1. Department of Crystallography and Structural Biology, Instituto de Química-Física “Rocasolano”, CSIC, Serrano 119, 28006 Madrid, Spain
2. Department of Chemistry and Biochemistry, University of Notre Dame, Nieuwland Hall of Science, Notre Dame, Indiana 46556, United States
3. Instituto de Biología Molecular de Barcelona, CSIC, Baldiri Reixach 13, 08028 barcelona, Spain, and ICREA (Institucio Catalana de Recerca y Estudis Avançats)