title: Three-dimensional structure of the complex of skeletal muscle actin and bovine pancreatic DNAse I at 6-A resolution.
abstract: The structure of rabbit skeletal muscle actin complexed with bovine pancreatic DNase I has been determined by x-ray crystallographic methods at 6-A resolution. The analysis was based on a new orthorhombic crystal form, space group P212121, with one complex in the asymmetric unit. Six isomorphous heavy-atom derivatives yielding an overall figure of merit of 0.72 have been used to calculate the electron-density map. Molecular models for actin and DNase I derived from this map have dimensions 67 X 40 X 37 A and 50 X 50 X 40 A, respectively. The actin molecule is elongated and consists of a larger and a smaller domain, each containing density regions resembling a central beta-pleated sheet surrounded by alpha-helices. The highest electron-density peak is found in the cleft between the two domains, perhaps indicating the bound ATP. Observed crystal contacts between actin molecules and a model for the F-actin filament are discussed. Two high-affinity Ca2+-binding sites which also bind Ba2+ have been located at the surface of the DNase I molecule.
mesh_terms: D000199:Actins; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002417:Cattle; D003599:Cytoskeleton / Q000648:ultrastructure; D003850:Deoxyribonuclease I; D003851:Deoxyribonucleases; D004720:Endonucleases; D010179:Pancreas / Q000201:enzymology; D011485:Protein Binding; D011487:Protein Conformation; D011817:Rabbits; D014961:X-Ray Diffraction
chemical_list: D000199:Actins; D003851:Deoxyribonucleases; D004720:Endonucleases; D003850:Deoxyribonuclease I; D002118:Calcium