Cofilin (ADF) Affects Lateral Contacts in F-actin

Bobkov, Andrey A.; Mühlrád, András; Shvetsov, Alexander; Benchaar, Sabrina A.; Scoville, Damon; Almo, Steven C.; Reisler, Emil

doi:10.1016/j.jmb.2004.01.014

Cited by 56 publications

(68 citation statements)

References 41 publications

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“…14,[20][21][22]33 Cofilin binding leads to the reorganization of subdomain 2, 9-11 and disrupts (longitudinal and lateral) filament subunit contacts. [11][12][13]34,35 It is, therefore, likely that the overall reduction in filament stiffness associated with cofilin binding arises from changes in the filament elasticity (E) and geometry (I) achieved by modulating the strength and redistribution of the intra-and intersubunit bonds.…”

Section: Resultsmentioning

confidence: 99%

“…4) and twisting 14 mechanics (Table 1) indicates that cofilin binding disrupts stabilizing contacts between filament subunits and/or enhances their conformational dynamics, both of which have been documented extensively for the cofilin-actin filament interaction. [9][10][11][12][13][14]35 We favor a mechanism in which the cofilin-linked changes in filament bending and twisting mechanics (Table 1) are mediated largely through the reorganization of actin subdomain 2, since the conformation of this region influences the subunit longitudinal contacts and filament flexibility, 33 and is modulated by cofilin binding. [9][10][11] Molecular dynamics simulations 22 indicate that filament lateral contacts are also dependent on the actin subdomain 2 conformation.…”

Section: Discussionmentioning

confidence: 99%

“…Structural and biochemical analysis demonstrates that cofilin alters the filament subunit tilt 7 and increases the filament helical twist, 8 increases the disorder of actin subdomain 2 9 and the DNase-binding loop, 10 disrupts the subdomain 1 to 2 interface of adjacent subunits along the long pitch helix, 11 and weakens stabilizing lateral contacts. 12,13 Cofilin binding lowers the actin filament torsional stiffness, so cofilin-decorated filaments twist more easily than native filaments. 14 The surface tethering-dependence of severing efficiency suggests that filament flexibility plays a critical role in severing by cofilin, 6 and implies that changes in the flexibility contribute to cofilin-mediated destabilization and severing.…”

Section: Introductionmentioning

confidence: 99%

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Cofilin Increases the Bending Flexibility of Actin Filaments: Implications for Severing and Cell Mechanics

McCullough

Blanchoin

Martiel

et al. 2008

Journal of Molecular Biology

210

254

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We determined the flexural (bending) rigidities of actin and cofilactin filaments from a cosine correlation function analysis of their thermally driven, two-dimensional fluctuations in shape. The persistence length of actin filaments is 9.8 µm, corresponding to a flexural rigidity of 0.040 pN µm 2 . Cofilin binding lowers the persistence length ∼5-fold to a value of 2.2 µm and the filament flexural rigidity to 0.0091 pN µm 2 . That cofilin-decorated filaments are more flexible than native filaments despite an increased mass indicates that cofilin binding weakens and redistributes stabilizing subunit interactions of filaments. We favor a mechanism in which the increased flexibility of cofilin-decorated filaments results from the linked dissociation of filament-stabilizing ions and reorganization of actin subdomain 2 and as a consequence promotes severing due to a mechanical asymmetry. Knowledge of the effects of cofilin on actin filament bending mechanics, together with our previous analysis of torsional stiffness, provide a quantitative measure of the mechanical changes in actin filaments associated with cofilin binding, and suggest that the overall mechanical and forceproducing properties of cells can be modulated by cofilin activity.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Cofilin Increases the Bending Flexibility of Actin Filaments: Implications for Severing and Cell Mechanics

McCullough

Blanchoin

Martiel

et al. 2008

Journal of Molecular Biology

210

254

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Section: Molecular Biology Of the Cell 1224mentioning

confidence: 99%

“…The lateral flanks of the frontal region of the lamellipodium may be the least accessible for diffusion of available phalloidin, explaining the even lower speckle intensity observed there compared with the central part. Another cause for reduced rhodaminephalloidin label in the vicinity of the leading edge may be the competition for actin binding between phalloidin and ADF/cofilin (Bobkov et al, 2004), which is abundant in this region of the cell (Svitkina and Borisy, 1999).To equalize the intensity of phalloidin speckles throughout the cell, the images were processed with the Flatten Background filter in MetaMorph software (size parameter 4 pixels). Also, this procedure largely reduced diffuse out-offocus fluorescence in the cell body, revealing bright features in the substrate plane.…”

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confidence: 99%

Tracking Retrograde Flow in Keratocytes: News from the Front

Vallotton

Danuser

Bohnet

et al. 2005

MBoC

130

111

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Actin assembly at the leading edge of the cell is believed to drive protrusion, whereas membrane resistance and contractile forces result in retrograde flow of the assembled actin network away from the edge. Thus, cell motion and shape changes are expected to depend on the balance of actin assembly and retrograde flow. This idea, however, has been undermined by the reported absence of flow in one of the most spectacular models of cell locomotion, fish epidermal keratocytes. Here, we use enhanced phase contrast and fluorescent speckle microscopy and particle tracking to analyze the motion of the actin network in keratocyte lamellipodia. We have detected retrograde flow throughout the lamellipodium at velocities of 1-3 m/min and analyzed its organization and relation to the cell motion during both unobstructed, persistent migration and events of cell collision. Freely moving cells exhibited a graded flow velocity increasing toward the sides of the lamellipodium. In colliding cells, the velocity decreased markedly at the site of collision, with striking alteration of flow in other lamellipodium regions. Our findings support the universality of the flow phenomenon and indicate that the maintenance of keratocyte shape during locomotion depends on the regulation of both retrograde flow and actin polymerization. INTRODUCTIONThe lamellipodium of motile cells is formed of a dense network of branched actin filaments (F-actin) polymerizing in the direction of cell movement. Network assembly at the leading edge is thought to generate the forces that push the plasma membrane forward (Theriot and Mitchison, 1991;Mogilner and Oster, 1996;Carlier et al., 2003;Pollard and Borisy, 2003). In most motile cells, the network is simultaneously transported away from the leading edge in a process known as retrograde flow (Cramer, 1997). The flow may be the result of forces of membrane tension counteracting actin polymerization at the edge of the cell (Raucher and Sheetz, 2000) and/or contractile forces of myosin motors (Lin et al., 1996). The balance between forward movement of the cell and backward movement of the actin network is believed to depend on a clutch-like substrate-adhesion mechanism (Smilenov et al., 1999;Jay, 2000). When the actin network is tightly coupled to the substrate (clutch fully engaged), actin polymerization effectively pushes the plasma membrane forward, and myosin-based contraction pulls the cell body in the direction of the leading edge. Conversely, when the clutch is loose, polymerization against the membrane pushes the network backward in concert with contraction pulling the actin network away from the leading edge. Thus, a possible mechanism for the cell to control its shape and net movement is by shifting the balance between protrusion and retrograde flow, supplementing the more widespread notion of spatial variation of actin assembly being the key regulator of cell motility (Pollard et al., 2000). Indeed, several studies report a relationship between retrograde flow and cell motion: the rate of retrograde...

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Severing of F-actin by yeast cofilin is pH-independent

Pavlov

Mühlrád

Cooper

et al. 2006

Cell Motil. Cytoskeleton

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Cofilin plays an important role in actin turnover in cells by severing actin filaments and accelerating their depolymerization. The role of pH in the severing by cofilin was examined using fluorescence microscopy. To facilitate the imaging of actin filaments and to avoid the use of rhodamine phalloidin, which competes with cofilin, α-actin was labeled with tetramethylrhodamine cadaverine (TRC) at Gln 41 . The TRC-labeling inhibited actin treadmilling strongly, as measured by εATP release. Cofilin binding, detected via an increase in light scattering, and the subsequent conformational change in filament structure, as detected by TRC fluorescence decay, occurred 2-3 times faster at pH 6.8 than at pH 8.0. In contrast, actin filaments severing by cofilin was pH-independent. The pH-independent severing by cofilin was confirmed using actin labeled at Cys 374 with Oregon Green ® 488 maleimide. The depolymerization of actin by cofilin was faster at high pH.

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Cofilin (ADF) Affects Lateral Contacts in F-actin

Cited by 56 publications

References 41 publications

Cofilin Increases the Bending Flexibility of Actin Filaments: Implications for Severing and Cell Mechanics

Cofilin Increases the Bending Flexibility of Actin Filaments: Implications for Severing and Cell Mechanics

Tracking Retrograde Flow in Keratocytes: News from the Front

Severing of F-actin by yeast cofilin is pH-independent

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