1. Department of Molecular Biology and Biotechnology, Krebs Institute for Biomolecular Research, University of Sheffield Firth Court Western Bank Sheffield S10 2TN UK
2. Present address: Avecia Biotechnology, Belasis Avenue Billingham Cleveland TS23 1YN UK
3. Department of Molecular Microbiology, John Innes Centre Colney Lane Norwich NR4 7UH UK
4. Present address: Department of Human Anatomy and Genetics, University of Oxford South Parks Road Oxford OX1 3QX UK
5. ME Müller Institute for Structural Biology, Biozentrum, University of Basel Klingelbergstrasse 50/70 4056 Basel Switzerland