1. University of California, Irvine, Department of Biomedical Engineering, Irvine, California 92697, United States
2. University of Helsinki, Finland and Minerva Foundation Institute for Medical Research, Department of Anatomy and Research Programs Unit, Faculty of Medicine, Helsinki 00290, Finland
3. University of Geneva, NCCR Chemical Biology, Department of Biochemistry, CH-1211 Geneva, Switzerland
4. University of California, Irvine, Department of Chemistry, Irvine, California 92697, United States