Redirecting Photosynthetic Electron Flow into Light-Driven Synthesis of Alternative Products Including High-Value Bioactive Natural Compounds

Abstract

Photosynthesis in plants, green algae, and cyanobacteria converts solar energy into chemical energy in the form of ATP and NADPH, both of which are used in primary metabolism. However, often more reducing power is generated by the photosystems than what is needed for primary metabolism. In this review, we discuss the development in the research field, focusing on how the photosystems can be used as synthetic biology building blocks to channel excess reducing power into light-driven production of alternative products. Plants synthesize a large number of high-value bioactive natural compounds. Some of the key enzymes catalyzing their biosynthesis are the cytochrome P450s situated in the endoplasmic reticulum. However, bioactive compounds are often synthesized in low quantities in the plants and are difficult to produce by chemical synthesis due to their often complex structures. Through a synthetic biology approach, enzymes with a requirement for reducing equivalents as cofactors, such as the cytochrome P450s, can be coupled directly to the photosynthetic energy output to obtain environmentally friendly production of complex chemical compounds. By relocating cytochrome P450s to the chloroplasts, reducing power can be diverted toward the reactions catalyzed by the cytochrome P450s. This provides a sustainable production method for high-value compounds that potentially can solve the problem of NADPH regeneration, which currently limits the biotechnological uses of cytochrome P450s. We describe the approaches that have been taken to couple enzymes to photosynthesis in vivo and to photosystem I in vitro and the challenges associated with this approach to develop new green production platforms.

Oxidation and cyclization of casbene in the biosynthesis of Euphorbia factors from mature seeds of Euphorbia lathyris L.

“…Knowledge on how to establish these carbon backbones offers the possibility to identify the subsequent enzymatic steps and to ultimately reconstruct the biosynthetic pathways of pharmaceutically active diterpenoids and new bioactive intermediates for biotechnological production. The recently reported option to redirect P450-dependent biosynthetic pathways into tobacco chloroplasts and drive the P450s directly based on light-driven photosynthetic electron transport using reduced ferredoxin as the direct electron donor to the P450s offers opportunities to redirect the production capacity of photosynthetic cells toward production of high levels of structurally complex diterpenoids (30,31).…”

Photosynthetic fuel for heterologous enzymes: the role of electron carrier proteins

“…Cytochrome P450s metabolize drugs and toxins in humans (Nebert et al 2013) and feature prominently in the biosynthesis of plant specialized metabolites of commercial interest such as terpenoids, alkaloids, and polyphenols (Renault et al 2014;Pateraki et al 2015). Consequently, they attract considerable attention for use in biotechnology and are frequently expressed in heterologous organisms and engineered for improved activity and recognition of new substrates (Fasan 2012;Lassen et al 2014b). The canonical cytochrome P450 reaction is the stereospecific hydroxylation on a substrate carbon atom (Eq.…”

The concept of photochemical enzyme models – State of the art

“…This very powerful shortcut pioneered by Willner and others [243] allows much faster progress for the optimization and practical application of light-mediated substrate conversion processes involving enzymatic catalysis steps. Research on such chemical-biochemical hybrid systems combining synthetic biology and photochemistry is therefore a rapidly emerging field which has been attracting growing interest within the last decade [244][245][246][247][248].…”