Local entropic effects of polymers grafted to soft interfaces

Bickel, Thomas; Jeppesen, Claus; Marques, Carlos M.

doi:10.1007/s101890170140

Cited by 63 publications

(94 citation statements)

References 34 publications

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“…When the CTT is in the VDAC pore, it can be divided into two domains: the trans-membrane domain, which has already passed through the pore, has length /2, and can be treated as a polymer tethered to an impenetrable infinite wall (the membrane); and the cis domain, which has length /2 and can be considered to be tethered to both the membrane and the tubulin body. In both cases, for simplicity, we describe the space of possible polymer conformations as a non-self-avoiding random walk of a polymer tethered to an impenetrable infinite wall, for which the Green's function (in cylindrical coordinates , , ) is calculated from the method of images (66,67):…”

Section: Appendixmentioning

confidence: 99%

Sequence diversity of tubulin isotypes in regulation of the mitochondrial voltage-dependent anion channel

Rostovtseva

Gurnev

Hoogerheide

et al. 2018

Journal of Biological Chemistry

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The microtubule protein tubulin is a heterodimer comprising / subunits, in which each subunit features multiple isotypes in vertebrates. For example, seven -tubulin and eight -tubulin isotypes in the human tubulin gene family vary mostly in the length and primary sequence of the disordered anionic C-terminal tails (CTTs). The biological reason for such sequence diversity remains a topic of vigorous enquiry. Here, we demonstrate that it may be a key feature of tubulin's role in regulation of the permeability of the mitochondrial outer membrane voltagedependent anion channel (VDAC). Using recombinant yeast /-tubulin constructs with -CTTs, -CTTs, or both from various human tubulin isotypes, we probed their interactions with VDAC reconstituted into planar lipid bilayers. A comparative study of the blockage kinetics revealed that either -CTTs or -CTTs block VDAC pore and that the efficiency of blockage by individual CTTs spans two orders of magnitude, depending on the CTT isotype.-Tubulin constructs, notably 3, blocked VDAC most effectively. We quantitatively describe these experimental results using a physical model that accounts only for the number and distribution of charges in the CTT, and not for the interactions between specific residues on the CTT and VDAC pore. Based on these results, we speculate that the effectiveness of VDAC regulation by tubulin depends on the predominant tubulin isotype in a cell. Consequently, the fluxes of ATP/ADP http://www.jbc.org/cgi

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Section: Appendixmentioning

confidence: 99%

Sequence diversity of tubulin isotypes in regulation of the mitochondrial voltage-dependent anion channel

Rostovtseva

Gurnev

Hoogerheide

et al. 2018

Journal of Biological Chemistry

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“…It has been shown recently that the first-order term of the expansion is related to the pressure field applied by the grafted chain to the surface [16,17]. At distance r = x 2 + y 2 from the grafting point, this entropic pressure decays with the scaling form p(r) ∼ k B T r −3 (a ≪ r ≪ R g ) in both good and theta solvents, and then vanishes sharply beyond R g [18].…”

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confidence: 99%

Scale-dependent rigidity of polymer-ornamented membranes

Bickel

Marques

2002

Eur. Phys. J. E

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We study the fluctuation spectrum of fluid membranes carrying grafted polymers. Contrary to usual descriptions, we find that the modifications induced by the polymers cannot be reduced to the renormalization of the membrane bending rigidity. Instead we show that the ornamented membrane exhibits a scale-dependent elastic modulus that we evaluate. In ornamented lamellar stacks, we further show that this leads to a modification of the Caillé parameter characterizing the power-law singularities of the Bragg peaks. PACS numbers: 36.20, 87.16.Dg, 82.35.Gh The characterization of polymer-membrane interactions is a fundamental issue of colloidal science. In cosmetics, pharmaceutics or detergency, many formulations are suspensions of self-assembled surfactant bilayers with polymers added for performance, processing, conditioning or delivery [1]. Likewise, lipid bilayers form the walls of living cells and liposomes, and host a great variety of macromolecules for coating protection, ion exchange and mechanical reinforcement. [2]. In many instances, the polymers are end-tethered to the soft interfaces. Grafting is easily achieved experimentally by using polymer chains that carry hydrophobic groups. Typical examples are provided by the so-called PEG-lipids, hydrophilic chains of polyethylene glycol covalently linked to a double-tail phospholipid molecule. Recent studies have shown that polymers grafted to bilayers can induce gelation [3] or other phase changes [4,5] in liquid lamellar phases. They stabilize monodisperse vesicles [6] and modify the geometry of monolamellar [7,8] and multilamellar [9] cylindrical vesicles. They also lead to drastic changes in the structure and phase behaviour of ternary amphiphilic systems [10].As first explained by Canham and Helfrich, fluid membranes are fluctuating objects [11]. In thermal equilibrium, the surface assumes all the possible shapes allowed by the geometry with the associated Boltzmann probability P ∼ exp{−H 0 /(k B T )}. The Hamiltonian H 0 is a quadratic function of c 1 and c 2 , the two principal curvatures at any given point of the surface,The spontaneous curvature c 0 vanishes for symetric bilayers. The Gaussian rigidityκ plays an important role in the determination of the topology of the system, and the integral dSκc 1 c 2 does not depend on the particular shape of the membrane. The amplitude of the thermal fluctuations is controled by the bending rigidity κ, that ranges from a few k B T to a few tens of k B T . Conversely, the analysis of the height correlations in a membrane system allows for the determination of the constitutive rigidity. Many techniques were specifically developped to extract κ by comparing experiments and theoretical predictions for vesicles, lamellar stacks, bicontinuous phases and other geometries. These methods have so far been of limited application in polymer-membrane systems because of the lack of prediction for the fluctuation spectrum of bilayers in the presence of polymers. In this Letter, we make a first step to reach this gap by investi...

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“…[15][16][17][18][19]. One reason for this approach is that the simplified models available from polymer physics allow for a more or less exact computation of the entropic pressure exerted by the polymer on the membrane.…”

Section: Introductionmentioning

confidence: 99%

Interactions between proteins bound to biomembranes

2003

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We study a physical model for the interaction between general inclusions bound to fluid membranes that possess finite tension γ, as well as the usual bending rigidity κ. We are motivated by an interest in proteins bound to cell membranes that apply forces to these membranes, due to either entropic or direct chemical interactions. We find an exact analytic solution for the repulsive interaction between two similar circularly symmetric inclusions. This repulsion extends over length scales ∼ κ/γ and contrasts with the membrane-mediated contact attraction for similar inclusions on tensionless membranes. For non circularly symmetric inclusions we study the small, algebraically long-ranged, attractive contribution to the force that arises. We discuss the relevance of our results to biological phenomena, such as the budding of caveolae from cell membranes and the striations that are observed on their coats. These, and other, "gnarly buds" may prove fascinating to study further.

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Local entropic effects of polymers grafted to soft interfaces

Cited by 63 publications

References 34 publications

Sequence diversity of tubulin isotypes in regulation of the mitochondrial voltage-dependent anion channel

Sequence diversity of tubulin isotypes in regulation of the mitochondrial voltage-dependent anion channel

Scale-dependent rigidity of polymer-ornamented membranes

Interactions between proteins bound to biomembranes

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