1. Biomolecular Mass Spectrometry and Proteomics Group, Bijvoet Center for Biomolecular Research and Utrecht Institute for Chemistry, Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht, The Netherlands, and Gene Center Munich and Center for Integrated Protein Science CiPSM, Department of Chemistry and Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, 81377 Munich, Germany