methane oxidation - monooxygenases - perfluoro carboxylic acids - protein tuning
Significance
The enzyme-catalyzed oxidation of simple liquid and gaseous alkanes,
among others methane, is reported. The biocatalytic system involved
uses a cytochrome P450 BM3 enzyme from Bacillus
megaterium, a heme-dependent monooxygenase, in combination
with perfluorinated carboxylic acids. The role of this acid additive is
to modulate guest-host interactions in the pocket, thus
triggering the catalytic activation as well as dramatically decreasing
the free space inside the binding pocket. With this lower translational
freedom, the approach of the alkane to the active center is facilitated
and increases the catalytic turnover in some cases by several orders
of magnitude. The experimental findings were further supported by
UV/Vis spectroscopy and molecular dynamics simulations,
also providing hints that for different alkane substrates different
acid additives might be essential.
Comment
The high potential of biocatalysis is unambiguous since it uses
environmentally benign reaction conditions paired with high catalytic
turnover numbers. To provide new biocatalysts the most commonly
accepted strategies are rational design of enzymes and directed
evolution towards more active mutants. Using a merger of these strategies,
Rao, Wong and co-workers, among others, were able to identify enzymes
capable of oxidizing rather simple alkanes (Angew.
Chem. Int. Ed. 2005, 44,
4029). The strategy presented in the current work, however, is much
simpler and can be considered as a chemical tuning, avoiding difficult
and time-consuming enzyme modifications. Since even the biocatalytic
oxidation of methane was realized, which is difficult to obtain otherwise,
this strategy will surely find more applications and stimulate further
research.
