Extremely robust photocurrent generation of titanium dioxide photoanodes bio-sensitized with recombinant microalgal light-harvesting proteins.

Lämmermann N, Schmid-Michels F, Weissmann A, Wobbe L, Hütten A, Kruse O. Extremely robust photocurrent generation of titanium dioxide photoanodes bio-sensitized with recombinant microalgal light-harvesting proteins. Scientific reports. 2019;9(1): 2109.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

Lichtsammlung in Chlamydomonas reinhardtii: In vitro-Nutzung in Solarzellen und in vivo Regulation über Lichtsignalkaskaden

Lämmermann N. Lichtsammlung in Chlamydomonas reinhardtii: In vitro-Nutzung in Solarzellen und in vivo Regulation über Lichtsignalkaskaden. Bielefeld: Universität Bielefeld; 2019

MET-activating Residues in the B-repeat of theListeria monocytogenesInvasion Protein InlB

Bleymüller W, Lämmermann N, Ebbes M, Maynard D, Geerds C, Niemann H. MET-activating Residues in the B-repeat of theListeria monocytogenesInvasion Protein InlB. Journal of Biological Chemistry. 2016;291(49):25567-25577.The 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 Darbey 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 beta2 of the beta-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 which, 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. Copyright 2016, The American Society for Biochemistry and Molecular Biology

Ubiquitin ligase component LRS1 and transcription factor CrHy5 act as a light switch for photoprotection in Chlamydomonas

Lämmermann N, Wulf D, Chang KS, et al. Ubiquitin ligase component LRS1 and transcription factor CrHy5 act as a light switch for photoprotection in Chlamydomonas. bioRxiv. 2020.Survival under excess light conditions requires the light-induced accumulation of protein LHCSR3 and other photoprotection factors, to enable efficient energy-dependent quenching in the green microalgaChlamydomonas reinhardtii. Here, we demonstrate that the high light-tolerant phenotype of mutanthit1is caused by a de-repression of promoters belonging to photoprotection genes, which in turn results from an inactivation of the E3 ubiquitin ligase substrate adaptor LRS1. Transcriptome analyses ofhit1revealed massive alterations of gene expression modulation as a consequence of perturbed LRS1 function, indicating its role as a crown regulator. In conjunction with random forest-based network modeling, these transcriptome analyses predicted that LRS1 controls photoprotection gene expression via an algal HY5 homolog as its prime transcription factor target. CrHY5 binds to T-box elements present in the promoters of these genes and its inactivation in thehit1mutant via CRISPR-Cas9 genome editing, confirmed the regulatory connection between LRS1 and CrHY5, predicted by the network analysis