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Association of a cellular myosin II with anionic phospholipids and the neuronal plasma membrane
1Department of Anatomy and Neurobiology, Medical College of Pennsylvania, Philadelphia 19129.
Abstract:
Myosin II has been observed in close proximity to the neuronal plasma membrane, suggesting the possibility that at least one isoform of neuronal myosin II may be capable of direct association. Here, we demonstrate that a significant fraction (> 30%, saturable around 90%) of brain myosin II, but not myosins from skeletal or cardiac muscle, can bind to lipid vesicles composed of the anionic phospholipid L-alpha-phosphatidyl-L-serine but not with vesicles made from the neutral phospholipid L-alpha-phosphatidylcholine. Binding to lipid vesicles made from L-alpha-phosphatidyl-L-serine is enhanced in the presence of millimolar amounts of free calcium. ATPase activity remains unimpaired after vesicle association. Myosin II was also shown to remain in tight association with purified plasma membranes, even after depletion of actin. The above observations suggest that mechanisms involving membrane-bound myosin II are required to facilitate metazoan cell motility.
Insights
Brain myosin II directly binds to anionic lipids in neuronal membranes, a key step for cell motility. This interaction is calcium-dependent and does not affect myosin
Area of Science:
- Cell Biology
- Neuroscience
- Biochemistry
Background:
- Myosin II is present near neuronal plasma membranes, hinting at direct interactions.
- The specific membrane-binding properties of neuronal myosin II are not well understood.
Purpose of the Study:
- To investigate the direct association of brain myosin II with neuronal membranes.
- To determine the lipid specificity and calcium dependence of this interaction.
Main Methods:
- Lipid vesicle binding assays using anionic (L-alpha-phosphatidyl-L-serine) and neutral (L-alpha-phosphatidylcholine) phospholipids.
- Analysis of myosin II binding to purified plasma membranes.
- Assessment of ATPase activity post-membrane association.
Main Results:
- Brain myosin II selectively binds to anionic lipid vesicles (L-alpha-phosphatidyl-L-serine), but not neutral ones.
- Calcium ions enhance the binding of brain myosin II to anionic lipids.
- Myosin II remains associated with purified plasma membranes even without actin.
- ATPase activity is preserved after membrane binding.
Conclusions:
- Neuronal myosin II directly associates with anionic phospholipids in the plasma membrane.
- This membrane association is calcium-dependent and crucial for cell motility mechanisms.
- Membrane-bound myosin II plays a significant role in facilitating metazoan cell movement.