of reactant complex does play a crucial role in catalysis. By QM/MM calculation DeltaG++ = 1.1 kcal/mol for Asp-297-CO(2)(-) general-base catalysis of Wat1 hydration of the immediate CH(2)==O product --> CH(2)(OH)(2). By this means, the endothermic oxidation-reduction reaction is pulled such that the overall conversion of MeOH to CH(2)(OH)(2) is exothermic.
Zhang
Xiaodong
X
Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106, USA.
Reddy
Swarnalatha Y
SY
Bruice
Thomas C
TC
D000429:Alcohol Oxidoreductases / Q000737:chemistry* / Q000378:metabolism*; D001224:Aspartic Acid / Q000378:metabolism; D001665:Binding Sites; D002245:Carbon Dioxide / Q000737:chemistry / Q000378:metabolism; D002384:Catalysis; D003198:Computer Simulation; D018698:Glutamic Acid / Q000378:metabolism; D000432:Methanol / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D010084:Oxidation-Reduction; D017434:Protein Structure, Tertiary
D002245:Carbon Dioxide; D001224:Aspartic Acid; D018698:Glutamic Acid; D000429:Alcohol Oxidoreductases; C019641:alcohol dehydrogenase (acceptor); D000432:Methanol