title: Membrane curvature sensing by amphipathic helices: a single liposome study using α-synuclein and annexin B12.
abstract: Preferential binding of proteins on curved membranes (membrane curvature sensing) is increasingly emerging as a general mechanism whereby cells may effect protein localization and trafficking. Here we use a novel single liposome fluorescence microscopy assay to examine a common sensing motif, the amphipathic helix (AH), and provide quantitative measures describing and distinguishing membrane binding and sensing behavior. By studying two AH-containing proteins, α-synuclein and annexin B12, as well as a range of AH peptide mutants, we reveal that both the hydrophobic and hydrophilic faces of the helix greatly influence binding and sensing. Although increased hydrophobic and electrostatic interactions with the membrane both lead to greater densities of bound protein, the former yields membrane curvature-sensitive binding, whereas the latter is not curvature-dependent. However, the relative contributions of both components determine the sensing of AHs. In contrast, charge density in the lipid membrane seems important primarily in attracting AHs to the membrane but does not significantly influence sensing. These observations were made possible by the ability of our assay to distinguish within our samples liposomes with and without bound protein as well as the density of bound protein. Our findings suggest that the description of membrane curvature-sensing requires consideration of several factors such as short and long range electrostatic interactions, hydrogen bonding, and the volume and structure of inserted hydrophobic residues.
authors.affiliation: Bionanotechnology and Nanomedicine Laboratory, Department of Neuroscience and Pharmacology, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark; Nano-Science Center, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark.
authors.forename: Martin Borch
authors.initials: MB
authors.lastname: Jensen
authors.affiliation: Bionanotechnology and Nanomedicine Laboratory, Department of Neuroscience and Pharmacology, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark; Nano-Science Center, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark; Lundbeck Foundation Center Biomembranes in Nanomedicine, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark.
authors.forename: Vikram Kjøller
authors.initials: VK
authors.lastname: Bhatia
authors.affiliation: Zilkha Neurogenetic Institute, University of Southern California, Los Angeles, California 90033.
authors.forename: Christine C
authors.initials: CC
authors.lastname: Jao
authors.affiliation: IGM-Bioorganic Chemistry, Faculty of Life Sciences, University of Copenhagen, 1871 Frederiksberg C, Denmark.
authors.forename: Jakob Ewald
authors.initials: JE
authors.lastname: Rasmussen
authors.affiliation: IGM-Bioorganic Chemistry, Faculty of Life Sciences, University of Copenhagen, 1871 Frederiksberg C, Denmark.
authors.forename: Søren L
authors.initials: SL
authors.lastname: Pedersen
authors.affiliation: IGM-Bioorganic Chemistry, Faculty of Life Sciences, University of Copenhagen, 1871 Frederiksberg C, Denmark.
authors.forename: Knud J
authors.initials: KJ
authors.lastname: Jensen
authors.affiliation: Zilkha Neurogenetic Institute, University of Southern California, Los Angeles, California 90033.
authors.forename: Ralf
authors.initials: R
authors.lastname: Langen
authors.affiliation: Bionanotechnology and Nanomedicine Laboratory, Department of Neuroscience and Pharmacology, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark; Nano-Science Center, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark; Lundbeck Foundation Center Biomembranes in Nanomedicine, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark. Electronic address: stamou@nano.ku.dk.
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Stamou
mesh_terms: D000818:Animals; D017302:Annexins / Q000737:chemistry*; D001921:Brain / Q000378:metabolism; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism*; D002627:Chemistry, Physical / Q000379:methods; D006801:Humans; D006860:Hydrogen Bonding; D008051:Lipid Bilayers / Q000737:chemistry; D008055:Lipids / Q000737:chemistry; D008081:Liposomes / Q000737:chemistry; D008563:Membrane Lipids / Q000737:chemistry; D010455:Peptides / Q000737:chemistry; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry; D012542:Scattering, Radiation; D055672:Static Electricity; D051844:alpha-Synuclein / Q000378:metabolism*
chemical_list: D017302:Annexins; D008051:Lipid Bilayers; D008055:Lipids; D008081:Liposomes; D008563:Membrane Lipids; D010455:Peptides; D011506:Proteins; D051844:alpha-Synuclein