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The filamins: properties and functions.

Canadian Journal of Biochemistry and Cell Biology = Revue Canadienne De Biochimie Et Biologie Cellulaire

|June 1, 1985

Summary

Filamins are proteins that cross-link actin filaments. Their concentration and flexibility influence the formation of actin networks or bundles within cells.

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Area of Science:

Biochemistry
Cell Biology
Biophysics

Background:

Filamins are high molecular weight proteins known to bind actin.
They are composed of two subunits and can cross-link actin filaments.
Their role in organizing cellular actin structures is under investigation.

Purpose of the Study:

To investigate the in vitro cross-linking of actin filaments by filamin.
To analyze network formation using polymer theory and relate it to filamin concentration and actin filament length.
To explore the potential role of filamin concentration in determining actin network versus bundle formation.

Main Methods:

In vitro experiments mixing actin and filamin at varying concentrations.
Analysis of gelation using Flory's theory.
Measurement of critical gelation concentration and its dependence on actin and filamin parameters.

Main Results:

Filamin forms three-dimensional actin networks in vitro, with gelation occurring at a critical concentration.
Critical gelation concentration is inversely proportional to actin filament length.
Measured critical concentrations were higher than predicted, and filamin's length and flexibility facilitate network formation at low molar ratios, promoting bundles at higher ratios.

Conclusions:

Filamin's properties enable efficient cross-linking of actin filaments into networks and bundles.
Filamin concentration relative to actin is a key factor in dictating whether networks or bundles form.
Other cellular factors like competing actin-binding proteins and phosphorylation may modulate filamin's function.

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