Toward artificial photosynthesis

doi:10.1126/science.abc1226

GSTDTAP > 气候变化

DOI	10.1126/science.abc1226
	Toward artificial photosynthesis
	Nathaniel J. Gaut; Katarzyna P. Adamala
	2020-05-08
发表期刊	Science
出版年	2020
英文摘要	The creation of a fully artificial living cell would signify progress in both understanding current life and the development of synthetic organisms. A crucial component of any living organism is energy generation: the means to power its internal machinery. Because of their relative simplicity, catabolic reactions are the classical means for providing carbon and energy to synthetic cells, and much work has been done in optimizing which energy substrates work best for particular reactions ([ 1 ][1]). Despite robust success using small-molecule energy sources, the possibility of designing anabolic mechanisms that can harvest virtually limitless energy from light is very alluring yet remains unrealized. On page 649 of this issue, Miller et al. ([ 2 ][2]) leverage the capacity of microfluidics to combine natural and artificial biological networks to achieve photosynthetic anabolic reactions on a microscale level. Attempts at placing a series of complex reactions in a single, in vitro, cell-free protein expression platform generally have been plagued by low fidelity, irreproducibility, and small sample sizes. Within the past few decades, engineering of microfluidics to create artificial biological membranes has allowed these issues to be addressed ([ 3 ][3]). Microfluidic techniques allow for performing experiments in miniature cell culture systems in which cells and all reactants are exposed to dynamic fluid flow at the micrometer scale. The approach allows for the control of fluids through microchannels to change environmental conditions and provides opportunity for analyzing every cell separately (instead of looking at bulk cultures). Microfluidic barcoding ([ 4 ][4]) and screening ([ 5 ][5]) methods allow for easy synthesis and visualization of droplets (microscopic artificial “containers”) in a high-throughput manner. The rise of microfluidics has allowed milestone improvements in synthetic biology research through tighter reaction component titration and a virtually limitless sample size (because each droplet acts as its own discrete reaction compartment). The development of a synthetic liposome harboring functional adenosine triphosphate (ATP) synthase and bacteriorhodopsin to establish a proton gradient, and thus driving ATP synthesis, was a remarkable advancement in artificial photosynthesis ([ 6 ][6]). This system encompasses the basic function of photosynthesis: using light to synthesize an energy carrier molecule. An earlier study demonstrated encapsulation of these two protein complexes, purified separately, to harvest light energy and drive a variety of life-essential processes in liposomes, including high-energy molecule synthesis, carbon fixation, and actin polymerization ([ 7 ][7]). Both of those projects represent groundbreaking advancements toward creating light-powered artificial bioreactors as well as understanding the requirements for a photosynthetic system. However, more work is needed to realize a fully artificial photosynthetic cell. In this study by Miller et al. , membranes from thylakoids (compartments where the light-dependent reactions of photosynthesis take place) were isolated from the spinach plant ( Spinacia oleracea ) and encapsulated within water-in-oil droplets along with the 16 enzymes composing the crotonyl-coenzyme A (CoA)/ethylmalonyl-CoA/hydroxybutyryl-CoA (CETCH) pathway (see the figure). The CETCH pathway is a synthetic cycle for the continuous fixation of CO2, designed to complement the six naturally occurring carbon fixation pathways for use in in vitro models ([ 8 ][8]). The resulting encapsulated system uses light energy to produce the multicarbon molecule glycolate from CO2 while also phosphorylating adenosine diphosphate (ADP) to ATP, thereby successfully reconstituting an essential photosynthetic plant anabolic pathway. This design is validated experimentally by measuring an increase in ATP, reduced nicotinamide adenine dinucleotide phosphate (NADPH), and glycolate production upon illumination. Looking to expand this technology toward an easier bulk production method, the authors turned toward microfluidics to create thousands of water-in-oil droplets in an automated way. Using this scaled-up method of droplet production, they engineered precise control of the reaction conditions and visualized the reaction progression by imaging NADPH fluorescence. This advancement marks an important step toward the development of a synthetic plant-like cell. ![Figure][9] A technological approach to semisynthetic photosynthesis Thylakoids (where photosynthesis occurs) are purified from spinach, situated within oil-in-water droplets along with the 16 CETCH enzymes. When hit with light, the underlying reactions are triggered. This could be used in applications such as solar-powered bioreactors and engineering cells. GRAPHIC: MELISSA THOMAS BAUM/ SCIENCE Potential future challenges in this area include further inclusion of plant enzymes to incorporate the light-dependent or light-independent reactions that are essential to plant metabolism. This could be as simple as coupling this technology with the quasi–light-dependent synthetic system mentioned above ([ 6 ][6], [ 7 ][7]) or an independently developed reaction network that more closely borrows from pathways found in nature. Additionally, coupling this technology with one of the cell-free protein expression platforms, PURE (protein synthesis using recombinant elements) ([ 9 ][10]) or TXTL (whole-cell transcription-translation system) ([ 10 ][11]) would be a step toward a self-replicating system powered by endogenously expressed light-harvesting complexes. Using more complex microfluidics methods would enable encapsulation within a phospholipid bilayer membrane (liposomes are a monolayer lipid), resulting in better mimics of natural cells with the capacity for environmental interaction using natural transmembrane signaling tools ([ 11 ][12]). Combining energy generation with existing uses of cell-free and synthetic cell technologies would create a very powerful tool for biotechnology ([ 12 ][13]). Miller et al. demonstrate a major advancement in synthetic biology and a crucial milestone toward the construction of a self-sustaining synthetic cell. The ability to harvest light energy and fix CO2 into multicarbon compounds creates an essential foundation for technologies that will find use in many other areas, from small-molecule or drug synthesis in artificial bioreactors to development of an artificial biological system for sequestering environmental carbon. As we become better able to redesign and reconstruct natural biology, there will be many great leaps such as that achieved by Miller and colleagues in both understanding basic biological concepts as well as developing biotechnological innovations. 1. [↵][14]1. H. C. Kim, 2. D. M. Kim , J. Biosci. Bioeng. 108, 1 (2009). [OpenUrl][15][CrossRef][16][PubMed][17][Web of Science][18] 2. [↵][19]1. T. E. Miller et al ., Science 368, 649 (2020). [OpenUrl][20][Abstract/FREE Full Text][21] 3. [↵][22]1. D. N. Breslauer et al ., Mol. Biosyst. 2, 97 (2006). [OpenUrl][23][CrossRef][24][PubMed][25] 4. [↵][26]1. C. M. Svensson et al ., Small 15, 1 (2019). [OpenUrl][27][CrossRef][28] 5. 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领域	气候变化 ; 资源环境
URL	查看原文
引用统计
文献类型	期刊论文
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/249795
专题	气候变化资源环境科学
推荐引用方式 GB/T 7714	Nathaniel J. Gaut,Katarzyna P. Adamala. Toward artificial photosynthesis[J]. Science,2020.
APA	Nathaniel J. Gaut,&Katarzyna P. Adamala.(2020).Toward artificial photosynthesis.Science.
MLA	Nathaniel J. Gaut,et al."Toward artificial photosynthesis".Science (2020).