The Ancestry and Function of Cytochrome c6A

Cytochrome c6A is a homologue of cytochrome c6 found in eukaryotic green algae and higher plants. However it is thought to perform a different function from cytochrome c6. Two current hypotheses exist for this function: that cytochrome c6A acts as a ‘safety valve’, providing an alternative path for electron flow through the photosynthetic electron transport chain and thus alleviating reactive oxygen species production; that cytochrome c6A has a signalling role where it could sense high light stress and convey this signal to the nucleus to affect gene expression. This study aims to provide insight into the ancestry and function of cytochrome c6A. To gain a clearer understanding of the evolutionary history of cytochrome c6A and cyanobacterial homologues cytochrome c6B and c6C, phylogenetic analysis was performed on peptide sequences of these proteins as found in a wide range of photosynthetic organisms. These data were used to refine the model of the evolutionary history of the cytochrome c6 family. This study also found evidence that cytochrome c6B and c6C are in fact orthologues with a similar function. Chlamydomonas reinhardtii is a model organism for eukaryotic photosynthesis, as its unicellularity provides many advantages over land plants. To determine if cytochrome c6A is involved in high light stress in C. reinhardtii, cytochrome c6A knockout and knockdown mutant lines of C. reinhardtii had been previously produced using CrispR-cpf,1 and are characterised in this study. The mutant lines demonstrated potential growth retardation under high or fluctuating light stress, as well as singlet oxygen stress, which was more noticeable under mixotrophic conditions. Chlorophyll fluorescence analysis of the mutant lines established a link between cytochrome c6A and NPQ. As cytochrome c6A is believed to be located in the thylakoid lumen, and initial NPQ is triggered by a change in luminal pH, circular dichroism was used to determine changes in secondary structure of purified cytochrome c6A over a pH range of 2-7. No significant change in structure was observed, but cytochrome c6A did maintain structural integrity even at pH 2. Finally, the transcriptome of the cytochrome c6A knock out line was compared to the background strain under standard and high light conditions through RNAseq. Many photoprotective, motility and CCM genes were differentially regulated under high light stress, but when cytochrome c6A was knocked out these regulations were diminished. Therefore cytochrome c6A has been proposed as a signalling molecule that functions in CCM, NPQ and motility under photosynthetic stress conditions.BBSRC funded DT

Solar Water Splitting with a Hydrogenase Integrated in Photoelectrochemical Tandem Cells

Hydrogenases (H2ases) are benchmark electrocatalysts for H2 production, both in biology and (photo)catalysis in vitro. We report the tailoring of a p-type Si photocathode for optimal loading and wiring of H2ase through the introduction of a hierarchical inverse opal (IO) TiO2 interlayer. This proton-reducing Si j IO-TiO2 j H2ase photocathode is capable of driving overall water splitting in combination with a photoanode. We demonstrate unassisted (bias-free) water splitting by wiring Si j IO-TiO2 j H2ase to a modified BiVO4 photoanode in a photoelectrochemical (PEC) cell during several hours of irradiation. Connecting the Si j IO-TiO2 j H2ase to a photosystem II (PSII) photoanode provides proof of concept for an engineered Z-scheme that replaces the non-complementary, natural light absorber photosystem I with a complementary abiotic silicon photocathode

The Evolution of the Cytochrome c6 Family of Photosynthetic Electron Transfer Proteins.

During photosynthesis, electrons are transferred between the cytochrome b6f complex and photosystem I. This is carried out by the protein plastocyanin in plant chloroplasts, or by either plastocyanin or cytochrome c6 in many cyanobacteria and eukaryotic algal species. There are three further cytochrome c6 homologs: cytochrome c6A in plants and green algae, and cytochromes c6B and c6C in cyanobacteria. The function of these proteins is unknown. Here, we present a comprehensive analysis of the evolutionary relationship between the members of the cytochrome c6 family in photosynthetic organisms. Our phylogenetic analyses show that cytochromes c6B and c6C are likely to be orthologs that arose from a duplication of cytochrome c6, but that there is no evidence for separate origins for cytochromes c6B and c6C. We therefore propose renaming cytochrome c6C as cytochrome c6B. We show that cytochrome c6A is likely to have arisen from cytochrome c6B rather than by an independent duplication of cytochrome c6, and present evidence for an independent origin of a protein with some of the features of cytochrome c6A in peridinin dinoflagellates. We conclude with a new comprehensive model of the evolution of the cytochrome c6 family which is an integral part of understanding the function of the enigmatic cytochrome c6 homologs.German Academic Scholarship, Gates Cambridge Trust, Benn Levy Trust, Gordon & Betty Moore Foundatio

Raw data supporting article: Solar Water Splitting with a Hydrogenase Integrated in Photoelectrochemical Tandem Cells

Raw Data/Measurement results supporting article: Solar Water Splitting with a Hydrogenase Integrated in Photoelectrochemical Tandem Cell