Microfilament organization and actin-binding proteins

Microfilaments are dynamic and are modulated by a large number of actin binding proteins (ABP). A large number of intracellular proteins bind to actin filaments. These range from proteins whose only function is to bind actin to those with well-characterized cellular functions in addition to the ability to bind actin. ABPs are traditionally classified according to their actin binding function. Many types of actin filament cross-linking proteins that hold the filaments in orthogonal or bundled arrays to form viscous gels have been characterized. Other proteins exist that bind and block the ends of filaments. A smaller number of actin monomer binding proteins have been identified and these are thought to sequester a pool of unpolymerized actin within cells. This pool is presumably released to form new actin structures upon suitable stimulation, such as a chemoattractant. Details of individual ABPs are necessary, but a major challenge is to establish computer aided models to predict and explain the complex behavior and properties of microfilaments and multi-ABP complexes in vitro and in vivo.