Sabrina Pospich1, Stefan Raunser2. 1. Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany. 2. Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany. stefan.raunser@mpi-dortmund.mpg.de.