title: Missense mutations in dystrophin that trigger muscular dystrophy decrease protein stability and lead to cross-beta aggregates.
abstract: A deficiency of functional dystrophin protein in muscle cells causes muscular dystrophy (MD). More than 50% of missense mutations that trigger the disease occur in the N-terminal actin binding domain (N-ABD or ABD1). We examined the effect of four disease-causing mutations--L54R, A168D, A171P, and Y231N--on the structural and biophysical properties of isolated N-ABD. Our results indicate that N-ABD is a monomeric, well-folded alpha-helical protein in solution, as is evident from its alpha-helical circular dichroism spectrum, blue shift of the native state tryptophan fluorescence, well-dispersed amide crosspeaks in 2D NMR (15)N-(1)H HSQC fingerprint region, and rotational correlation time calculated from NMR longitudinal (T(1)) and transverse (T(2)) relaxation experiments. Compared to WT, three mutants--L54R, A168D, and A171P--show a decreased alpha-helicity and do not show a cooperative sigmoidal melt with temperature, indicating that these mutations exist in a wide range of conformations or in a "molten globule" state. In contrast, Y231N has an alpha-helical content similar to WT and shows a cooperative sigmoidal temperature melt but with a decreased stability. All four mutants experience serious misfolding and aggregation. FT-IR, circular dichroism, increase in thioflavin T fluorescence, and the congo red spectral shift and birefringence show that these aggregates contain intermolecular cross-beta structure similar to that found in amyloid diseases. These results indicate that disease-causing mutants affect N-ABD structure by decreasing its thermodynamic stability and increasing its misfolding, thereby decreasing the net functional dystrophin concentration.
authors.affiliation: Department of Pharmaceutical Sciences, Center for Pharmaceutical Biotechnology, School of Pharmacy, Aurora, CO 80045, USA.
authors.forename: Surinder M
authors.initials: SM
authors.lastname: Singh
authors.forename: Narsimulu
authors.initials: N
authors.lastname: Kongari
authors.forename: Javier
authors.initials: J
authors.lastname: Cabello-Villegas
authors.forename: Krishna M G
authors.initials: KM
authors.lastname: Mallela
mesh_terms: D055592:Biophysical Phenomena; D016189:Dystrophin / Q000737:chemistry* / Q000172:deficiency / Q000235:genetics* / Q000648:ultrastructure; D006801:Humans; D066298:In Vitro Techniques; D046529:Microscopy, Electron, Transmission; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000737:chemistry; D009136:Muscular Dystrophies / Q000209:etiology / Q000235:genetics* / Q000378:metabolism*; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000648:ultrastructure; D020125:Mutation, Missense; D017510:Protein Folding; D055550:Protein Stability; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000648:ultrastructure; D013816:Thermodynamics
chemical_list: D016189:Dystrophin; D046912:Multiprotein Complexes; D050505:Mutant Proteins; D011994:Recombinant Proteins