1. Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
2. Physics Department, University of Genoa, via Dodecaneso 33, 16146 Genoa, Italy
3. Molecular Microbiology and Structural Biochemistry, UMR 5086, CNRS and University of Lyon, Lyon, France