Actin-filament capping protein

ACTIN-BASED BACTERIAL MOTILITY ACTIN ASSEMBLY ASSAYS ACTIN ASSEMBLY KINETICS ACTIN FILAMENT CAPPING PROTEIN ACTIN FILAMENT SEVERING PROTEIN... 

ACTIN FILAMENT CAPPING PROTEIN Actin cross-linking/bundling,... 

Maun, NA., Speicher, D.W., EMNubile, M.J. and Southwick, F.S. (1996). Purification and properties of a Ca -independent barbed-end actin filament capping protein, CapZ, from human polymorphonuclear leukocytes. Biochem. 35, 3518-3524. 

Certain proteins can specifically bind to either the barbed or pointed ends of actin filaments. Capping the filaments in this way prevents, or retards, any further elongation or depolymerization of monomers from that end. 

Bear, J.E., Svitkina, T.M., Krause, M.et al. (2002). Antagonism between EnaAT SP proteins and actin filament capping regulates fibroblast motility. Cell 109, 509-521. 

MTs extend from the centrosome throughout the cytoplasm to the plasma membrane, where they are stabilized by caps. Sliding along the MTs, kinesin and dynein motors transport their cargoes between the center and the periphery of the cell. MTs present in the axons of neur ons are extended not only by addition of heterodimers to the plus ends but also by use of short MTs that initiate in the centrosome. Their axonal transport is mediated by dynein motors that are passively moved along actin filaments. Once formed in the axon, MTs serve as tracks for the fast axonal transport, i.e. the movement of membranous organelles and membrane proteins to the nerve ending. 

Barbed-end-capping proteins (gelsolin and villin, 95 kD) attach to this specific end of the actin filament and inhibit the further addition of actin molecules. 

Pointed-end-capping proteins are acumentin (65 kD), spectrin (220-260 kD), and p-actinin (37 kD). They also regulate the length of actin filaments. 

Stress fibers are parallel bundles of actin filaments that develop in the cytoplasm of fibroblasts from the cortical actin network in response to mechanical tension. These often bind to the plasma membrane at focal contacts and, through transmembrane linker glycoproteins, to the extracellular matrix. Thus, actin filaments of stress fibers indirectly Join to the inner face of the plasma membrane through molecular assemblies of attachment proteins, which include an actin-capping protein, a-actinin, vinculin, and talin (Small, 1988). 

Figure 2 The actin-ADP-ribosylating toxins, (a) Molecular mode of action. The actin-ADP-ribosylating toxins covalently transfer an ADP-ribose moiety from NAD+ onto Arg177 of G-actin in the cytosol of targeted cells. Mono-ADP-ribosylated G-actin acts as a capping protein and inhibits the assembly of nonmodified actin into filaments. Thus, actin polymerization is blocked at the fast-growing ends of actin filaments (plus or barbed ends) but not at the slow growing ends (minus or pointed ends). This effect ultimately increases the critical concentration necessary for actin polymerization and tends to depolymerize F-actin. Finally, all actin within an intoxicated cell becomes trapped as ADP-ribosylated G-actin.

Abstract Gelsolin is a calcium-activated actin filament severing and capping protein found in... 

Barkalow, K., W. Witke, D.J. Kwiatkowski, and J.H. Hartwig. 1996. Coordinated regulation of platelet actin filament barbed ends by gelsolin and capping protein. J Cell Biol. 134 389-99. 

---