Biochemistry Information Research Center, National Institute of Advanced Industrial Science and Technology, Ibaragi 305-8566, Japan; telephone, þ81-298-61-5562; fax, þ81-298-61-6478; e-mail, ti- sato@aist.go.jp. R.S.: School of Physiology and Pharmacology, Bristol Heart Institute and Centre for Nanoscience and Quantum Information, University of Bristol, Bristol BS8 1TD, United King- dom; telephone, þ44-117-331-1450; fax, þ41-117-331-2288; e-mail, R.Sitsapesan@bristol.ac.uk. Author Contributions E.V., K.M., and M.N. contributed equally to this work. Funding Sources This work was supported in part by research grants from the Japan Society for the Promotion of Science, the Ministry of Education, Culture, Sports, Science and Technology, the Japan New Energy and Industrial Technology Development Organiza- tion, the British Heart Foundation, the Astellas Foundation, the Mochida Memorial Foundation, the Kanae Foundation, the Daiichi-Sankyo Foundation of Life Science, and the Takeda Science Foundation. ’ ACKNOWLEDGMENT We thank S. Aoki and M. Mio for technical assistance. ’ ABBREVIATIONS 3D, three-dimensional; DDM, n-dodecyl β-D-maltoside; ER, endoplasmic reticulum; EM, electron microscopy; FSC, Fourier shell correlation; mAb, monoclonal antibody; MG23, mitsugumin 23; SR, sarcoplasmic reticulum ’ REFERENCES (1) Berridge, M. J. (2002) The endoplasmic reticulum: A multi- functional signaling organelle. Cell Calcium 32, 235–249. (2) MacLennan, D. H., Abu-Abed, M., and Kang, C.-H. 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