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Aip1p Dynamics Are Altered by the R256H Mutation in Actin
Published on: July 30, 2014
Functional studies of yeast actin mutants corresponding to human cardiomyopathy mutations
W W Wong1, T C Doyle, P Cheung
1Department of Chemistry and Biochemistry, Molecular Biology Institute, University of California, Los Angeles 90095, USA.
Insights
Distinct actin mutations cause different cardiomyopathies by altering protein function. This study reveals how specific mutations impair actin stability, filament formation, and binding interactions, leading to hypertrophic and dilated cardiomyopathy.
Area of Science:
- Molecular Biology
- Biochemistry
- Cardiovascular Research
Background:
- Cardiomyopathies are a group of diseases affecting the heart muscle.
- Mutations in alpha-cardiac actin are linked to hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM).
- The precise molecular mechanisms underlying these distinct disease phenotypes remain unclear.
Purpose of the Study:
- To investigate the functional consequences of specific alpha-cardiac actin mutations associated with HCM and DCM.
- To elucidate how these mutations affect actin stability, polymerization, and interactions with binding partners.
- To establish structure-function relationships between actin mutations and cardiomyopathy development.
Main Methods:
- Expression and purification of wild-type (WT) and mutant actin proteins in yeast.
- In vitro functional assays including circular dichroism melting experiments and filament formation studies.
- Assessment of yeast cell growth and temperature sensitivity.
- Evaluation of alpha-actinin binding to mutant actin.
Main Results:
- The A331P mutation (HCM) impaired actin function, reducing stability and hampering filament formation, suggesting disrupted actin-actin interactions.
- Yeast strains with the R312H mutation (DCM) exhibited compromised cell viability.
- The E361G mutation (DCM) significantly reduced alpha-actinin binding (threefold decrease) despite normal in vitro motility, indicating impaired force transduction.
Conclusions:
- Actin mutations associated with HCM (A331P) can lead to filament instability and actomyosin dysfunction.
- Actin mutations linked to DCM (R312H, E361G) can compromise cell viability and impair force transduction through altered binding interactions.
- These findings provide molecular insights into the pathogenesis of distinct cardiomyopathies driven by specific actin mutations.
Abstract:
The molecular mechanisms by which different mutations in actin lead to distinct cardiomyopathies are unknown. Here, actin mutants corresponding to alpha-cardiac actin mutations causing hypertrophic cardiomyopathy [(HCM) P164A and A331P] and dilated cardiomyopathy [(DCM) R312H and E361G] were expressed in yeast and purified for in vitro functional studies. While P164A appeared unaltered compared to wild-type (WT) actin, A331P function was impaired. A331P showed reduced stability in circular dichroism melting experiments; its monomer unfolding transition was 10 degrees C lower compared to WT actin. Additionally, in vitro filament formation was hampered, and yeast cell cultures were temperature sensitive, implying perturbations in actin-actin interactions. Filament instability of the A331P mutant actin could lead to actomyosin dysfunction observed in HCM. Yeast strains harboring the R312H mutation did not grow well in culture, suggesting that cell viability is compromised. The E361G substitution is located at an alpha-actinin binding region where the actin filament is anchored. The mutant actin, though unaltered in the in vitro motility and standard actomyosin functions, had a threefold reduction in alpha-actinin binding. This could result in impairment of force-transduction in muscle fibers, and a DCM phenotype.
