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BP: Fachverband Biologische Physik

BP 27: Single Molecule Biophysics

BP 27.9: Talk

Thursday, March 21, 2024, 12:00–12:15, H 0112

Residue Size Dependency of the Geminate Recombination Dynamics of the Biologically Relevant Disulfide Moiety af- ter UV-cleavage investigated by TRXAS — •Jessica Harich — Institute of Nanostructure and Solid State Physics, University of Hamburg and Center for Free-Electron Laser Science, Germany

The tertiary structure of proteins is stabilized by disulfide bonds formed from two spatially adjacent L-cysteinyl residues. These disulfide bridges are prone to UV radiation damage with potentially adverse effects. We employ time resolved X-ray absorption spectroscopy (TRXAS) to observe the UV photochemistry of the natural amino acid dimer L-cystine and the tripeptide Glutathione disulfide in aqueous solution to understand the photochemistry under physiological con- ditions. Furthermore, we have first exciting insights into the UV-photochemistry of the disulfide bridges within the protein hen egg white Lysozyme.

We find that upon UV irradiation, apliphatic disulfides immediately undergo S-S bond cleavage, leading to the formation of two identical thiyl radicals, followed by fast geminate recombination indicating a very effective recombination process for thiyl radicals to the ground state. This process is only possible in condensed phases and its speed increases with chain length. Our results show that L-cystine already captures the essence of the ultrafast photochemistry of the disulfide bridge, but that the size of the residue adjacent to the disulfide bonds has a strong influence on the immediate recombination dynamics of the photoproducts.

Keywords: UV-photocleavage; femtosecond X-ray absorption spectroscopy; liquid phase; protein disulfide bonds