P7 Dipolar EPR spectroscopy on membrane embedded transport complexes

Our main objective within this SFB is the application of PELDOR (pulsed electron-electron double resonance) spectroscopy to determine structural changes of membrane transport proteins between their different functional states. PELDOR is based on dipolar interactions between two electron spins and can be used to estimate the distance and orientation of these spin labels to each other. The possible distances range from 1.5 up to 8 nm - which strongly depends on the echo phase memory time.

Our goal is to study several membrane proteins in lipid membranes. However, the phase memory time is often very short in such environments, therefore one of our first goals is to optimize the sample composition that satisfies both the structural integrity of the membrane protein and a sufficient length of the phase memory time to reach the necessary PELDOR quality.

We apply this spectroscopic method to multidrug transporters like LmrA: the aim is to obtain information about structural features and conformational changes that determine drug binding and transport during the ATP cycle. A series of nitroxide spin-labeled mutants along the LmrA transmembrane domain will be prepared by the Glaubitz group. Another collaboration with the group of MacKinnon (Rockefeller, NY) is intended to study several membrane-voltage depending states of KvAP, a tetrameric voltage-dependent potassium ion channel protein. A simpler ion channel KcsA does show for proteins unusually strong restricted orientations of the spin labels and demonstrates the potential of PELDOR spectroscopy. Other transporters (e.g. TBsmr, ABCB9) will be studied in a similar way with magnetic resonance spectroscopic methods, in cooperation with other groups of this SFB.