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Published on: July 15, 2014
The molecular mechanism of muscle dysfunction associated with the R133W mutation in Tpm2.2
Yurii S Borovikov1, Olga E Karpicheva1, Stanislava V Avrova1
1Institute of Cytology, Russian Academy of Sciences, 4 Tikhoretsky Av., St. Petersburg, 194064, Russia.
Abstract:
Ghost muscle fibres reconstituted with myosin heads labeled with the fluorescent probe 1,5-IAEDANS were used for analysis of muscle fibre dysfunction associated with the R133W mutation in β-tropomyosin (Tpm2.2). By using polarized microscopy, we showed that at high Ca2+ the R133W mutation in both αβ-Tpm heterodimers and ββ-Tpm homodimers decreases the amount of the myosin heads strongly bound to F-actin and the number of switched-on actin monomers, with this effect being stronger for ββ-Tpm. This mutation also inhibits the shifting of the R133W-Tpm strands towards the open position and the efficiency of the cross-bridge work. At low Ca2+, the amount of the strongly bound myosin heads is lower for R133W-Tpms than for WT-Tpms which may contribute to a low myofilament Ca2+-sensitivity of the R133W-Tpms. It is concluded that freezing of the mutant αβ- or ββ-Tpm close to the blocked position inhibits the strong binding of the cross-bridges and the switching on of actin monomers which may be the reason for muscle weakness associated with the R133W mutation in β-tropomyosin. The use of reagents that activate myosin may be appropriate to restore muscle function in patients with the R133W mutation.
Insights
The R133W mutation in beta-tropomyosin impairs muscle function by reducing myosin-actin binding and actin activation. Activating myosin may restore muscle function in affected individuals.
Area of Science:
- Muscle physiology
- Molecular biology
- Biochemistry
Background:
- The R133W mutation in beta-tropomyosin (Tpm2.2) is associated with muscle fiber dysfunction.
- Understanding the molecular mechanisms underlying this mutation is crucial for developing therapeutic strategies.
Purpose of the Study:
- To analyze the impact of the R133W mutation in beta-tropomyosin on muscle fiber function at the molecular level.
- To investigate the effects of the mutation on myosin-actin interactions and myofilament calcium sensitivity.
Main Methods:
- Utilized ghost muscle fibers reconstituted with fluorescently labeled myosin heads.
- Employed polarized microscopy to analyze myosin-actin binding and actin monomer activation.
- Investigated the influence of calcium concentrations on these interactions.
Main Results:
- The R133W mutation significantly reduces strong myosin-actin binding and actin monomer activation at high calcium levels.
- This effect is more pronounced in beta-beta tropomyosin homodimers compared to alpha-beta heterodimers.
- The mutation inhibits tropomyosin strand shifting and cross-bridge work efficiency, leading to reduced myofilament calcium sensitivity.
Conclusions:
- The R133W mutation hinders cross-bridge binding and actin activation, potentially causing muscle weakness.
- Freezing of mutant tropomyosin near a blocked position disrupts essential muscle contraction mechanisms.
- Myosin-activating reagents show promise for restoring muscle function in patients with this mutation.
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