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Dual effect of filamin on actomyosin ATPase activity
Abstract:
Filamin binds to F-actin and influences the myosin-actin interaction. At relatively low concentrations, filamin activates actomyosin Mg2+-ATPase, whereas higher concentrations of filamin exert an inhibitory effect. Activation of ATPase activity occurs under conditions where a loose meshwork of actin filaments is present and inhibition is associated with the appearance of closely apposed bundles of actin filaments. Maximum activation (about fourfold) of actomyosin ATPase activity by filamin occurs between 30 and 65 mM KCl, at pH 6.5, and at temperatures not less than 30 degrees C. ATPase activation requires higher concentrations of filamin in the presence than in the absence of tropomyosin. Filamin does not activate Mg2+-ATPase activity of acto-subfragment-1 and has only a slight effect on the Mg2+-ATPase of acto-heavy meromyosin, but it inhibits the activity of both these systems under conditions similar to those that inhibit actomyosin ATPase activity.
Insights
Filamin protein modulates actomyosin ATPase activity, activating it at low concentrations and inhibiting it at high concentrations by altering actin filament structure. Optimal activation occurs under specific ionic and temperature conditions.
Area of Science:
- Biochemistry
- Cell Biology
- Muscle Physiology
Background:
- Filamin is a protein that interacts with F-actin.
- It plays a role in regulating the myosin-actin interaction.
- The concentration-dependent effects of filamin on actomyosin Mg2+-ATPase activity are not fully understood.
Purpose of the Study:
- To investigate the dual role of filamin in modulating actomyosin Mg2+-ATPase activity.
- To determine the conditions under which filamin activates or inhibits ATPase activity.
- To explore the influence of actin filament organization on filamin's effects.
Main Methods:
- Biochemical assays measuring actomyosin Mg2+-ATPase activity.
- Varying concentrations of filamin, KCl, and tropomyosin.
- Microscopic observation of actin filament organization.
Main Results:
- Filamin activates actomyosin Mg2+-ATPase at low concentrations and inhibits at high concentrations.
- Activation is linked to loose actin meshworks; inhibition to bundled actin filaments.
- Optimal activation (fourfold) observed at 30-65 mM KCl, pH 6.5, and ≥30°C.
- Tropomyosin influences filamin's activation threshold.
- Filamin inhibits acto-subfragment-1 and acto-heavy meromyosin ATPase activity under similar conditions.
Conclusions:
- Filamin exhibits concentration-dependent regulation of actomyosin ATPase activity.
- Actin filament structure is critical for filamin's regulatory effects.
- Filamin's influence varies depending on the myosin binding partner (myosin II vs. subfragment-1 or heavy meromyosin).