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F-actin-like ATPase activity in a polymerization-defective mutant yeast actin (V266G/L267G)
1Department of Biochemistry, University of Iowa College of Medicine, Iowa City, IA 52242, USA.
The Journal of Biological Chemistry
|May 1, 2001
Summary
Mutant yeast actin (GG-actin) exhibits ATPase activity similar to polymerized actin (F-actin) without forming stable filaments. Tropomyosin stabilizes these unstable oligomers, restoring polymerization.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Actin polymerization is crucial for cell structure and function.
- Actin's ATPase activity is linked to polymerization dynamics.
- Mutations affecting actin's hydrophobic core can alter its properties.
Purpose of the Study:
- To investigate the ATPase activity and polymerization characteristics of a mutant yeast actin (GG-actin).
- To understand the role of specific hydrophobic residues in actin's function.
- To explore the interaction of tropomyosin with unstable actin oligomers.
Main Methods:
- Monitoring of inorganic phosphate (P(i)) release to assess ATPase activity.
- In vitro polymerization assays with GG-actin under varying conditions (Mg2+, Ca2+).
- Analysis of GG-actin's response to temperature changes and tropomyosin.
Main Results:
- GG-actin displays increased ATPase activity under polymerization conditions, despite lacking stable filament formation.
- Apparent critical concentrations for GG-actin were determined (8 µM for Mg2+, 11 µM for Ca2+).
- GG-actin's ATPase activity is cold-sensitive, and tropomyosin stabilizes unstable GG-actin oligomers, promoting polymerization.
Conclusions:
- GG-actin exhibits F-actin-like ATPase activity via temperature-sensitive, unstable oligomers.
- Tropomyosin's role is to stabilize these oligomers, not necessarily to enhance nucleation.
- Hydrophobic interactions are critical for actin filament stability and ATPase regulation.