title: Change of line tension in phase-separated vesicles upon protein binding.
abstract: We measured the effect of a model membrane-binding protein on line tension and morphology of phase-separated lipid-bilayer vesicles. We studied giant unilamellar vesicles composed of a cholesterol/dioleoylphosphatidylcholine/palmitoylsphingomyelin mixture and a controlled mole fraction of a Ni-chelating lipid. These vesicles exhibited two coexisting fluid-phase domains at room temperature. Owing to the line tension, σ, between the two phases, the boundary between them was pulled like a purse string so that the smaller domain formed a bud. While observing the vesicles in a microscope, histidine-tagged green fluorescent protein was added, which bound to the Ni-chelating lipid. As protein bound, the vesicle shape changed and the length of the phase boundary increased. The change in morphology was attributed to a reduction of σ between the two phases because of preferential accumulation of histidine-tagged green fluorescent protein-Ni-chelating lipid clusters at the domain boundary. Greater reductions of σ were found in samples with higher concentrations of Ni-chelating lipid; this trend provided an estimate of the binding energy at the boundary, approximately k(B)T. The results show how domain boundaries can lead to an accumulation of membrane-binding proteins at their boundaries and, in turn, how proteins can alter line tension and vesicle morphology.
authors.affiliation: Department of Physics, University of Massachusetts, Amherst, Massachusetts, United States.
authors.forename: Jaime B
authors.initials: JB
authors.lastname: Hutchison
authors.forename: Robert M
authors.initials: RM
authors.lastname: Weis
authors.forename: Anthony D
authors.initials: AD
authors.lastname: Dinsmore
mesh_terms: D049452:Green Fluorescent Proteins / Q000378:metabolism; D008051:Lipid Bilayers; D008856:Microscopy, Fluorescence; D011485:Protein Binding; D011506:Proteins / Q000378:metabolism*; D013696:Temperature
chemical_list: D008051:Lipid Bilayers; D011506:Proteins; D049452:Green Fluorescent Proteins