1. The Michael Barber Centre for Collaborative Mass Spectrometry, The School of Chemistry, Manchester Institute for Biotechnology, University of Manchester, Manchester M13 9PL, U.K.
2. Department of Biomedical Engineering and Center for Biological Systems Engineering, Washington University in St. Louis, Campus Box 1097, One Brookings Drive, St. Louis, Missouri 63130, United States
3. Structural Biology, MS 311, Room D1024F, St. Jude Children’s Research Hospital, 262 Danny Thomas Place, Memphis, Tennessee 38105-3678, United States