title: Mobility in geometrically confined membranes.
abstract: Lipid and protein lateral mobility is essential for biological function. Our theoretical understanding of this mobility can be traced to the seminal work of Saffman and Delbrück, who predicted a logarithmic dependence of the protein diffusion coefficient (i) on the inverse of the size of the protein and (ii) on the "membrane size" for membranes of finite size [Saffman P, Delbrück M (1975) Proc Natl Acad Sci USA 72:3111-3113]. Although the experimental proof of the first prediction is a matter of debate, the second has not previously been thought to be experimentally accessible. Here, we construct just such a geometrically confined membrane by forming lipid bilayer nanotubes of controlled radii connected to giant liposomes. We followed the diffusion of individual molecules in the tubular membrane using single particle tracking of quantum dots coupled to lipids or voltage-gated potassium channels KvAP, while changing the membrane tube radius from approximately 250 to 10 nm. We found that both lipid and protein diffusion was slower in tubular membranes with smaller radii. The protein diffusion coefficient decreased as much as 5-fold compared to diffusion on the effectively flat membrane of the giant liposomes. Both lipid and protein diffusion data are consistent with the predictions of a hydrodynamic theory that extends the work of Saffman and Delbrück to cylindrical geometries. This study therefore provides strong experimental support for the ubiquitous Saffman-Delbrück theory and elucidates the role of membrane geometry and size in regulating lateral diffusion.
authors.affiliation: Institut Curie, Centre de Recherche, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 168, Physico-Chimie Curie, Université Pierre et Marie Curie, 75248 Paris, France.
authors.forename: Yegor A
authors.initials: YA
authors.lastname: Domanov
authors.forename: Sophie
authors.initials: S
authors.lastname: Aimon
authors.forename: Gilman E S
authors.initials: GE
authors.lastname: Toombes
authors.forename: Marianne
authors.initials: M
authors.lastname: Renner
authors.forename: François
authors.initials: F
authors.lastname: Quemeneur
authors.forename: Antoine
authors.initials: A
authors.lastname: Triller
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Turner
authors.forename: Patricia
authors.initials: P
authors.lastname: Bassereau
mesh_terms: D000465:Algorithms; D000818:Animals; D001692:Biological Transport; D001710:Biotin / Q000737:chemistry; D002478:Cells, Cultured; D004058:Diffusion; D017261:Glycosylphosphatidylinositols / Q000737:chemistry; D049452:Green Fluorescent Proteins / Q000737:chemistry / Q000378:metabolism; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism*; D008563:Membrane Lipids / Q000737:chemistry / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D043942:Nanotubes; D010714:Phosphatidylethanolamines / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry; D024642:Potassium Channels, Voltage-Gated / Q000737:chemistry / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D053835:Unilamellar Liposomes / Q000737:chemistry / Q000378:metabolism*
chemical_list: D017261:Glycosylphosphatidylinositols; D008051:Lipid Bilayers; D008563:Membrane Lipids; D008565:Membrane Proteins; D010714:Phosphatidylethanolamines; D024642:Potassium Channels, Voltage-Gated; D053835:Unilamellar Liposomes; D049452:Green Fluorescent Proteins; C038089:1,2-distearoylphosphatidylethanolamine; D011092:Polyethylene Glycols; D001710:Biotin