Our research group is focusing on the elucidation of functioning of membrane proteins and subsequent signal transduction chains. To investigate proteins with biophysical methods the protein has to be available in quantitative amounts. We are using homologous and heterologous expression systems to produce the target proteins in sufficient amounts. To modify protein sequences we use molecular biological methods which lead to site-specific mutagenesis on DNA level. Such mutagenized protein molecules are investigated by spectroscopic methods as FTIR, Raman and EPR spectroscopy as well as used for crystallization to analyze by x-ray diffraction.