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Monomeric Acanthamoeba myosins I support movement in vitro
The Journal of Biological Chemistry
|July 25, 1985
Summary
Acanthamoeba myosins IA and IB are nonfilamentous motor proteins that move on actin cables. Their movement is ATP-dependent and requires heavy chain phosphorylation, demonstrating their role in cellular functions.
Area of Science:
- Biochemistry
- Cell Biology
- Molecular Motors
Background:
- Acanthamoeba myosins IA and IB are characterized by their molecular weights and Stokes radii.
- These myosins exhibit distinct secondary structure compositions: Myosin IA is 22% alpha-helix, 32% beta-structure, and 46% unordered, while Myosin IB is 16% alpha-helix, 46% beta-structure, and 38% unordered.
- Unlike other myosins, both IA and IB remain monomolecular even under conditions that typically induce filament formation.
Purpose of the Study:
- To investigate the biophysical properties and functional capabilities of Acanthamoeba myosins IA and IB.
- To determine if these nonfilamentous myosins can mediate actin-dependent movement.
- To elucidate the requirements for the motor activity of Acanthamoeba myosins IA and IB.
Main Methods:
- Determination of molecular weights, Stokes radii, and frictional ratios for myosins IA and IB.
- Analysis of the secondary structure content (alpha-helix, beta-structure, unordered) of both myosins.
- In vitro motility assays using beads coated with myosin IA or IB on Nitella actin cables.
- Biochemical assays to assess the role of ATP, heavy chain phosphorylation, and myosin I antiserum in motor function and ATPase activity.
Main Results:
- Acanthamoeba myosins IA and IB have molecular weights of 159,000 and 150,000 Da, respectively, with frictional ratios of 1.7.
- Beads coated with myosins IA or IB exhibited unidirectional movement along actin cables, indicating motor function.
- This movement was dependent on ATP and phosphorylation of the myosin I heavy chain, which also correlated with actin-activated Mg2+-ATPase activity.
- Inhibition of motor activity and ATPase activity was observed with myosin I antiserum.
Conclusions:
- Acanthamoeba myosins IA and IB are nonfilamentous, monomolecular myosins capable of supporting actin-dependent movement.
- Their motor function is regulated by ATP and heavy chain phosphorylation, similar to filamentous myosins.
- These findings highlight the functional versatility of nonfilamentous myosins in cellular processes.