1. Structural and Chemical Biology Department, Centro de Investigaciones Biológicas Margarita Salas, CIB-CSIC, Madrid 28040, Spain
2. Center for Cooperative Research in Biosciences (CIC bioGUNE), Basque Research and Technology Alliance (BRTA), Bizkaia Technology Park, Building 800, 48160 Derio, Spain
3. CAI de RMN, Universidad Complutense de Madrid, 28040 Madrid, Spain
4. Ikerbasque, Basque Foundation for Science, 48013 Bilbao, Spain