title: Mutations in repeating structural motifs of tropomyosin cause gain of function in skeletal muscle myopathy patients.
abstract: The congenital myopathies include a wide spectrum of clinically, histologically and genetically variable neuromuscular disorders many of which are caused by mutations in genes for sarcomeric proteins. Some congenital myopathy patients have a hypercontractile phenotype. Recent functional studies demonstrated that ACTA1 K326N and TPM2 ΔK7 mutations were associated with hypercontractility that could be explained by increased myofibrillar Ca(2+) sensitivity. A recent structure of the complex of actin and tropomyosin in the relaxed state showed that both these mutations are located in the actin-tropomyosin interface. Tropomyosin is an elongated molecule with a 7-fold repeated motif of around 40 amino acids corresponding to the 7 actin monomers it interacts with. Actin binds to tropomyosin electrostatically at two points, through Asp25 and through a cluster of amino acids that includes Lys326, mutated in the gain-of-function mutation. Asp25 interacts with tropomyosin K6, next to K7 that was mutated in the other gain-of-function mutation. We identified four tropomyosin motifs interacting with Asp25 (K6-K7, K48-K49, R90-R91 and R167-K168) and three E-E/D-K/R motifs interacting with Lys326 (E139, E181 and E218), and we predicted that the known skeletal myopathy mutations ΔK7, ΔK49, R91G, ΔE139, K168E and E181K would cause a gain of function. Tests by an in vitro motility assay confirmed that these mutations increased Ca(2+) sensitivity, while mutations not in these motifs (R167H, R244G) decreased Ca(2+) sensitivity. The work reported here explains the molecular mechanism for 6 out of 49 known disease-causing mutations in the TPM2 and TPM3 genes, derived from structural data of the actin-tropomyosin interface.
authors.affiliation: NHLI, Imperial College London, London, W12 0NN, UK.
authors.forename: Steven
authors.initials: S
authors.lastname: Marston
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Memo
authors.forename: Andrew
authors.initials: A
authors.lastname: Messer
authors.forename: Maria
authors.initials: M
authors.lastname: Papadaki
authors.forename: Kristen
authors.initials: K
authors.lastname: Nowak
authors.forename: Elyshia
authors.initials: E
authors.lastname: McNamara
authors.forename: Royston
authors.initials: R
authors.lastname: Ong
authors.forename: Mohammed
authors.initials: M
authors.lastname: El-Mezgueldi
authors.forename: Xiaochuan
authors.initials: X
authors.lastname: Li
authors.forename: William
authors.initials: W
authors.lastname: Lehman
mesh_terms: D000199:Actins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D001665:Binding Sites; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009119:Muscle Contraction / Q000235:genetics; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000473:pathology; D009135:Muscular Diseases / Q000151:congenital / Q000235:genetics* / Q000378:metabolism*; D009154:Mutation; D011485:Protein Binding; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs / Q000235:genetics*; D014335:Tropomyosin / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*
chemical_list: D000199:Actins; D014335:Tropomyosin