25Survival under excess light conditions requires the light-induced accumulation of protein 26 LHCSR3 and other photoprotection factors, to enable efficient energy-dependent 27 quenching in the green microalga Chlamydomonas reinhardtii. Here, we demonstrate 28 that the high light-tolerant phenotype of mutant hit1 is caused by a de-repression of 29 promoters belonging to photoprotection genes, which in turn results from an inactivation 30 of the E3 ubiquitin ligase substrate adaptor LRS1. Transcriptome analyses of hit1 31 revealed massive alterations of gene expression modulation as a consequence of 32 perturbed LRS1 function, indicating its role as a crown regulator. In conjunction with 33 random forest-based network modeling, these transcriptome analyses predicted that 34 LRS1 controls photoprotection gene expression via an algal HY5 homolog as its prime 35 transcription factor target. CrHY5 binds to T-box elements present in the promoters of 36 these genes and its inactivation in the hit1 mutant via CRISPR-Cas9 genome editing, 37 confirmed the regulatory connection between LRS1 and CrHY5, predicted by the 38 network analysis. 39 40 41 42 43 44 45 46 47 48 54 Light provides the energy driving photosynthesis and it is an important cue controlling 55 many physiological processes in phototrophic organisms. In the seed plant Arabidopsis 56 thaliana the E3 ubiquitin ligase substrate adaptor COP1/SPA is a master switch of light 57 signaling, by repressing the accumulation of various transcription factors required for the 58 induction of light-dependent processes like photomorphogenesis or flowering in 59 darkness. Repression is achieved by ubiquitination of target transcription factors and 60
Edited by Norma AllewellThe facultative intracellular pathogen Listeria monocytogenes causes listeriosis, a rare but life-threatening disease. Host cell entry begins with activation of the human receptor tyrosine kinase MET through the bacterial invasion protein InlB, which contains an internalin domain, a B-repeat, and three GW domains. The internalin domain is known to bind MET, but no interaction partner is known for the B-repeat. Adding the B-repeat to the internalin domain potentiates MET activation and is required to stimulate Madin-Darby canine kidney (MDCK) cell scatter. Therefore, it has been hypothesized that the B-repeat may bind a co-receptor on host cells. To test this hypothesis, we mutated residues that might be important for binding an interaction partner. We identified two adjacent residues in strand 2 of the -grasp fold whose mutation abrogated induction of MDCK cell scatter. Biophysical analysis indicated that these mutations do not alter protein structure. We then tested these mutants in human HT-29 cells that, in contrast to the MDCK cells, were responsive to the internalin domain alone. These assays revealed a dominant negative effect, reducing the activity of a construct of the internalin domain and mutated B-repeat below that of the individual internalin domain. Phosphorylation assays of MET and its downstream targets AKT and ERK confirmed the dominant negative effect. Attempts to identify a host cell receptor for the B-repeat were not successful. We conclude that there is limited support for a co-receptor hypothesis and instead suggest that the B-repeat contributes to MET activation through low affinity homodimerization.
Bio-dyes for light harvesting in dye-sensitized solar cells (DSSC) have the advantage of being environmentally-friendly, non-toxic alternatives, which can be produced in a sustainable fashion. Free photosynthetic pigments are unstable in the presence of light and oxygen, a situation which can hardly be avoided during the operation of DSSCs, especially in large-scale applications. We therefore investigated the recombinant light-harvesting protein LHCBM6, which naturally occurs in the photosynthetic apparatus of the green microalga Chlamydomonas reinhardtii as a bio-dye in DSSCs. Photocurrent densities of up to 0.87 and 0.94 mA·cm−2 were determined for the DSSCs and solar energy to electricity conversion efficiencies (η) reached about 0.3% (100 mW·cm−2; AM 1.5 G filter applied). Importantly, we observed an unprecedented stability of LHCII-based DSSCs within long DSSC operation times of at least 7 days in continuous light and show that operation times are restricted by electrolyte decomposition rather than reduced dye performance, as could be demonstrated by DSSC reactivation following re-supplementation with fresh electrolyte. To the best of our knowledge, this is the first study analysing bio-dye sensitized DSSCs over such long periods, which revealed that during illumination an activation of the DSSCs occurs.
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