Functional characterisation of different fucoxanthin chlorophyll proteins (FCP) in diatoms

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The aim of this project is to understand the excitation energy transport in the antenna complexes of diatoms, fucoxanthin-chlorophyll proteins (FCPs), the possible protective function of FCPs and the macromolecular organisation of the FCP proteins around the photosystems. Despite the fact that several groups of FCPs can be distinguished on the level of genes, usually only one or two main antenna complexes are purified and biochemical and spectroscopic data on distinct FCPs are scarce. Thus, little is known about possible functional heterogeneities of these different polypeptides. In order to characterise single antenna proteins we want to transform diatoms with different FCP genes modified by addition of tags in order to be able to separate specific FCPs against the background of all related proteins. Additionally, putative pigment binding sites will be mutated to obtain FCPs with different pigmentation. The genetically engineered FCPs should then allow for a detailed biochemical and spectroscopic characterisation. Special emphasis will be on the role of diatoxanthin in fluorescence quenching depending on its localisation in the different FCPs. The studies on mutant FCPs will be accompanied by studies on the arrangement of the different FCP proteins with respect to the different photosystems. Additionally, using the His-tags to label FCPs for electron microscopy will allow to specifically locate the FCPs inside supercomplexes of the photosystems.