title: Crystal structure of the SMC head domain: an ABC ATPase with 900 residues antiparallel coiled-coil inserted.
abstract: SMC (structural maintenance of chromosomes) proteins are large coiled-coil proteins involved in chromosome condensation, sister chromatid cohesion, and DNA double-strand break processing. They share a conserved five-domain architecture with three globular domains separated by two long coiled-coil segments. The coiled-coil segments are antiparallel, bringing the N and C-terminal globular domains together. We have expressed a fusion protein of the N and C-terminal globular domains of Thermotoga maritima SMC in Escherichia coli by replacing the approximately 900 residue coiled-coil and hinge segment with a short peptide linker. The SMC head domain (SMChd) binds and condenses DNA in an ATP-dependent manner. Using selenomethionine-substituted protein and multiple anomalous dispersion phasing, we have solved the crystal structure of the SMChd to 3.1 A resolution. In the monoclinic crystal form, six SMChd molecules form two turns of a helix. The fold of SMChd is closely related to the ATP-binding cassette (ABC) ATPase family of proteins and Rad50, a member of the SMC family involved in DNA double-strand break repair. In SMChd, the ABC ATPase fold is formed by the N and C-terminal domains with the 900 residue coiled-coil and hinge segment inserted in the middle of the fold. The crystal structure of an SMChd confirms that the coiled-coil segments in SMC proteins are anti-parallel and shows how the N and C-terminal domains come together to form an ABC ATPase. Comparison to the structure of the MukB N-terminal domain demonstrates the close relationship between MukB and SMC proteins, and indicates a helix to strand conversion when N and C-terminal parts come together.
authors.affiliation: Laboratory of Molecular Biology, MRC, Hills Road, Cambridge, CB2 2QH, UK. jyl@mrc-lmb.cam.ac.uk
authors.forename: J
authors.initials: J
authors.lastname: Löwe
authors.forename: S C
authors.initials: SC
authors.lastname: Cordell
authors.forename: F
authors.initials: F
authors.lastname: van den Ent
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000235:genetics; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D018797:Cell Cycle Proteins / Q000737:chemistry* / Q000235:genetics; D003460:Crystallization; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics; D016415:Sequence Alignment; D020124:Thermotoga maritima / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D018797:Cell Cycle Proteins; D011993:Recombinant Fusion Proteins; C118650:SMC protein, Bacteria; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases