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Proteolytic substructure of brain myosin
Abstract:
Individual bovine brain myosin molecules visualized by electron microscopy consist of two globular heads and a fibrous tail, like myosin molecules from other sources. Brain myosin, however, showed much lower solubility at moderate to high ionic strength (0.2 to 0.4 M KCl) than gizzard myosin, and the filaments formed at low ionic strength in the presence of Mg2+ were fairly resistant to low concentrations of ATP, by which gizzard myosin filaments were completely solubilized. Brain myosin was digested with low concentrations of papain, alpha-chymotrypsin, or trypsin, and the fragmentation patterns were analyzed by means of polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, sedimentation at low ionic strength, and electron microscopy of the fragments produced. The results indicate that all of the proteases cleave the myosin molecule primarily at sites located in the neck or in the head close to the neck, suggesting that the brain myosin molecule contains a hinge region or an open peptide stretch around these sites. The differences as well as the similarities between the proteolytic fragmentation patterns of brain myosin and other myosins are discussed.
Insights
Bovine brain myosin exhibits unique solubility and ATP resistance compared to gizzard myosin. Protease digestion reveals cleavage sites in the brain myosin head or neck region, suggesting a flexible hinge.
Area of Science:
- Biochemistry
- Molecular Biology
- Structural Biology
Background:
- Myosin, a motor protein, is crucial for muscle contraction and cellular motility.
- Bovine brain myosin shares structural similarities with other myosins, featuring globular heads and a fibrous tail.
- Understanding myosin variants like brain myosin provides insights into diverse cellular functions.
Purpose of the Study:
- To characterize the biochemical and structural properties of bovine brain myosin.
- To compare the solubility and filament stability of brain myosin with gizzard myosin.
- To investigate the proteolytic fragmentation patterns of brain myosin to identify structural features.
Main Methods:
- Electron microscopy for visualizing myosin structure.
- Solubility assays at varying ionic strengths (0.2-0.4 M KCl).
- Proteolytic digestion using papain, alpha-chymotrypsin, and trypsin, followed by SDS-PAGE, sedimentation, and electron microscopy.
Main Results:
- Bovine brain myosin demonstrated significantly lower solubility in moderate to high ionic strength buffers compared to gizzard myosin.
- Brain myosin filaments showed resistance to low ATP concentrations, unlike gizzard myosin filaments.
- Protease digestion consistently cleaved brain myosin near the head-tail junction, indicating a flexible hinge or open region.
Conclusions:
- Bovine brain myosin possesses distinct biochemical properties influencing its function.
- The identified cleavage sites suggest a flexible hinge region in brain myosin, potentially impacting its motor activity.
- Comparative analysis highlights structural and functional diversity among myosin isoforms.