Research

Structure and function of photosynthetic protein complexes in eukaryotes

Our main interests are the molecular mechanisms for adaptation of the photosynthetic apparatus to changing light condition, whereby we focus on diatoms (Prof. C. Büchel) as well as on higher plants (Dr. L. Dietzel).

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 so-called light reactions of photosynthesis of these organisms is in the focus of our research. Especially their ability to switch from light-harvesting to protection against light 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 antisense or RNAi methods. 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, 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‘).

The structure of the light harvesting protein complexes. The proteins are membrane intrinsic with 3 membrane spanning helices (shown schematically in a) and form complexes of different oligomeric states. Thereby differences exist between different groups of diatoms (b and d), whereas the overall structure of Photosystem I seems to be similar (c).

 

Model of FCPa und FCPb from C. meneghiniana including pigments (adopted from Premvardhan et al 2010) shown as a monomer (side view, a) or trimer (top view, b). Chl a molecules are drawn in green, Chl c in brown, and black and grey Chl a molecules refer to Chls present in FCPb but absent in FCPa. Fucoxanthin shifts in absorption upon protein binding, thus molecules absorbing at slightly shorter wavelengths (blue) or longer wavelengths (red, see also absorption spectra) exist.


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. One of these proteins, CryP, is currently analysed and was found to influence the regulation of light harvesting protein expression.

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 a further project we genetically modify diatoms to increase the triacylglycerid production (pending patent 10 2011 113 283.3).

The projects are embedded in a DFG Research Group (Specific light driven reactions in unicellular model algae, FOR 1261, http://www.uni-jena.de/en/DFG_Research__Group_1261.html) 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“ (http://www.uni-frankfurt.de/se2b), which is co-ordinated by us. In addition close collaboration exist inside (Prof. Wachtveitl, FB14, Prof. Sandmann and Prof. Bode, FB15) und and outside the Goethe University (in the framework of the projects mentioned above).