This project focuses on the optimization of orthogonal spin labeling methodologies and state-of-the-art setups for pulsed dipolar EPR spectroscopy to study the interaction network of Bcl-2 proteins leading to cell death under physiological conditions. Relevant for the project is the development of a three-spin orthogonal labeling scheme for simultaneous detection of interactions among multiple proteins in the same sample using nitroxide-, Cu- and Ln-based labels. We will screen the suitability of nitroxide labels resistant to reducing conditions, and functionalized metal and lanthanide chelators. A trisNTA-based Gd-label for His-tagged proteins will also be developed. This work will help establishing EPR as a technique to retrieve high resolution site-specific structural information on Bcl-2 proteins at the onset of apoptosis on isolated mitochondria, and will be extended towards in-cell EPR, exploring and optimizing methods to internalize spin-labeled proteins into mammalian cells.