Abstract

Proteins perform vital functions in the living organisms. They need to fold into their final tertiary structure in order to function properly. However, knowing the static tertiary structure of a protein is not enough to understand how it functions since proteins are not rigid bodies. The fact that the proteins go through structural fluctuations has to be taken into account in studying these complex biomolecules. Optical techniques, such as spectral hole burning, can be used in studying the dynamics of proteins. However, most proteins must be doped with dye molecules as probes since most of the proteins do not absorb light in visible region. Pigment-protein complexes involved in photosynthesis are good model systems for studying protein dynamics since the pigment molecules are embedded in these proteins naturally. Understanding the dynamics of proteins involved in photosynthesis and the way they function is important also from the perspective of photosynthesis and renewable energy research. The focus of this seminar is on the low-temperature dynamics and the barrier distributions on the energy landscape of Cytochrome b6f Protein Complex.
Qualitatively, the distributions of barriers between protein sub-states involved in the light-induced conformational changes (i.e. - Non-Photochemical Hole Burning (NPHB)) are close to glass-like, and not to Gaussian. Spectral dynamics of Cytochrome b6f manifesting in NPHB experiments appears to be independent of the deuteration of the buffer/glycerol glassy matrix containing the protein. Proton tunneling in the water/glycerol solvent environment can be excluded as the origin of the observed NPHB and recovery dynamics. Entities involved in the light-induced conformational changes are characterized by md^2 = 2.7-3.6 . 10^-46 kg.m^2. Evidence is presented for excitation energy transfer between chlorophyll molecules of the adjacent monomers. The magnitude of the dipole-dipole coupling deduced from the FLN spectra is in good agreement with the structural data, indicating that explored protein was intact.