Actin Stability

Halpain, S., Hipolito, A., Saffer, L. (1998). Regulation of F-actin stability in dendritic spines by glutamate receptors and calci-neurin. J. Neurosci. 18 9835-44. 

Bertazzon, A. Tian, G.H. Lamblin, A. Tsong, T.Y Enthalpic and entropic contributions to actin stability Calorimetry, circular dichroism, and fluorescence study and effects of calcium. Biochem. 1990, 29, 291—298. 

Saito, S., Feng, J., Kira, A., Kobayashi, J., and Ohizumi, Y. (2004) Amphidinolide H, a novel type of actin-stabilizing agent isolated from dinoflagellate. Biochem. Biophys. Res. Commun., 320, 961-965. 

Posey, S.C. and Bierer, B.F. (1999) Actin stabilization by jasplakinolide enhances apoptosis induced by cytokine deprivation. J. Biol. Chem., 274, 4259 265. 

Wriggers and Schulten, 1997b] Wriggers, W., and Schulten, K. Stability and dynamics of G-actin Back door water diffusion and behavior of a subdomain 3/4 loop. Biophys. J. 73 (1997b) 624-639... 

The C-C distance in CaC2 is close to that in ethyne (120.5 pm) and it has been suggested that the observed increase in the lanthanoid and actin-oid carbides results from a partial localization of the supernumerary electron in the antibonding orbital of the ethynide ion [C=C] (see p. 932). The effect is noticeably less in the sesquicarbides than in the dicarbides. The compounds EuC2 and YbC2 differ in their lattice parameters and hydrolysis behaviour from the other LnC2 and this may be related to the relative stability of Eu and Yb (p. 1237). 

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. 

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. 

Phalloidin and phallacidin are cyclic peptides from the mushroom Amanita phalloides that stabilize F-actin. Phalloidin binds to residues 114-118 of an actin protomere and blocks nucleotide exchange without interfering with nucleotide hydrolysis. It enhances the rate of nucleation as well as that of elongation. It slowly penetrates the cell membrane and is used for immunocytochemical localization of F-actin. 

In contrast, jasplakinolide, a cyclodepsipeptide from the marine sponge Jaspis johnstoni, rapidly penetrates the cell membrane. It competes with phalloidin for F-actin binding and has a dissociation constant of approximately 15 nM. It induces actin polymerization and stabilizes pre-existing actin filaments. Dolastatin 11, a depsipeptide from the mollusk Dolabella auricu-laria, induces F-actin polymerization. Its binding site differs from that of phalloidin or jasplakinolide. 

Muscle contraction is initiated by a signal from a motor nerve. This triggers an action potential, which is propagated along the muscle plasma membrane to the T-tubule system and the sarcotubular reticulum, where a sudden large electrically excited release of Ca " into the cytosol occurs. Accessory proteins closely associated with actin (troponins T, I, and C) together with tropomyosin mediate the Ca -dependent motor command within the sarcomere. Other accessory proteins (titin, nebulin, myomesin, etc.) serve to provide the myofibril with both stability... 

Polymer growth J(c) showed nonlinear monomer concentration dependence in the presence of ATP (Carrier et al., 1984), while in the presence of ADP, the plot of J(c) versus monomer concentration for actin was a straight line, as expected for reversible polymerization. The data imply that newly incorporated subunits dissociate from the filament at a slower rate than internal ADP-subunits in other words, (a) the effect of nucleotide hydrolysis is to decrease the stability of the polymer by increasing k and (b) nucleotide hydrolysis is uncoupled from polymerization and occurs in a step that follows incorporation of a ATP-subunit in the polymer. Newly incorporated, slowly dissociating, terminal ATP-subunits form a stable cap at the ends of F-actin filaments. 

Pj release occurs at a relatively apparent slow rate (kobs = 0.005 s" ), so that the transient intermediate F-ADP-Pj in which P is non-covalently bound, has a life time of 2-3 minutes (Carlier and Pantaloni, 1986 Carlier, 1987). While the y-phosphate cleavage step is irreversible as assessed by 0 exchange studies (Carlier et al., 1987), the release of Pi is reversible. Binding of H2PO4 (Kp 10 M) causes the stabilization of actin filaments and the rate of filament growth varies linearly with the concentration of actin monomer in the presence of Pi (Carlier and Pantaloni, 1988). Therefore, Pi release appears as the elementary step responsible for the destabilization of actin-actin interactions in the filament. 

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. 

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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