Transmembrane Shuttling of Photosynthetically Produced Electrons to Propel Extracellular Biocatalytic Redox Reactions in a Modular Fashion

Abstract

Many biocatalytic redox reactions depend on the cofactor NAD(P)H, which may be provided by dedicated recycling systems. Exploiting light and water for NADPH‐regeneration as it is performed, e.g. by cyanobacteria, is conceptually very appealing due to its high atom economy. However, the current use of cyanobacteria is limited, e.g. by challenging and time‐consuming heterologous enzyme expression in cyanobacteria as well as limitations of substrate or product transport through the cell wall. Here we establish a transmembrane electron shuttling system propelled by the cyanobacterial photosynthesis to drive extracellular NAD(P)H‐dependent redox reactions. The modular photo‐electron shuttling (MPS) overcomes the need for cloning and problems associated with enzyme‐ or substrate‐toxicity and substrate uptake. The MPS was demonstrated on four classes of enzymes with 19 enzymes and various types of substrates, reaching conversions of up to 99 % and giving products with >99 % optical purity.

Photobiocatalytic Strategies for Organic Synthesis

“…To overcome this issue, they developed a shuttling strategy where acetone would shuttle reducing equivalents from a cyanobacterium to biocatalysts in solution (Figure 82A). 235 The cyanobacterium (Synechococcus elongatus PCC 7942) heterologously expressing the alcohol dehydrogenase from Lactobacillus kefir (Lk-ADH) reduces acetone to i-PrOH using photosynthetically produced NADPH (Module A). After passing through the cell membrane, i-PrOH is oxidized by the Lk-ADH to produce NADPH (Module B), which can be used by the enzyme of interest to modify a substrate (Module C).…”

Evaluating scaling of capillary photo‐biofilm reactors for high cell density cultivation of mixed trophies artificial microbial consortia

“…Photoautotrophic microbes can produce chemicals and value-added compounds directly from carbon dioxide fueled by light as an energy source [1]. Nowadays, phototrophic microbes produce vitamins and pigments on a large scale [2,3], while the expanding metabolic engineering and synthetic biology toolboxes are tremendously broadening the number of accessible compounds [4,5]. These applications commonly utilize suspended cell cultures, which inherit several drawbacks, such as low biomass caused by light limitation, high O 2 accumulation, and low product titers [4].…”