1 Leibniz Institute of Experimental Virology and Universität Hamburg, Department of Structural Cell Biology of Viruses, Centre for Structural Systems Biology (CSSB), Notkestr. 85, 22607 Hamburg, Germany; Division of Structural Biology, Wellcome Centre for Human Genetics, University of Oxford, Roosevelt Drive, Headington, Oxford, OX3 7BN, UK. Electronic address: Kay.Gruenewald@cssb-hamburg.de.
2 Hannover Medical School, Institute of Virology, Structural Virology Group, Carl Neuberg-Str. 1, D-30625 Hannover, Germany. Electronic address: krey.thomas@mh-hannover.de.