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Self-association of chicken gizzard filamin and heavy merofilamin
Abstract:
Filamin is a high molecular weight (subunit Mr 250 000) actin-binding protein isolated from smooth muscle. The protein forms a gel when mixed with solutions of F-actin. A proteolytic fragment of filamin, heavy merofilamin (subunit Mr 240 000), generated by the action of Ca2+-activated protease binds to actin but does not produce gelation. We have studied the self-association properties of filamin and heavy merofilamin by direct examination in the electron microscope and by equilibrium sedimentation distribution studies in the ultracentrifuge. Filamin self-associates reversibly to form dimers; the free energy of dimerization is approximately 7 kcal/mol. Further association to form tetramer and multimer appears to be irreversible. Warming of filamin solutions accelerates aggregation. Heavy merofilamin does not appear to self-associate but is entirely monomeric. These studies suggest that filamin produces gelation of F-actin by binding to actin and then self-associating to cross-link actin filaments into a gel.
Insights
Filamin, an actin-binding protein, self-associates to form dimers and multimers, enabling it to cross-link actin filaments. This self-association is crucial for the gelation of F-actin by filamin.
Area of Science:
- Biochemistry
- Cell Biology
- Structural Biology
Background:
- Filamin is a high molecular weight actin-binding protein found in smooth muscle.
- Filamin induces gelation of F-actin, a process not replicated by its proteolytic fragment, heavy merofilamin.
- Understanding filamin's self-association is key to elucidating its role in F-actin cross-linking.
Purpose of the Study:
- To investigate the self-association properties of filamin and heavy merofilamin.
- To determine the mechanism by which filamin induces F-actin gelation.
Main Methods:
- Electron microscopy for direct visualization of protein structures.
- Equilibrium sedimentation distribution studies in the ultracentrifuge to analyze self-association.
- Proteolytic digestion to generate heavy merofilamin.
Main Results:
- Filamin reversibly self-associates into dimers with a free energy of dimerization of approximately 7 kcal/mol.
- Further association of filamin into tetramers and multimers appears irreversible and is accelerated by warming.
- Heavy merofilamin remains monomeric and does not exhibit self-association.
Conclusions:
- Filamin's ability to self-associate into dimers and higher-order multimers is essential for its function.
- Filamin likely produces F-actin gelation by binding to actin and subsequently self-associating to cross-link actin filaments.
- Heavy merofilamin's lack of self-association explains its inability to cause F-actin gelation.