Medical Faculty of the Humboldt University, (Charité) Institute of Biochemistry, Monbijoustr. 2A, Berlin D-10117, Germany. dietmann@ebi.ac.uk|Medical Faculty of the Humboldt University, (Charité) Institute of Biochemistry, Monbijoustr. 2A, Berlin D-10117, Germany. dietmann@ebi.ac.uk