1. Molecular Biology Institute, University of California, Los Angeles, CA 90095, USA.
2. Mass Spectrometry Facility, Department of Biochemistry, School of Medicine, Loma Linda University, Loma Linda, CA 92350, USA.
3. Department of Biological Chemistry, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA.
4. Department of Microbiology, Immunology, and Molecular Genetics, University of California, Los Angeles, CA 90095, USA.