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Review
. 2014 Aug:29:53-60.
doi: 10.1016/j.ceb.2014.03.006. Epub 2014 Apr 18.

Mechanisms shaping cell membranes

Michael M Kozlov  1 , Felix Campelo  2 , Nicole Liska  3 , Leonid V Chernomordik  4 , Siewert J Marrink  5 , Harvey T McMahon  6
Affiliations
Review

Mechanisms shaping cell membranes

Michael M Kozlov et al. Curr Opin Cell Biol. 2014 Aug.

Abstract

Membranes of intracellular organelles are characterized by large curvatures with radii of the order of 10-30nm. While, generally, membrane curvature can be a consequence of any asymmetry between the membrane monolayers, generation of large curvatures requires the action of mechanisms based on specialized proteins. Here we discuss the three most relevant classes of such mechanisms with emphasis on the physical requirements for proteins to be effective in generation of membrane curvature. We provide new quantitative estimates of membrane bending by shallow hydrophobic insertions and compare the efficiency of the insertion mechanism with those of the protein scaffolding and crowding mechanisms.

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Figures

Fig. 1
Fig. 1. Lipid binding and vesiculation by epsin ENTH domain
A. Epsin ENTH is a soluble domain and so is found in the supernatant (Sup) after centrifugation at 53664×g. In contrast, 200nm liposomes (Avanti Folch with 0.5% PI(4,5)P2 added) largely pellet (Pel) on centrifugation. When both are present, epsin ENTH binds to the liposomes, and while some protein pellets with the liposomes, some of the liposomes move to the supernatant. This reversal of liposome pelleting is the result of generation by insertion of epsin amphipathic helices of smaller liposomes characterized by large curvatures, which bud off from the initial liposomes and cannot be pelleted (as in [46]). Thus this is a biochemical assay to show at a bulk level the consequences of epsin ENTH helix insertion on curvature generation and membrane fission. This differential centrifugation assay, which can biochemically distinguish between liposomes greater than 100nm diameter and small vesicles of 50nm diameter or less, has previously been published in [46]. B. A question arises as to whether curvature generation could equally be promoted by a crowding mechanism. So using the same assay conditions as in A, His6-tagged GFP or His6-tagged epsin ENTH domains with deleted amphipathic helices were attached to liposomes (using the protocol of [44]) via incorporated DOGS-NTA (Ni) lipids (presence of an additional 4% NTA lipids, and even more protein binds/pellets with 10% NTA lipids). Neither GFP nor epsin ENTH domain without its amphipathic helix result in vesiculation of liposomes, and thus if they are capable of curvature generation it is not on the same scale as the ENTH domain with an intact amphipathic helix.
Fig. 2
Fig. 2
Effective spontaneous curvature of a rod-like hydrophobic insertion is represented as a function of the rod radius, r, for monolayer thicknesses of h = 1.5 nm(black) and h = 2 nm (blue).
Fig. 3
Fig. 3. Putative membrane binding footprint of epsin ENTH domain
A. Membrane interaction surface of epsin1 ENTH domain viewed from the membrane. The amphipathic helix, which inserts into the membrane is shown in dark green with amino acid side chains included. B. Space filled representation of (A) with side chains included for the whole protein, overlaid with a carbon atom lattice (to facilitate area calculations), showing that the amphipathic helix occupies approximately 1/3rd of the total projection area.
Fig. 4
Fig. 4
Membrane curvature generated by epsin ENTH domains as predicted by different models. The membrane tube radius was calculated for the hydrophobic insertion model (blue line), the protein-protein crowding model (red line), and a combined model (pink line), and is represented as a function of the membrane area coverage by ENTH. The dashed black line represents the observed radius of tubes generated by epsin ENTH domains [51]. The relative area fraction of the amphipathic helices to the total surface area of the ENTH is taken to be: (A) AAH/AENTH = 0.3, (B) AAH/AENTH = 0.1. The monolayer thickness h = 2 nm and the insertion is modelled as a rigid cylinder of a radius r = 0.5nm which embeds to the depth d = 0.8 nm into the membrane. The crowding model line has been taken as in Fig. 3C of Ref. [44] with replacement of the spontaneous curvature, Js, by the radius, R = 1/Js. Specifically, the curve has been calculated using Eqs. (4–5) of the Supplementary note of Ref. [44] using the same parameter values as in Ref. [44].
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References

    1. Voeltz GK, Rolls MM, Rapoport TA. Structural organization of the endoplasmic reticulum. EMBO Rep. 2002;3:944–950. - PMC - PubMed
    1. Shibata Y, Voeltz GK, Rapoport TA. Rough sheets and smooth tubules. Cell. 2006;126:435–439. - PubMed
    1. Terasaki M, Shemesh T, Kasthuri N, Klemm RW, Schalek R, Hayworth KJ, Hand AR, Yankova M, Huber G, Lichtman JW, et al. Stacked endoplasmic reticulum sheets are connected by helicoidal membrane motifs. Cell. 2013;154:285–296. - PMC - PubMed
    1. Puhka M, Joensuu M, Vihinen H, Belevich I, Jokitalo E. Progressive sheet-to-tubule transformation is a general mechanism for endoplasmic reticulum partitioning in dividing mammalian cells. Mol Biol Cell. 2012;23:2424–2432. - PMC - PubMed
    1. Ladinsky MS, Mastronarde DN, McIntosh JR, Howell KE, Staehelin LA. Golgi structure in three dimensions: functional insights from the normal rat kidney cell. J Cell Biol. 1999;144:1135–1149. - PMC - PubMed

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