Engineering Semi-Artificial Cells for New-to-Nature Photosynthesis
Lead Research Organisation:
University of Cambridge
Department Name: Chemistry
Abstract
Photosynthesis is an ancient process carried out by organisms including plants, algae and cyanobacteria, whereby sunlight is captured and converted to energy vectors that are then used to synthesis chemicals. However, natural photosynthetic processes were not evolved for efficiency. The ability to engineer more efficient and enhanced photosynthetic processes would lead to more promising sustainable ways of clean (bio)energy generation.
This project aims to build semi-artificial photosynthetic cells from the bottom up using a new biohybrid approach, to ultimately demonstrate how to engineer cells for enhanced or new-to-nature photosynthesis. The objectives towards this are to firstly isolate and modify the light harvesting/charge propagating component of photosynthesis (the thylakoids) to be able to convert more of the solar spectrum into usable energy/charge carriers. The second objective is to completely reprogram powerful CO2 concentrating capsules found in cyanobacteria, called carboxysomes, by replacing the naturally slow enzyme for CO2 conversion (RUBISCO) with much more efficient enzymes that can turn protons and CO2 into useful feedstocks including hydrogen gas and formate. The last objective is to encapsulate the two new biohybrid components into artificial cells so that the new 'light reaction' can be in close enough proximity to drive the new 'dark reactions'. This strategy will allow us to understand how to best tune the ratios of 'light' to 'dark' components within photosynthesis, as well as any intermediate energy carriers, to best balance the input and output fluxes and give rise to the most efficient light-to-chemical conversion systems.
This is a highly original approach for engineering photosynthetic cells that will likely yield new photosynthetic efficiencies or chemistries not possible using classical synthetic biology approaches. This work will provide valuable lessons into how photosynthetic cells can be bioengineered for bespoke performances in the future, which will benefit severl research areas beyond clean energy, including agriculture and bio-manufacturing.
This project aims to build semi-artificial photosynthetic cells from the bottom up using a new biohybrid approach, to ultimately demonstrate how to engineer cells for enhanced or new-to-nature photosynthesis. The objectives towards this are to firstly isolate and modify the light harvesting/charge propagating component of photosynthesis (the thylakoids) to be able to convert more of the solar spectrum into usable energy/charge carriers. The second objective is to completely reprogram powerful CO2 concentrating capsules found in cyanobacteria, called carboxysomes, by replacing the naturally slow enzyme for CO2 conversion (RUBISCO) with much more efficient enzymes that can turn protons and CO2 into useful feedstocks including hydrogen gas and formate. The last objective is to encapsulate the two new biohybrid components into artificial cells so that the new 'light reaction' can be in close enough proximity to drive the new 'dark reactions'. This strategy will allow us to understand how to best tune the ratios of 'light' to 'dark' components within photosynthesis, as well as any intermediate energy carriers, to best balance the input and output fluxes and give rise to the most efficient light-to-chemical conversion systems.
This is a highly original approach for engineering photosynthetic cells that will likely yield new photosynthetic efficiencies or chemistries not possible using classical synthetic biology approaches. This work will provide valuable lessons into how photosynthetic cells can be bioengineered for bespoke performances in the future, which will benefit severl research areas beyond clean energy, including agriculture and bio-manufacturing.
Technical Summary
The aim of this work is to deliver organelles and modular protocells for enhanced or new-to-nature photosynthesis. To achieve this, the first work package involves the purification of functional thylakoids, and the integration of synthetic light harvesters, such as molecule dyes with membrane targeting tails, into the purified thylakoids. This is done to facilitate the capturing of light normally missed by the naturally occurring chlorophylls, when the dyes are in close enough proximity to the chlorophylls, Forster Resonance Energy Transfer will be possible, effectively increasing the solar spectrum that can be utilised by the thylakoids. Coupled to this, synthetic mediators will be introduced to so that the increased influx of light will be matched by the rate of efflux of charges.
In the second work package, carboxysomes will be engineered to contained carbonic anhydrase, and RUBISCO will be replaced with hydrogenase/formate dehydrogenase. The combined effect of the carboxysome shell and the concentrated amount of carbonic anhydrase serves to deplete O2 within the interior of the shell and increase concentrations of CO2. This is highly favourable for both hydrogenases and CO2 reduction enzymes such as formate dehydrogenases. The carboxysomes walls will also be made conductive by introducing synthetic materials (e.g. carbon nanotubes) to bind to certain amino acid residues.
Lastly, the newly developed biohybrid thylakoids and carboxysomes will be confined together inside bilipid vesicles using an inverted emersion method or microfluidic strategies. Different ratios of each component will be encapsulated to optimise/match the fluxes of energy vectors liberated by one and consumed by another. During the engineering of all organelles and protocells, several characterisation techniques will be employed, including Joliot-Type-Spectroscopy, to provide feedback into the electron transfer rates through various parts of the photosynthetic electron transport chain.
In the second work package, carboxysomes will be engineered to contained carbonic anhydrase, and RUBISCO will be replaced with hydrogenase/formate dehydrogenase. The combined effect of the carboxysome shell and the concentrated amount of carbonic anhydrase serves to deplete O2 within the interior of the shell and increase concentrations of CO2. This is highly favourable for both hydrogenases and CO2 reduction enzymes such as formate dehydrogenases. The carboxysomes walls will also be made conductive by introducing synthetic materials (e.g. carbon nanotubes) to bind to certain amino acid residues.
Lastly, the newly developed biohybrid thylakoids and carboxysomes will be confined together inside bilipid vesicles using an inverted emersion method or microfluidic strategies. Different ratios of each component will be encapsulated to optimise/match the fluxes of energy vectors liberated by one and consumed by another. During the engineering of all organelles and protocells, several characterisation techniques will be employed, including Joliot-Type-Spectroscopy, to provide feedback into the electron transfer rates through various parts of the photosynthetic electron transport chain.
