title: Structure of calmodulin refined at 2.2 A resolution.
abstract: The crystal structure of mammalian calmodulin has been refined at 2.2 A (1 A = 0.1 nm) resolution using a restrained least-squares method. The final crystallographic R-factor, based on 6685 reflections in the range 2.2 A less than or equal to d less than or equal to 5.0 A with intensities exceeding 2.5 sigma, is 0.175. Bond lengths and bond angles in the molecule have root-mean-square deviations from ideal values of 0.016 A and 1.7 degrees, respectively. The refined model includes residues 5 to 147, four Ca2+ and 69 water molecules per molecule of calmodulin. The electron density for residues 1 to 4 and 148 is poorly defined, and they are not included in the model. The molecule is shaped somewhat like a dumbbell, with an overall length of 65 A; the two lobes are connected by a seven-turn alpha-helix. Prominent secondary structural features include seven alpha-helices, four Ca2+-binding loops, and two short, double-stranded antiparallel beta-sheets between pairs of adjacent Ca2+-binding loops. The four Ca2+-binding domains in calmodulin have a typical EF hand conformation (helix-loop-helix) and are similar to those described in other Ca2+-binding proteins. The X-ray structure determination of calmodulin shows a large hydrophobic cleft in each half of the molecule. These hydrophobic regions probably represent the sites of interaction with many of the pharmacological agents known to bind to calmodulin.
authors.affiliation: Department of Pathology, University of Alabama, Birmingham 35294.
authors.forename: Y S
authors.initials: YS
authors.lastname: Babu
authors.forename: C E
authors.initials: CE
authors.lastname: Bugg
authors.forename: W J
authors.initials: WJ
authors.lastname: Cook
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium; D002147:Calmodulin; D002417:Cattle; D008239:Lysine; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D014867:Water; D014961:X-Ray Diffraction
chemical_list: D002147:Calmodulin; D014867:Water; D008239:Lysine; D002118:Calcium