Actin binding protein

Fig. 1. The GP Ib-IX-V complex. The complex consists of seven transmembrane polypeptides denoted GP Iba (mol wt 145,000), GP IbP (mol wt 24,000), GPIX (mol wt 17,000) and GP V (mol wt 82,000), in a stoichiometry of 2 2 2 1. The hatched region represents the plasma membrane. The area above the hatched region represents the extracellular space that below represents the cytoplasm. The complex is a major attachment site between the plasma membrane and the cytoskeleton. Two molecules associated with the cytoplasmic domain are depicted a 14-3-3 dimer, which may mediate intracellular signaling, and actin-binding protein, which connects the complex to the cortical cytoskeleton and fixes its position and influences its function.

By binding to F-actin, actin binding proteins (ABPs) stabilize F-actin or regulate its turnover. Known ABPs are proteins such as a-actinin, talin, tensin, filamin, nexilin, fimbrin, and vinculin. 

Actin Binding Proteins Actin Filaments Action Potential... 

Nonmuscle Actin-Binding Proteins Drugs Affecting Actin Polymerization Patterns of Arrangement of Actin Filaments in Animal Cells Three-Dimensional Networks The Microtrabecular Lattice... 

The cytoskeleton also contains different accessory proteins, which, in accordance with their affinities and functions, are designated as microtubule-associated proteins (MAPs), actin-binding proteins (ABPs), intermediate-filament-associated proteins (IFAPs), and myosin-binding proteins. This chapter is focused on those parts of the cytoskeleton that are composed of microfilaments and microtubules and their associated proteins. The subject of intermediate filaments is dealt with in detail in Volume 2. 

More than 50 proteins have been discovered in the cytosol of nonmuscle cells that bind to actin and affect the assembly and disassembly of actin filaments or the cross-linking of actin filaments with each other, with other filamentous components of the cytoskeleton, or with the plasma membrane. Collectively, these are known as actin-binding proteins (ABPs). Their mechanisms of actions are complex and are subject to regulation by specific binding affinities to actin and other molecules, cooperation or competition with other ABPs, local changes in the concentrations of ions in the cytosol, and physical forces (Way and Weeds, 1990). Classifications of ABPs have been proposed that are based on their site of binding to actin and on their molecular structure and function (Pollard and Cooper, 1986 Herrmann, 1989 Pollard et al., 1994). These include the following ... 

The diversity of these subcellular actin structures is remarkable and appears to be determined by the interactions of many actin-binding proteins (ABPs) as well as by changes in the concentrations of intracellular signaling molecules such as Ca and cAMP, by small GTP-binding proteins, and by signals arising from mechanical stress. Approximately 50% of the actin molecules in most animal cells are unpolymerized subunits in the cytosolic pool and exist in a state of dynamic equilibrium with labile F-actin filamentous structures (i.e., new structures are formed while existing structures are renewed) (Hall, 1994). 

Pollard, T.D. Cooper, J.R. (1986). Actin and actin-binding proteins. A critical evaluation of mechanisms and functions. Ann. Rev. Biochem. 55, 987-1035. 

Pollard, T.D., Almo, S., Quirk, S., Vinson, V., Lattman, E.E. (1994). Structure of actin binding proteins Insights about function at atomic resolution. Ann. Rev. Cell Biol. 10,207-249. 

Tollman, R.L., Morton, D.J., Clarke, F.M. (1989). A common theme in the amino acid sequences of actin and many actin-binding proteins. Trends Biochem. Sci. 14, 130-133. 

Actin Polymerization Regulation by Divalent Metal Ion and Nucleotide Bindings ATP Hydrolysis and Actin Binding Proteins... 

The Role of Myosins in Cell Locomotion The Role of Actin-Binding Proteins in Cell Locomotion The Transduction of Extracellular Motility Signals to the Cytoskeleton Lipid Flow and Cell Locomotion The Role of Cell Locomotion in Metastasis Intracellular Motility Microtubule-Based Intracellular Motility... 

Microfilament immobilized through interaction with the bulk of the cell cortex via actin binding proteins. 

Figure 4. The Brownian ratchet model of lamellar protrusion (Peskin et al., 1993). According to this hypothesis, the distance between the plasma membrane (PM) and the filament end fluctuates randomly. At a point in time when the PM is most distant from the filament end, a new monomer is able to add on. Consequently, the PM is no longer able to return to its former position since the filament is now longer. The filament cannot be pushed backwards by the returning PM as it is locked into the mass of the cell cortex by actin binding proteins. In this way, the PM is permitted to diffuse only in an outward direction. The maximum force which a single filament can exert (the stalling force) is related to the thermal energy of the actin monomer by kinetic theory according to the following equation ...

The Role of Actin-Binding Proteins in Cell Locomotion... 

Cunningham, C.C., Gorlin, J.B., Kwiatowski, D.J., Hartwig, J.H., Janmey, P.A., Byers, R., Stossel, T.P. (1992). Actin-binding protein requirement for cortical stability efficient locomotion. Science, 255,325-327. 

Maciver, S.K. (1994). Actin binding proteins. In Encylopaedia of Molecular Biology (Kendiew, J., Lawrence, E., eds.), pp. 7-14. Blackwell, Oxford. 

Maciver, S.K. (1995). Actin organization and actin-binding proteins. In Treatise on the Cytoskeleton (Hesketh, J.E., Pryme, I.F., eds.), JAI Press Inc., Greenwich. 

Another actin binding protein, the large 100 kDa a-actinin, crosslinks actin filaments together at the dense bodies and near the points of actin filament attachment to the cell membranes, a-actinin is also associated with still another actin binding protein, vinculin, which may stabilize both the Z-line like dense bodies and the membrane attachments. 

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