Probing nucleation, cutting and capping of actin filaments

Gaertner, Andrea; Ruhnau, Klaus; Schröer, Elke; Selve, Norma; Wanger, Michael; Wegner, Albrecht

doi:10.1007/bf01739852

Cited by 19 publications

(10 citation statements)

References 63 publications

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“…The sigmoidal curve with an initial lag phase reflects all signs of cooperativity during actin assembly under potymerirntion conditions. This effect disappears in the presence of talin, as was noticed also for other nucleating proteins [17]. In the presence of talin at a 1: 1 molar ratio to actin, polymerization starts immediately without an apparent lag phase with a 2-fold increase in fluorescence before reaching a steady-state in approx.…”

Section: Fluorescence Measurementssupporting

confidence: 65%

Talin binds to actin and promotes filament nucleation

et al. 1991

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Platelet talin binds to actin in vitro and hence is an actin binding protein. By four different non-interfering assay conditions (fluorescence. Ruorescence recovery after photobleaching, (FRAP). dynamic light scattering and DNase-I inhibition) we show that talin promotes filament nucleation, raises the filament number concentration and increases the net rate of actin polymerization but has no inhibitory effect on filament elongation.Binding of talin to actin occurs at a maximal molar ratio of I :3 as determined by fluorescencetitration under G-buffer conditions. The overall binding constant was T 0.25 FM.

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Section: Fluorescence Measurementssupporting

confidence: 65%

Talin binds to actin and promotes filament nucleation

et al. 1991

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“…Insertin has almost no effect on the critical monomer concentration of actin, in contrast fo capping proteins which increase the critical concentration of treadmilling actin filaments by blocking monomer consumption af the barbed ends and not interfering with monomer production af the pointed ends (Tellam & Frieden, 1982;Harris & Weeds, 1983;Kurth et al, 1983;Wegner & Isenberg, 1983;Hosoya & Mabuchi, 1984;Lees et al, 1984;Walsh et al, 1984;Cou› Korn, 1985;Janmey et al, 1985;Wanger & Wegner, 1985;Rickard & Sheterline, 1986;Selve & Wegner, 1986a;Southwick & DiNubile, 1986;Wegner & Aktories, 1988;Gaertner et al, 1989). Thus, insertin is not a simple capping protein which permits actin polymerization between dissociation and reassociation of the capping protein.…”

Section: Introductionmentioning

confidence: 96%

Mechanism of the insertion of actin monomers between the barbed ends of actin filaments and barbed end-bound insertin

Gaertner

Wegner

1991

J Muscle Res Cell Motil

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Insertin, a protein purified from chicken gizzard smooth muscle, has been shown to retard but not to inhibit actin polymerization at the barbed ends of actin filaments. This effect has been explained by a model in which insertin remains bound to the barbed ends of actin filaments and new actin molecules are inserted into filaments between the barbed ends and barbed end-bound insertin molecules. In this paper we discuss the mechanism of the insertion reaction on a molecular level. A number of simple models were devised and were judged by their agreement with available experimental data. In one class of models insertin was assumed to dissociate from filament ends and to re-associate with the ends. Actin monomers would then bind to a filament end between a dissociation and an association reaction of insertin. In one of the two proposed models in this class insertin binds to an ATP-containing terminal subunit with higher affinity than to an ADP-containing terminal subunit. Dissociation of insertin is brought about by ATP hydrolysis at the terminal filament subunit. Insertion was then thought to re-associate with a filament end following binding of an ATP-containing actin monomer to the filament end. In the other of the two models' insertin was assumed to occur in two conformations which bind to filament ends with different affinities. Association and dissociation of insertin is caused by interconversion between the two forms of insertin. Both models turned out to be incompatible with experimental data. All types of models in which retardation of actin polymerization is brought about by dissociation and re-association of insertin with filament ends can be excluded by a common argument. As 10 nM insertin retards polymerization of 2 microns monomeric actin with maximal efficiency, the rate constant of binding of insertin to a filament end must be considerably higher (greater than 2 microM/10 nM = 200-fold). As the rate of association of actin with a barbed end is almost diffusion-controlled, assembly of insertin with a filament end would have to exceed the rate of a diffusion-controlled reaction. In the other class of models it was assumed that insertin remains permanently bound to filament ends during association or dissociation of an actin molecule and to move towards the terminal subunit of filaments. These models are compatible with experimental data. Thus, models are favoured where insertin remains bound to filament ends during polymerization and depolymerization of actin.

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“…The latter effect is hot catalytic but depends on a stoichiometric interaction of these proteins with actin. These three properties greatly influence the dynamics of actin filament formation (see Pollard & Cooper, 1986;Gaertner et al, 1989;for reviews). As far as their interactions with actin are concemed, brevin and gelsolin behave similarly (see Discussion).…”

Section: Introductionmentioning

confidence: 99%

The action of brevin, an F-actin severing protein, on the mechanical properties and ATPase activity of skinned smooth muscle

Gailly

Lejeune

Capony

et al. 1990

J Muscle Res Cell Motil

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Brevin is a protein which regulates the actin gel-sol transformation: it severs F-actin filaments into shorter ones. This action is Ca-dependent and is prevented by tropomyosin. We tested the effect of brevin on isometric contractions of skinned smooth muscle (taenia coli) and noted a dramatic loss of tension that possibly reflects some F-actin fragmentation. This effect is tentatively attributed to a partial loss of tropomyosin in the skinning procedure. We also studied the effect of brevin on unloaded shortenings of skinned preparations: thin bundles and enzymatically dissociated cells. We observed a marked increase of the velocity of shortening in the presence of brevin. This effect cannot be attributed to an increased ATPase activity as the latter is slightly reduced in the presence of brevin. We interpret this result as reflecting a decrease in internal resistance to movement, possibly by solation of an actin-filamin domain.

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Probing nucleation, cutting and capping of actin filaments

Cited by 19 publications

References 63 publications

Talin binds to actin and promotes filament nucleation

Talin binds to actin and promotes filament nucleation

Mechanism of the insertion of actin monomers between the barbed ends of actin filaments and barbed end-bound insertin

The action of brevin, an F-actin severing protein, on the mechanical properties and ATPase activity of skinned smooth muscle

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