1. Department of Chemistry, University of Michigan, 930 North University Avenue, 48109-1055, Ann Arbor, MI, USA
2. Current Address: Proteome Exploration Laboratory, Division of Biology, California Institute of Technology, 91125, Pasadena, CA, USA
3. Current Address: MS Proteomics at The European Institute of Oncology, via Adamello 16, 20139, Milan, Italy