Actin-binding proteins--regulators of cell architecture and motility

Numerous actin-binding proteins from a variety of cell types have been described. Here I attempt to correlate the properties and functions of some of these. Three major classes have been identified: (1) cross-linking proteins which form filament bundles or isotropic gels; (2) proteins which cap filament ends and nucleate the polymerization of G-actin (many of these also sever actin filaments); (3) proteins which bind to G-actin and stabilize the monomer pool. Some of the proteins described here combine the properties of more than one class and the activities of many of them are regulated by changes in Ca2+ ion concentration.