Abstract
Photosynthetic water-splitting is a powerful force to drive selective redox reactions. The need of highly expensive redox partners such as NADPH and their regeneration is one of the main bottlenecks for the application of biocatalysis at an industrial scale. Recently, the possibility of using the photosystem of cyanobacteria to supply high amounts of reduced nicotinamide to a recombinant enoate reductase opened a new strategy for overcoming this hurdle. This paper presents the expansion of the photosynthetic regeneration system to a Baeyer–Villiger monooxygenase. Despite the potential of this strategy, this work also presents some of the encountered challenges as well as possible solutions, which will require further investigation. The successful enzymatic oxygenation shows that cyanobacterial whole-cell biocatalysis is an applicable approach that allows fuelling selective oxyfunctionalisation reactions at the expense of light and water. Yet, several hurdles such as side-reactions and the cell-density limitation, probably due to self-shading of the cells, will have to be overcome on the way to synthetic applications.
Highlights
With an increasing awareness of global warming and a foreseeable depletion of fossil resources, the demand for clean synthetic processes has soared
The gene chmo, encoding the Baeyer–Villiger Monooxygenase with an N-terminal hexahistidine tag was inserted into a cassette under the light-induced promoter psbA2, and transformed into the naturally competent cyanobacterial cells
The observation of a drastically reduced reaction rate under darkness demonstrates that the majority of the redox equivalents originate from photosynthesis
Summary
With an increasing awareness of global warming and a foreseeable depletion of fossil resources, the demand for clean synthetic processes has soared. Redox transformations belong to the most important reactions in organic synthesis. Oxidoreductases, such as oxygenases, alcohol dehydrogenases, amine dehydrogenases, and ene-reductases selectively catalyse the introduction and modification of functional groups with often outstanding selectivity and under mild reaction conditions [1]. All these reactions require reduced electron donors, mostly nicotinamide cofactors. In synthetic applications, these external cofactors are recycled by using energy-rich organic molecules such as isopropanol or glucose as electron donors.
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