Calmodulin structure refined at 1.7 A resolution.
We have determined and refined the crystal structure of a recombinant calmodulin at 1.7 A resolution. The structure was determined by molecular replacement, using the 2.2 A published native bovine brain structure as the starting model. The final crystallographic R-factor, using 14,469 reflections in the 10.0 to 1.7 A range with structure factors exceeding 0.5 sigma, is 0.216. Bond lengths and bond angle distances have root-mean-square deviations from ideal values of 0.009 A and 0.032 A, respectively. The final model consists of 1279 non-hydrogen atoms, including four calcium ions, 1130 protein atoms, including three Asp118 side-chain atoms in double conformation, 139 water molecules and one ethanol molecule. The electron densities for residues 1 to 4 and 148 of calmodulin are poorly defined, and not included in our model, except for main-chain atoms of residue 4. The calmodulin structure from our crystals is very similar to the earlier 2.2 A structure described by Babu and coworkers with a root-mean-square deviation of 0.36 A. Calmodulin remains a dumb-bell-shaped molecule, with similar lobes and connected by a central alpha-helix. Each lobe contains three alpha-helices and two Ca2+ binding EF hand loops, with a short antiparallel beta-sheet between adjacent EF hand loops and one non-EF hand loop. There are some differences in the structure of the central helix. The crystal packing is extensively studied, and facile crystal growth along the z-axis of the triclinic crystals is explained. Herein, we describe hydrogen bonding in the various secondary structure elements and hydration of calmodulin.
Chattopadhyaya
R
R
Howard Hughes Medical Institute, Baylor College of Medicine, Houston, TX 77030.
Meador
W E
WE
Means
A R
AR
Quiocho
F A
FA
D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002147:Calmodulin / Q000737:chemistry* / Q000302:isolation & purification / Q000502:physiology; D006860:Hydrogen Bonding; D008024:Ligands; D008958:Models, Molecular; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000648:ultrastructure; D014867:Water / Q000737:chemistry / Q000378:metabolism; D014961:X-Ray Diffraction
D002147:Calmodulin; D008024:Ligands; D011994:Recombinant Proteins; D014867:Water; D002118:Calcium