1. Service de Bioénergétique, Biologie Structurale et Mécanismes, Institut de Biologie et Technologies de Saclay, CNRS URA 2096, CEA Saclay, 91191 Gif-sur-Yvette, France, Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, and Biological Chemistry Department, John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, United Kingdom