Polymer-induced bundling of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>F</mml:mi></mml:mrow></mml:math>actin and the depletion force

Hošek, Martin; Tang, Jay X.

doi:10.1103/physreve.69.051907

Cited by 94 publications

(102 citation statements)

References 35 publications

(63 reference statements)

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“…The formation of filament bundles in F-but not G-buffer gives credence to the idea that an ionic strength-dependent conformation change in either the formin or the actin is required for formin interaction with the side of the actin filament. A large body of data does suggest that ionic strength is a major determinant of actin conformation in agreement with this hypothesis (41,42).…”

Section: Discussionsupporting

confidence: 61%

Differential Regulation of Actin Polymerization and Structure by Yeast Formin Isoforms

Wen

Rubenstein

2009

Journal of Biological Chemistry

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The budding yeast formins, Bnr1 and Bni1, behave very differently with respect to their interactions with muscle actin. However, the mechanisms underlying these differences are unclear, and these formins do not interact with muscle actin in vivo. We use yeast wild type and mutant actins to further assess these differences between Bnr1 and Bni1. Low ionic strength G-buffer does not promote actin polymerization. However, Bnr1, but not Bni1, causes the polymerization of pyrene-labeled Mg-G-actin in G-buffer into single filaments based on fluorometric and EM observations. Polymerization by Bnr1 does not occur with Ca-G-actin. By cosedimentation, maximum filament formation occurs at a Bnr1:actin ratio of 1:2. The interaction of Bnr1 with pyrene-labeled S265C Mg-actin yields a pyrene excimer peak, from the cross-strand interaction of pyrene probes, which only occurs in the context of F-actin. In F-buffer, Bnr1 promotes much faster yeast actin polymerization than Bni1. It also bundles the F-actin in contrast to the low ionic strength situation where only single filaments form. Thus, the differences previously observed with muscle actin are not actin isoformspecific. The binding of both formins to F-actin saturate at an equimolar ratio, but only about 30% of each formin cosediments with F-actin. Finally, addition of Bnr1 but not Bni1 to pyrenelabeled wild type and S265C Mg-F actins enhanced the pyreneand pyrene-excimer fluorescence, respectively, suggesting Bnr1 also alters F-actin structure. These differences may facilitate the ability of Bnr1 to form the actin cables needed for polarized delivery of nutrients and organelles to the growing yeast bud.Bni1 and Bnr1 are the two formin isoforms expressed in Saccharomyces cerevisiae (1, 2). These proteins, as other isoforms in the formin family, are large multidomain proteins (3, 4). Several regulatory domains, including one for binding the G-protein rho, are located at the N-terminal half of the protein (4 -7). FH1, FH2, and Bud6 binding domains are located in the C-terminal half of the protein (8). The formin homology 1 (FH1) 2 domain contains several sequential poly-L-proline motifs, and it interacts with the profilin/actin complex to recruit actin monomers and regulate the insertion of actin monomers at the barbed end of actin (9 -11). The fomin homology domain 2 (FH2) forms a donut-shaped homodimer, which wraps around actin dimers at the barbed end of actin filaments (12, 13). One important function of formin is to facilitate actin polymerization by stabilizing actin dimers or trimers under polymerization conditions and then to processively associate with the barbed end of the elongating filament to control actin filament elongation kinetics (13-18).A major unsolved protein in the study of formins is the elucidation of the individual functions of different isoforms and their regulation. In vivo, these two budding yeast formins have distinct cellular locations and dynamics (1,2,19,20). Bni1 concentrates at the budding site before the daughter cell buds from the mother c...

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Section: Discussionsupporting

confidence: 61%

Differential Regulation of Actin Polymerization and Structure by Yeast Formin Isoforms

Wen

Rubenstein

2009

Journal of Biological Chemistry

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“…Therefore, despite the entropy of the large particle decreasing due to its confinement, the increasing entropy of the small particles increases the total entropy and eventually reduces the free energy of the whole system. This physical process also has significant biological implications [11,12]. For example, if the larger particle is replaced by macromolecules and the smaller ones by polymer coils or small globular proteins, one can see that the presence of the smaller objects will likely drive the macromolecules to aggregate to the vesicle wall.…”

Section: Introductionmentioning

confidence: 99%

Depletion effect and biomembrane budding

et al. 2013

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Depletion effects are well known to lead to phase separation in microsystems consisting of large and small particles with short-range repulsive interactions that act over macromolecular length scales. The equilibrium mechanics between an enveloped colloidal particle and a biomembrane caused by entropy is investigated by using a continuum model. We show that the favorable contact energy stems from entropy, which is sufficient to drive engulfment of the colloidal particle, and deformation of the biomembrane determines the resistance to the engulfment of the colloidal particle. The engulfment process depends on the ratio of the radii of the larger particle and smaller particles and the bending rigidity. The results show insights into the effects of depletion on biomembrane budding and nanoparticle transportation by a vesicle.

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“…Depletion forces induced by small molecules present in the cytosol may also act as effective crosslinkers that bundle F-actin, as demonstrated in vitro using polyethylene glycol (PEG) 27,28 . To examine the potential role of depletion forces on F-actin bundle stiffness, we also measured B κ in the presence of PEG (MW 6 kDa, 2 & 4% w/w).…”

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confidence: 99%