1. Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, United Kingdom
2. Computational Proteomics Unit, Cambridge Centre for Proteomics, University of Cambridge, Cambridge CB2 1QW, United Kingdom
3. School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom
4. MRC Laboratory of Molecular Biology, Cambridge CB2 0QH United Kingdom