1. Faculty of Biology, Bielefeld University , Postfach 100131, 33501 Bielefeld , Germany
2. Faculty of Mathematics, University of Vienna , Oskar-Morgenstern-Platz 1, 1090 Vienna , Austria
3. Claude Bernard University Lyon 1, Department of Biology , 43 bd du 11 novembre 1918, 69622 Villeurbanne cedex , France
4. Max Perutz Labs, University of Vienna , Dr.-Bohrgasse 9, 1030 Vienna , Austria