Berlin 2008 – scientific programme

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BP: Fachverband Biologische Physik

BP 26: Posters II

BP 26.27: Poster

Thursday, February 28, 2008, 17:00–19:30, Poster A

Single-molecule Spectroscopy on Phytochromes — •Jana B Nieder, Marc Brecht, and Robert Bittl — Fachbereich Physik, Freie Universität Berlin, Arnimalle 14, 14195 Berlin, Germany

Phytochromes are red light sensitive photoreceptors controlling flowering, shade avoidance and germination in plants. Their cofactor biliverdin is a linear tetrapyrroles whos conformation is strongly affected by the protein environment. The tight binding by the protein surrounding is the basis for the metastable PR and PFR conformational states. The switching between these isomeric states is reversibly triggered by Red and Far Red light.

Physical properties of the interaction between the pigment and its protein surrounding are accessible by single-molecule spectroscopy at low temperatures . Under low temperature conditions major protein rearrangements are inhibited and the phytochromes are trapped in the dark stable state (here PR). The fluorescence emission of single Agp1 molecules (phytochrome from Agrobacterium tumefaciens) shows marked time dependence. The pigment-protein interaction causes intensity and spectral changes. This spectral fine-tuning is observed by comparison of signals from different molecules and within time-dependent spectra of individual Agp1 molecules. For some of the analysed Agp1 molecules narrow lines in the vibronic energy range could be resolved. The spectral fine-tuning affects all vibrational lines simultaneously. For these molecules the vibrational energies can directly be extracted. In this work detection of vibrational information of single chromophores in their natural protein environment is achieved.