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Interaction of filamentous actin with isolated liver plasma membranes
Abstract:
Actin-membrane interactions have been studied using purified liver plasma membranes and muscular filamentous actin. Despite the large quantity of endogenous actin present in membranes, exogenous muscular filamentous actin cosediments with membranes after a 30 min centrifugation at 30 000 g. The cosedimentation process is time-dependent and exhibits a complex relationship with actin concentration. The cosedimentation of actin with membranes can be partly explained by gelation as shown by low-shear viscosity and electron microscopy. The characterization of the gelation phenomenon as a function of time, actin and membrane concentrations, ionic strength, temperature and Ca2+ concentration is also presented. Gelation alone cannot however account for the overall cosedimentation data, and a more direct mode of association between actin and the membrane must be envisaged. The analogy that exists between the results obtained with liver plasma membranes and those obtained with other membrane systems suggests that a general mechanism may be involved in the interaction of actin with plasma membranes.
Insights
This study shows that muscular filamentous actin binds to liver plasma membranes, partly through a gelation process. Further direct association mechanisms are proposed for actin-membrane interactions.
Area of Science:
- Cell biology
- Biochemistry
- Biophysics
Background:
- Actin-membrane interactions are crucial for cellular processes.
- Endogenous actin is present in plasma membranes, but its interaction with exogenous actin is not fully understood.
Purpose of the Study:
- To investigate the cosedimentation of muscular filamentous actin with purified liver plasma membranes.
- To characterize the mechanisms underlying actin-membrane association, including gelation.
Main Methods:
- Cosedimentation assays using purified liver plasma membranes and muscular filamentous actin.
- Low-shear viscosity measurements.
- Electron microscopy.
- Characterization of gelation under varying conditions (time, concentrations, ionic strength, temperature, Ca2+).
Main Results:
- Exogenous filamentous actin cosediments with liver plasma membranes.
- Cosedimentation is time-dependent and concentration-dependent.
- Gelation contributes to actin-membrane association, as evidenced by viscosity and microscopy.
- Gelation alone does not fully explain the observed cosedimentation.
Conclusions:
- A direct mode of association between actin and plasma membranes, beyond gelation, is suggested.
- Findings suggest a general mechanism for actin-plasma membrane interactions across different membrane systems.