Myopathy-inducing mutation H40Y in ACTA1 hampers actin filament structure and function

Abstract

In humans, more than 200 missense mutations have been identified in the ACTA1 gene. The exact molecular mechanisms by which, these particular mutations become toxic and lead to muscle weakness and myopathies remain obscure. To address this, here, we performed a molecular dynamics simulation, and we used a broad range of biophysical assays to determine how the lethal and myopathy-related H40Y amino acid substitution in actin affects the structure, stability, and function of this protein. Interestingly, our results showed that H40Y severely disrupts the DNase I-binding-loop structure and actin filaments. In addition, we observed that normal and mutant actin monomers are likely to form distinctive homopolymers, with mutant filaments being very stiff, and not supporting proper myosin binding. These phenomena underlie the toxicity of H40Y and may be considered as important triggering factors for the contractile dysfunction, muscle weakness and disease phenotype seen in patients.

Nebulin stiffens the thin filament and augments cross-bridge interaction in skeletal muscle

“…To address whether the thin filament regulatory proteins tropomyosin and troponin are influenced by nebulin, we studied the off-meridional 2ALL (tropomyosin) ( 21 ) and meridional TN3 (troponin) ( 28 ) reflections (for their locations see Fig. 1 C and D ).…”

“…Small spacing changes in the higher-order meridional reflections in response to muscle activation denote the axial extensibility of actin and myosin subunits and are therefore sensitive indicators of myofilament ultrastructure ( 15 – 18 ). Additionally, whereas higher-order actin layer lines represent the geometry of the thin filament helix ( 19 ), its lower-order layer lines reflect the movement of the regulatory proteins on the thin filament ( 20 , 21 ). We provide evidence that nebulin stiffens the thin filament by acting on its actin subunits, fine-adjusts its helix, and is required for optimal tropomyosin/troponin movement on the thin filament.…”

Molecular Consequences of the Myopathy-Related D286G Mutation on Actin Function

“…The arrays were then transferred to the skinning solution and stored at -20°C. Approximately 80 arrays were mounted (10 arrays per mouse – four knock-in and four wild-type mice – corresponding to approximately 2,400 attached fibers) (Ochala et al, 2015; Chan et al, 2016).…”

“…It is then unclear how the remaining defects interfere with cross-bridge functioning (Nowak et al, 2013). In the present study, based on one of our previous studies (Chan et al, 2016) and on computational simulations (Kojima et al, 1994; Wakabayashi et al, 1994; Miller et al, 2010) we aimed to test the hypothesis that one of the major triggering factors of muscle weakness would be altered actin filament structure. To verify this, we applied a unique combination of molecular dynamics (MD) simulation and ex vivo experiments (small-angle x-ray scattering).…”

Impairments in contractility and cytoskeletal organisation cause nuclear defects in nemaline myopathy

“…These mutations result in weakness at the contractile level, while other cellular pathological hallmarks include dense accumulations of proteins known as nemaline rods, arrested muscle fibre growth, impaired fibre type differentiation, and disarray of contractile filaments 1 . However, the underlying mechanisms behind these features remain uncertain, even though the mutations affecting thin filament structure and function are likely to be involved [2][3][4][5][6][7][8][9] . In the present study, we aimed to acquire a clearer understanding of muscle fibre dysfunction in NM by specifically studying nuclei and the related cortical cytoskeleton.…”