M5: Bio-Hybrid and Enzyme Wiring Approaches
Wire photosynthetic proteins or redox enzymes to artificial electrodes for semi-artificial systems.
Idea
Directly incorporate components of natural photosynthesis or metabolisms – for example, wiring a photosynthetic protein (like Photosystem II or bacterial reaction centers) to artificial electrodes, or using redox enzymes (hydrogenases, CO₂-fixing enzymes) coupled with light absorbers.
Rationale
Instead of reinventing all charge-separation chemistry, one can use the finely tuned charge separation of natural proteins. For instance, researchers have connected Photosystem II to electrodes to extract electrons, or combined Photosystem I with a catalyst to make H₂ ("semi-artificial" systems). This leverages billions of years of evolution for the hard steps, while using human engineering to supply necessary parts.
Prerequisite Themes
Protein electrochemistry; enzyme immobilization techniques; lipid membranes or other matrices to support functional conformation outside cells.
Dependencies
Needs a source of light for the protein and then interfaces with catalysts or electrodes (for the H-stage). Often limited by stability (proteins can denature or quit working outside their native environment).
Signs of Progress
Successful long-lived electron transfer from a photosystem to an electrode or catalyst (hours or days of operation); engineered variants of enzymes that are more robust to oxygen or have broader spectrum absorption; hybrid devices that achieve measurable fuel production by coupling a biocomponent with an inorganic catalyst.
Base Camp M5.1: Fundamentals of Photosynthetic Protein Function
Scope: If using parts of living systems, you must know how they work in native context. Understand how photosystems absorb light, generate charge separation, and transfer electrons to natural cofactors.
Stepping-stones: Identify the redox cofactors inside PSII and PSI and their arrangement. Learn what stabilizes charge separation in PSI. Recognize limitations: these proteins need constant replacement of their D1 subunit (in PSII) due to damage.
Resources:
- Jordan, Peter et al. – "Three-dimensional structure of cyanobacterial photosystem I at 2.5 Å resolution," Nature 411.6840 (2001): 909–917. Why: Landmark paper that resolved PSI structure, giving insight into the complexity of the protein and the path electrons take.
- Umena, Yasufumi et al. – "Crystal structure of oxygen-evolving photosystem II at a resolution of 1.9 Å," Nature 473.7345 (2011): 55–60. Why: The high-resolution structure of PSII, including the Mn₄CaO₅ cluster. Informs how you might stabilize or connect to PSII artificially.
- Duarte, Ana et al. – "Isolation and characterization of a Photosystem II–reaction center–phycobilisome supercomplex from Synechocystis," Biochimica et Biophysica Acta (BBA) - Bioenergetics 1767.4 (2007): 272–279. Why: Gives an idea of methods to get these complexes out of cells and still functional.
Base Camp M5.2: Techniques for Wiring Proteins to Electrodes
Scope: Learn electrochemical communication with enzymes/proteins: how to attach a protein like a hydrogenase or photosystem to an electrode such that electrons can pass. This includes covalent attachment, adsorption on conductive nanomaterials, or encapsulation in polymers.
Stepping-stones: Look at an example of an enzyme electrode: hydrogenase on a graphite electrode. Consider the orientation problem. Study the concept of diffusion vs wired: a diffusional mediator can carry electrons from enzyme to electrode.
Resources:
- Willner, Itamar et al. – "Wiring of redox enzymes to electrodes by biomolecules," J Phys Chem B 101.36 (1997): 6670–6682. Why: A classic review on connecting enzymes to electrodes, covering various approaches.
- Armstrong, Fraser et al. – "Guiding Principles of Hydrogenase Catalysis Instigated by Protein Film Electrochemistry," Accounts of Chemical Research 46.10 (2013): 2055–2064. Why: Explains how to attach hydrogenase enzymes to electrodes and what insights were gained.
- Aziz, Shujahadeen et al. – "Harnessing Photosystem I for biophotovoltaics," J Mater Chem A 2.11 (2014): 3705–3717. Why: Concrete demonstration of wiring a photosystem to an electrode, including use of a polymer to keep it active.
Base Camp M5.3: Metabolic Engineering for Fuel Production
Scope: Understanding how one can rewire a microbe's metabolism to output a desired fuel. Even if you use whole cells rather than isolated proteins, you often need to tweak them. Learn basics of genetic engineering in cyanobacteria/algae.
Stepping-stones: Familiarize with some metabolic pathways for biofuel: the pathway from acetyl-CoA to butanol. Understand how electrons from photosynthetic electron transport can be redirected to these pathways via ferredoxin and NADPH.
Resources:
- Ducat, DC et al. – "Engineering cyanobacteria to generate high-value products," Trends in Biotechnology 29.2 (2011): 95–103. Why: A review that talks about genetic engineering of cyanobacteria for hydrogen, alcohols, etc.
- Leino, Hikari et al. – "Protein engineering of algal photoenzymes for biofuel production," Current Opinion in Biotechnology 59 (2019): 21–28. Why: Focuses on enzymes in algae that could be improved or altered for better fuel production.
- Angermayr, S. et al. – "Metabolic engineering of cyanobacteria for the synthesis of commodity products," Trends in Biotechnology 33.6 (2015): 352–361. Why: Overview of possible products and the metabolic pathways involved, complementing the Ducat review.