European Molecular Biology Laboratory, Meyerhofstr, 1, 69012 Heidelberg, Germany. francesca.ciccarelli@embl.de|European Molecular Biology Laboratory, Meyerhofstr, 1, 69012 Heidelberg, Germany. francesca.ciccarelli@embl.de|European Molecular Biology Laboratory, Meyerhofstr, 1, 69012 Heidelberg, Germany. francesca.ciccarelli@embl.de