Ultrafast dynamics of biomolecules studied by vibrational spectroscopy on selectively isotope labeled proteins

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Non-covalent interactions like hydrogen bonding and diploar interactions determine all biological processes. Because of its sensitivity and the ability to perform time resolved experiments on timescales from femtoseconds to hours vibrational spectroscopy is an ideal tool to study these protein/protein and protein/cofactor interactions. Interpretation of vibrational spectra of such highly complex biomolecules, however, is usually complicated by strongly overlapping signals leading to an ambigous molecular assignment. We propose to address this bottleneck by a combined biochemical and spectroscopic approach. On the biochemistry side we will establish efficient site specific isotope labeling protocols for both cofactor and protein side chains. The protein samples will be produced in engineered E. coli strains that lack selected amino acid or cofactor biosynthesis genes thus enabling to selectively feed isotope labeled substrates. The labeled protein samples will then be studied by vibrational (infrared and Raman scattering) spectroscopy using state-of-the-art methods with ps (pump-probe) to min (step-scan) time resolution. As a model system we will investigate BLUF (Blue light sensors using FAD) photoreceptor domains. They contain a so far poorly understood flavin cofactor, which is surrounded by a hydrogen bonded network that is reversibly switched within picoseconds after a light flash. Using this model system we want to establish a highly efficient, general method for studying complex biomolecules. To do so we will combine the expertise of two specialized research groups, which have profound experience on the biochemical and spectroscopic study of photoreceptors. This collaboration is intensified by frequent exchange of the biochemists and spectroscopists between the two laboratories.