1. Biomolecular Mass Spectrometry and Proteomics Group, Utrecht Institute for Pharmaceutical Science, Utrecht University, Utrecht 3584 CH, The Netherlands
2. Netherlands Proteomics Center, Padualaan 8, 3584 CH Utrecht, The Netherlands
3. Division of Molecular Oncology and Immunology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands