1. European Molecular Biology Laboratory, c/o DESY, Notkestrasse 85, D-22603 Hamburg, Germany, Department of Chemistry, University of York, Heslington, York, YO10 5DD, United Kingdom, Laboratorium voor Eiwitbiochemie en Eiwitengineering, University of Gent, Ledeganckstraat 35, 9000 Gent, Belgium, and Department of Agro-Environmental Science and Technology, University of Bologna, Viale Berti Pichat 10 I-40127 Bologna, Italy