title: Crystal structure of the actin-binding region of utrophin reveals a head-to-tail dimer.
abstract: BACKGROUND
  Utrophin is a large multidomain protein that belongs to a superfamily of actin-binding proteins, which includes dystrophin, alpha-actinin, beta-spectrin, fimbrin, filamin and plectin. All the members of this family contain a common actin-binding region at their N termini and perform a wide variety of roles associated with the actin cytoskeleton. Utrophin is the autosomal homologue of dystrophin, the protein defective in the X-linked Duchenne and Becker muscular dystrophies, and upregulation of utrophin has been suggested as a potential therapy for muscular dystrophy patients.
  
  
  RESULTS
  The structure of the actin-binding region of utrophin, consisting of two calponin-homology (CH) domains, has been solved at 3.0 A resolution. It is composed of an antiparallel dimer with each of the monomers being present in an extended dumbell shape and the two CH domains being separated by a long central helix. This extended conformation is in sharp contrast to the compact monomer structure of the N-terminal actin-binding region of fimbrin.
  
  
  CONCLUSIONS
  The crystal structure of the actin-binding region of utrophin suggests that these actin-binding domains may be more flexible than was previously thought and that this flexibility may allow domain reorganisation and play a role in the actin-binding mechanism. Thus utrophin could possibly bind to actin in an extended conformation so that the sites previously identified as being important for actin binding may be directly involved in this interaction.
authors.affiliation: MRC Laboratory of Molecular Biology, Cambridge, UK. n.keep@bbk.ac.uk
authors.forename: N H
authors.initials: NH
authors.lastname: Keep
authors.forename: S J
authors.initials: SJ
authors.lastname: Winder
authors.forename: C A
authors.initials: CA
authors.lastname: Moores
authors.forename: S
authors.initials: S
authors.lastname: Walke
authors.forename: F L
authors.initials: FL
authors.lastname: Norwood
authors.forename: J
authors.initials: J
authors.lastname: Kendrick-Jones
mesh_terms: D000199:Actins / Q000378:metabolism*; D000595:Amino Acid Sequence; D001665:Binding Sites; D018360:Crystallography, X-Ray; D003598:Cytoskeletal Proteins / Q000737:chemistry* / Q000378:metabolism*; D019281:Dimerization; D016189:Dystrophin / Q000737:chemistry / Q000235:genetics; D006801:Humans; D007700:Kinetics; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009136:Muscular Dystrophies / Q000235:genetics / Q000628:therapy; D019906:Nuclear Magnetic Resonance, Biomolecular; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012984:Software; D049411:Utrophin
chemical_list: D000199:Actins; D003598:Cytoskeletal Proteins; D016189:Dystrophin; D008565:Membrane Proteins; D011994:Recombinant Proteins; D049411:Utrophin