image: In vitro molecular assembly of PSII-based systems for photocurrent generation and enhanced ATP synthesis
In the recent decade, scientists have paid more attention to studying light harvest for producing novel bionic materials or integrating naturally biological components into synthetic systems. Inspiration is the imitation of natural photosynthesis in green plants, algae, and cyanobacteria to convert light energy into chemical energy. Photosystem II (PSII) is a light-intervened protein complex responsible for the light harvest and water splitting to release O2, protons, and electrons. The development of PSII-based biomimetic assembly in vitro is favorable for the investigation of photocatalysis, biological solar cells, and bionic photosynthesis, further help us reveal more secret of photosynthesis.
The combination of PSII and artificially synthetic structures is successful for making biohybrid assemblies to harvest light. The evolution of material science advances the development of PSII-based assemblies, PSII-mimicking hybrid systems, and utilization of PSII-related products for energy conversion. Relative applications and explorations occur through coupling PSII within lipid membranes, multilayer polymeric structures, and nanoparticles to maximize the efficient range of light absorbance and offer a high PSII payload yield.
The desired light-harvest performance enables a dramatic energy conversion from sunlight to electric power or biochemical energy. Apart from integrating with synthetic materials, naturally active components, photosystem I (PSI), bacteriorhodopsin (BR), or ATP synthase (ATPase), attain in vitro reassembly with PSII to form artificial chloroplasts and achieve partial natural photosynthesis process, including electron generation and transfer as well as ATP synthesis. Subsequent studies found that manipulation of light absorption range is critical to improving the photosynthetic activity of PSII. Synthetic luminescent materials (e.g., fluorescent polymers, quantum dots) are applied to help PSII or chloroplast convert UV light into visible light, resulting in productivity improvement of ATP synthesis.
At present, although reassembly of PSII-based hybrid systems is successful, this system suffers from typical drawbacks shares by common protein species in terms of stability, durability, biological activity, and environmental restrictions for applying PSII-based systems in the near future. Therefore, efforts and explorations still focus on investigating PSII-based biomimetic assembly to challenge these above weaknesses.
This Reviews Article published in National Science Review by Prof. Junbai Li's group at Beijing National Laboratory for Molecular Sciences, CAS Key Lab of Colloid, Interface and Chemical Thermodynamics, Institute of Chemistry of Chinese Academy of Sciences, summarizes recent studies on how PSII protein complex combines with artificial structures via molecular assembly, and highlights PSII-based semi-natural biosystems. Moreover, they discuss this biomimetic systems regarding the remaining problem, challenges, and outlooks.