1. Centre de RMN à Très Hauts Champs, Université de Lyon (CNRS/ENS Lyon/UCB Lyon 1), 69100 Villeurbanne, France, Biotechnology Laboratory, IRCCS Fondazione Policlinico San Matteo, Pavia, Italy, Department of Biochemistry, University of Pavia, Italy, and Department of Biomolecular Sciences and Biotechnology, University of Milano, Italy