1. Cardiovascular Research Institute, University of California, San Francisco, CA 93858-2330, USA.
2. Department of Physiology, University of California, San Francisco, CA 93858-2330, USA.
3. Science Division, Diamond Light Source, Harwell Science and Innovation Campus, Didcot, OX11 0DE, UK.
4. Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA, 15260, USA.
5. Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 93858-2330, USA.
6. Departments of Biochemistry and Biophysics, and Cellular and Molecular Pharmacology, University of California, San Francisco, CA 93858-2330, USA.
7. California Institute for Quantitative Biomedical Research, University of California, San Francisco, CA 93858-2330, USA.
8. Kavli Institute for Fundamental Neuroscience, University of California, San Francisco, CA, 93858-2330, USA.
9. Molecular Biophysics and Integrated Bio-imaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720 USA.