Electron crystallography of ultrathin 3D protein crystals: atomic model with charges.
Membrane proteins and macromolecular complexes often yield crystals too small or too thin for even the modern synchrotron X-ray beam. Electron crystallography could provide a powerful means for structure determination with such undersized crystals, as protein atoms diffract electrons four to five orders of magnitude more strongly than they do X-rays. Furthermore, as electron crystallography yields Coulomb potential maps rather than electron density maps, it could provide a unique method to visualize the charged states of amino acid residues and metals. Here we describe an attempt to develop a methodology for electron crystallography of ultrathin (only a few layers thick) 3D protein crystals and present the Coulomb potential maps at 3.4-Å and 3.2-Å resolution, respectively, obtained from Ca(2+)-ATPase and catalase crystals. These maps demonstrate that it is indeed possible to build atomic models from such crystals and even to determine the charged states of amino acid residues in the Ca(2+)-binding sites of Ca(2+)-ATPase and that of the iron atom in the heme in catalase.
Biostructural Mechanism Laboratory, RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo, Hyogo 679-5148, Japan; Institute of Molecular and Cellular Biosciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan;
Koji
K
Yonekura
Hitachi High-Tech Fielding Corporation, 4-28-8 Yotsuya, Shinjuku-ku, Tokyo, 160-0004, Japan; and.
Kazuyuki
K
Kato
Institute of Molecular and Cellular Biosciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan;
Mitsuo
M
Ogasawara
Institute of Molecular and Cellular Biosciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan; Hitachi High-Technologies Corporation, 1-24-14 Nishi-Shinbashi, Minato-ku, Tokyo, 105-8717, Japan.
Masahiro
M
Tomita
Institute of Molecular and Cellular Biosciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan; ct@iam.u-tokyo.ac.jp.
Chikashi
C
Toyoshima
D000818:Animals; D000252:Calcium-Transporting ATPases / Q000737:chemistry*; D002374:Catalase / Q000737:chemistry*; D002417:Cattle; D018360:Crystallography, X-Ray / Q000379:methods*; D004583:Electrons; D008958:Models, Molecular; D055672:Static Electricity
D002374:Catalase; D000252:Calcium-Transporting ATPases
Ca2+-ATPase; Coulomb potential; catalase; electron crystallography; protein crystal