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Off the beaten path:
Scientists in Freiburg have discovered new transfer paths for electrons


In the development of materials for energy production and distribution, knowledge of molecular processes in electrical charge transfer is fundamental. Research groups of Prof. Dr. Stefan Weber and Prof. Dr. Thorsten Koslowski at the Institute for Physical Chemistry of the Albert-Ludwigs-University Freiburg once more discovered that nature provides interesting templates for long-range electron transfer. They recently published their results in the renowned journal Angewandte Chemie International Edition. In collaboration with Dr. Kenichi Hitomi and Prof. Dr. Elizabeth D. Getzoff of Scripps Research Institute in La Jolla/USA the physico chemists studied proteins from the photolyase/cryptochrome family. These proteins perform a range of different tasks although their topologies are very similar. Photolyases are photoactive DNA repair enzymes, whereas cryptochromes are involved in a number of blue-light photoreception processes ranging from the regulation of circadian rhythms to helping migratory birds to orient themselves along the Earth's magnetic field. All members of the protein family share a cascade of three amino acids that forms a pathway from the protein surface to its core, along which electrons can “hop” upon photoexcitation.

When studying cyanobacterial cryptochrome using time-resolved electron paramagnetic resonance, the charge carriers, however, did not follow the usual electron channel despite the presence of the amino acid cascade known from the other members of the family. Instead, the cascade was used only partially, eventually branching to a non-conserved neighboring amino acid, even though the electrons had to then cover a much longer distance, see Figure.

 

et von tryptophantriad zu fad

 

With the help of theoretical analyses the scientists were able to describe and thereby understand the protein’s unexpected behavior: The orientation of the amino acids has a stronger influence on electron-transfer efficiency than previously expected, and a more  favorable stacking of the amino acid "stepping stones" can compensate for the longer distance. Hence, evident structural similarity does not necessarily lead to identical photochemical behavior. To "understand" the protein, one clearly needs to look closer.

 

Till Biskup, Kenichi Hitomi, Elizabeth D. Getzoff, Sebastian Krapf, Thorsten Koslowski, Erik Schleicher and Stefan Weber, "Unexpected electron transfer in cryptochrome identified by time-resolved EPR spectroscopy", Angewandte Chemie International Edition 50 (2011) 12647–12651, http://dx.doi.org/10.1002/anie.201104321

Till Biskup, Kenichi Hitomi, Elizabeth D. Getzoff, Sebastian Krapf, Thorsten Koslowski, Erik Schleicher and Stefan Weber, "Identifikation unerwarteter Elektronentransferpfade im Cryptochrom durch zeitaufgelöste Elektronenspinresonanz-Spektroskopie", Angewandte Chemie 123 (2011) 12858–12862, http://dx.doi.org/10.1002/ange.201104321

 

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