1. Advanced Biological and Environmental X-ray Facility, Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, Department of Plant and Microbial Biology, University of California, Berkeley, California 94720, Department of Applied Science, University of California, Davis, California 95616, and SPring-8, Japan Synchrotron Radiation Institute, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan