Our work aims at the molecular understanding of ion transfer within membrane proteins, protein conformational changes, as well as protein-protein interactions.
Oxyrrhisrhodopsin is an algal rhodopsin from the heterotrophic dinoflagellate Oxyrrhys marina. Its high similarity with the proton-pump proteorhodopsin suggests that Oxyrrhisrhodopsin plays a role in the energy-metabolism of this heterotrophic alga. This protein is still uncharacterized by any biochemical or biophysical method.
This project is accomplished in close collaboration with the group of Prof. Ernst Bamberg (MPI for Biophysics, Frankfurt/Main, Germany).
Melanopsin is a G protein-coupled receptor that is present in mammalian retinal ganglion cells and shares high sequence similarity with invertebrate opsins. Behavioral studies on mice demonstrated that melanopsin is responsible for visual functions such as papillary light reflex and circadian photo-entrainment. In spite of numerous physiological experiments, the structure and functional mechanism of melanopsin are still unknown.
This project is accomplished in close collaboration with the groups of Dr. Ramona Schlesinger, Freie Universität Berlin, Department of Physics, Genetic Biophysics, and of Prof. Samer Hattar, John Hopkins University, Department of Biology, Baltimore, USA.
Sensory rhodopsin I:
Sensory rhodopsin I (SRI) from Halobacterium salinarum belongs to the family of seven-transmembrane proteins which carry all-trans retinal as chromophore. SRI signals are detected by the transducer protein HtrI that is intimate complexed with the receptor in the membrane. The communication between proteins is little understood in any organism. In this respect, SRI/HtrI complex has proven as model systems for the elucidation of membrane protein interactions. Thus, the introduction of FT-IR spectroscopy for the investigation of structural changes which ocurr during SRI photoreaction and SRI/HtrI interaction is crucial, since the details on how the transducer protein modulates the photochemical kinetics of SRI are relevant. This project is teamwork with the groups of Dr. Ramona Schlesinger, Freie Universität Berlin, Department of Physics, Genetic Biophysics, and of Prof. Joachim Heberle, Freie Universität Berlin, Department of Physics, Experimental Molecular Biophysics.
Channelrhodopsin-2 (ChR2 ) from the unicellular green alga Chlamydomonas reinhardtii is a light-gated cation channel that controls the photomovement of the cell. The observation that ChR2 depolarizes membranes within a few milliseconds in response to light flashes motivated neuroscientists to use ChR2 as an optogenetic tool for controlling neuronal activity. Our FT-IR difference spectra showed that the non-conductive states of ChR2 exhibit large conformational changes which were interpreted as dynamics of the ion pore. In contrast, the gating mechanism of the conductive states is poorly understood. Thus, we aim at the structural characterization of the conductive states of ChR2 by time-resolved step-scan FT-IR spectroscopy.
This project is teamwork with the groups of Prof. Joachim Heberle (Experimental Molecular Biophysics) and of Dr Ramona Schlesinger (Genetic Biophysics) both at Freie Universität Berlin, Department of Physics, and with the group of Prof. Ernst Bamberg (MPI for Biophysics, Frankfurt/Main, Germany)