title: The polyproline site in hinge 2 influences the functional capacity of truncated dystrophins.
abstract: Mutations in dystrophin can lead to Duchenne muscular dystrophy or the more mild form of the disease, Becker muscular dystrophy. The hinge 3 region in the rod domain of dystrophin is particularly prone to deletion mutations. In-frame deletions of hinge 3 are predicted to lead to BMD, however the severity of disease can vary considerably. Here we performed extensive structure-function analyses of truncated dystrophins with modified hinges and spectrin-like repeats in mdx mice. We found that the polyproline site in hinge 2 profoundly influences the functional capacity of a microdystrophin(DeltaR4-R23/DeltaCT) with a large deletion in the hinge 3 region. Inclusion of polyproline in microdystrophin(DeltaR4-R23/DeltaCT) led to small myofibers (12% smaller than wild-type), Achilles myotendinous disruption, ringed fibers, and aberrant neuromuscular junctions in the mdx gastrocnemius muscles. Replacing hinge 2 of microdystrophin(DeltaR4-R23/DeltaCT) with hinge 3 significantly improved the functional capacity to prevent muscle degeneration, increase muscle fiber area, and maintain the junctions. We conclude that the rigid alpha-helical structure of the polyproline site significantly impairs the functional capacity of truncated dystrophins to maintain appropriate connections between the cytoskeleton and extracellular matrix.
authors.affiliation: Department of Neurology, Senator Paul D Wellstone Muscular Dystrophy Cooperative Research Center, University of Washington, Seattle, Washington, United States of America.
authors.forename: Glen B
authors.initials: GB
authors.lastname: Banks
authors.forename: Luke M
authors.initials: LM
authors.lastname: Judge
authors.forename: James M
authors.initials: JM
authors.lastname: Allen
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Chamberlain
mesh_terms: D000818:Animals; D016189:Dystrophin / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D009154:Mutation; D010455:Peptides / Q000737:chemistry / Q000502:physiology*
chemical_list: D016189:Dystrophin; D010455:Peptides; C011083:polyproline