Structure and function of photosynthetic protein complexes in eukaryotes

The molecular mechanisms of adaptation of the photosynthetic apparatus to changing light conditions are our main interests, whereby we focus on diatoms.

Some of the diatoms studied, Cyclotella meneghiniana (a –d) and Phaeodactylum tricornutum (e and f), REM picture (a and b), light microscopic picture (c and e) and TEM picture (d and f). Bars correspond to 1 µm in (a), (b), (d) and (f) and 2 µm in (c) and (e), respectively.

Regulation of light harvesting in diatoms

Diatoms are unicellular, eukaryotic algae, which are interesting due to the following reasons: they are responsible for about 25% of the world's primary production and are one of the major carbon sinks in the oceans. The regulation of the light reactions of photosynthesis of these organisms is the focus of our research. Especially their ability to switch from light-harvesting to photoprotection is one of the reasons for their big success in the marine environment, despite lacking own means for mobility. Diatoms can be genetically manipulated; thus we use methods for overexpression of tagged proteins or down-regulate the expression of genes by RNAi or CRISPR-Cas. In addition, general biochemical and spectroscopic methods are used to analyse the structure and function of the proteins, and their interaction in protein complexes. To visualise the protein structures we also use electron microscopical methods.
The pigments of diatoms: absorbance spectra of pigments (1 mM in aceton, a) and of one of the light harvesting complexes (FCPa of C. meneghiniana, b).

During the last years we were able to analyse the variety of light harvesting proteins in different groups of diatoms, their association with the photosystems and their function, with special emphasis on the switch from light harvesting to protection. In the framework of several collaborations the excitation energy transfer between pigments, and the special function of one carotenoid in protection was further elucidated. (see ‚Publications'). ‚Publications').
The structure of the light harvesting complexes. The proteins are membrane intrinsic with 3 membrane spanning helices (scheme in a), and constitute different oligomers In (b) the pigment organisation of Chl a (green), Chl c (blue green) and Fucoxanthin (orange) in a trimer is shown (top-view adapted from Gelzinis et al. 2020). Dotted lines surround one monomer each.

Organisation of the light harvesting proteins of T. pseudonana and C. meneghiniana (adopted from Arshad et al. 2021) in Photosystem I (a), Photosystem II (b) and in the free FCP-complexes FCPa and FCPb, (c). Different colors denote FCPs from different protein families.

The role of photoreceptors in light regulation of diatoms

Light is not only used for photosynthesis, but also an important signal in gene regulation received by receptor molecules. In diatoms genes for cryptochromes can be found. Cryptochromes can absorb blue light, and are working as receptors and/or function in DNA repair. We were the first to characterise a so-called “plant-like cryptochrome", CryP. Members of this protein family have meanwhile be found in many phylogenetic groups. CryP is involved in the gene regulation in many ways. At the moment we are elucidating the signal transduction pathway.

Characteristics of CryP. The redox state of the FAD bound depends on the presence of the C-terminal extension (CTE) (a). CryP as a dimer can bind two proteins (b), a protein specific for diatoms and a transcription factor; BolA (adopted from Krischer et al. 2022).

Diatoms in biotechnology

In addition, diatoms are rather interesting in biotechnological research due to their ability to e.g. produce lipids in high amounts and especially lipids containing poly-unsaturated fatty acids. In further projects we genetically modified diatoms to increase the triacylglycerid and/or the omega-3-fatty acid production.

The projects were embedded in a DFG Research Group (Specific light driven reactions in unicellular model algae, FOR 1261) and a Marie Curie Training and Research Network of the EU, “Solar Energy to Biomass – Optimisation of light energy conversion in plants and microalgae- SE2B“ (, which was co-ordinated by us. In addition, close collaboration exist inside und and outside the Goethe University (in the framework of the projects mentioned above).


Plant Cell Phyiology

Prof. Dr. Claudia Büchel

Biocentre, Campus Riedberg
Building 210, Raum 202
Max-von-Laue-Str. 9
60438 Frankfurt am Main

T +49 69 798-29602
F +49 69 798-29600

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Susanne Horst

T +49 69 798-29601

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