Rational Design of Covalent Multiheme Cytochrome‐Carbon Dot Biohybrids for Photoinduced Electron Transfer

Abstract

Biohybrid systems can combine inorganic light‐harvesting materials and whole‐cell biocatalysts to utilize solar energy for the production of chemicals and fuels. Whole‐cell biocatalysts have an intrinsic self‐repair ability and are able to produce a wide variety of multicarbon chemicals in a sustainable way with metabolic engineering. Current whole‐cell biohybrid systems have a yet undefined electron transfer pathway between the light‐absorber and metabolic enzymes, limiting rational design. To enable engineering of efficient electron transfer pathways, covalent biohybrids consisting of graphitic nitrogen doped carbon dots (g‐N‐CDs) and the outer‐membrane decaheme protein, MtrC from Shewanella oneidensis MR‐1 are developed. MtrC is a subunit of the MtrCAB protein complex, which provides a direct conduit for bidirectional electron exchange across the bacterial outer membrane. The g‐N‐CDs are functionalized with a maleimide moiety by either carbodiimide chemistry or acyl chloride activation and coupled to a surface‐exposed cysteine of a Y657C MtrC mutant. MtrC∼g‐N‐CD biohybrids are characterized by native and denaturing gel electrophoresis, chromatography, microscopy, and fluorescence lifetime spectroscopy. In the presence of a sacrificial electron donor, visible light irradiation of the MtrC∼g‐N‐CD biohybrids results in reduced MtrC. The biohybrids may find application in photoinduced transmembrane electron transfer in S. oneidensis MR‐1 for chemical synthesis in the future.

The role of semi-artificial photosynthetic systems in energy and environmental solutions: a critical review

“…Factors such as the stability and renderability of these components need to be carefully considered. It is important to note that conventional chemical-based electron donors and redox mediators may have issues related to toxicity and environmental impact, which could hinder their long-term sustainability and safety in real-world scenarios (Ye et al, 2022a;Zhang et al, 2023a). Zeng et al (2023b) developed SAPS by combining cobalt-based photosensitizers with nitrogen-fixing bacteria.…”

Engineering of bespoke photosensitiser–microbe interfaces for enhanced semi-artificial photosynthesis

“…(b) Non-specific covalent binding of a light-harvesting material to lysine residues at an enzyme surface (based on [NiFe]-hydrogenase): 122 proximity to the active site can again be investigated but not controlled via this method. (c) Specific covalent conjugation between a light-harvesting material and a transmembrane cytochrome (based on MtrCAB from S. oneidensis): 126 binding directly via an engineered cysteine residue allows targeting to an optimal site for electron injection into the redox protein. (d) Summary of the physical photosensitiser-protein binding methods discussed in this perspective.…”

“…A recent study from our group has addressed this challenge by rationally designing the covalent conjugation of MtrC with light-harvesting CD nanoparticles. 126,129 Previously, we coupled MtrC to Ru-based photosensitisers (a) adsorbed on TiO 2 nanoparticles 130 and (b) via site-specic covalent labelling. 131 The latter achieved ultrafast electron transfer on the ps timescale.…”

Bioinspired photocatalytic systems towards compartmentalized artificial photosynthesis

“…More recently, transmembrane electron transport in liposomes with reconstituted transmembrane cytochrome proteins was also reported by the groups of J. N. Butt, E. Reisner and L. J. C. Jeuken. The authors reported the integration of an icosa-haem transmembrane electron transfer protein (MtrCAB) 111 , 112 isolated from Shewanella oneidensis MR-1 into a liposome membrane. And demonstrated electron transport across the membrane towards the inner compartment of the liposomes where either a redox-active dye, reactive red 120 (RR120) 62 , or a N 2 O reductase enzyme 58 were encapsulated.…”