(475f) Particulate Methane Monooxygenase-Catalyzed Sustainable Methanol Production from Atmospheric Methane

The ability of Methanotrophic bacteria to produce methanol from atmospheric methane by Methane Monooxygenase (MMO) enzyme, and further oxidize methanol to formaldehyde by Methanol Dehydrogenase (MDH) enzyme is an exciting phenomenon, since it implies that the organism can change product and substrate reversibly depending on the prevailing conditions. Understanding how these two enzymes, that are present in Methanotrophic bacteria, work in nature will provide clues to designing efficient synthetic catalysts (through biomimetics), which can mitigate the harmful effects of methane in the atmosphere, leading to a reduction in global warming.

Particulate Methane Monooxygenase(pMMO), a MMO form that is expressed when the growth medium contains copper at sufficient levels (>5µM) under high copper/biomass ratios, is the predominant methane oxidation catalyst in nature.[1] Lieberman et al.[2] suggested that the active site of pMMO is constructed partially (with 50% of the copper) of a multi-copper complex, although the nuclearity of the Cu cluster in pMMO is still unknown. Hence, clues on how pMMO activates the inert methane C-H bond are of fundamental chemical interest, and could lead to the development of new synthetic catalysts that could impact the use of methane (natural gas) as an alternative energy source.

This work focuses on fundamental research on the kinetics of an important catalyzed chemical reaction that relates to environmental biocatalysis, and involves atmospheric methane consumption (oxidation) for the production of fuel (methanol). Molecular Mechanics and Molecular Dynamics simulations are conducted in order to investigate the processes involved in methanol production by pMMO, looking at its interaction with MDH. In this work, models of MDH and pMMO are selected and geometry minimized first. Then, their interaction is investigated and tested upon the addition of oxidized forms of methane and methanol representing possible reaction steps in those oxidation mechanisms. The results from the simulations will provide clues on the location of the pMMO active site and its ability to break the methane C-H bond.

[1] S.K. Dubey, A.S.K. Sinha, and J.S. Singh, Differential inhibition of CH4 oxidation in bare, bulk and rhizosphere soils of dryland rice field by nitrogen fertilizers, Basic and Applied Ecology, 3. 2002. p. 347-355.

[2] R.L. Lieberman and A.C. Rosenzweig, Crystal structure of a membrane-bound metalloenzyme that catalyses the biological oxidation of methane, Nature, 434. 2005. p. 177-182.