title: Steric hindrance of SNARE transmembrane domain organization impairs the hemifusion-to-fusion transition.
abstract: SNAREs fuse membranes in several steps. Trans-SNARE complexes juxtapose membranes, induce hemifused stalk structures, and open the fusion pore. A recent penetration model of fusion proposed that SNAREs force the hydrophilic C-termini of their transmembrane domains through the hydrophobic core of the membrane(s). In contrast, the indentation model suggests that the C-termini open the pore by locally compressing and deforming the stalk. Here we test these models in the context of yeast vacuole fusion. Addition of small hydrophilic tags renders bilayer penetration by the C-termini energetically unlikely. It preserves fusion activity, however, arguing against the penetration model. Addition of large protein tags to the C-termini permits SNARE activation, trans-SNARE pairing, and hemifusion but abolishes pore opening. Fusion proceeds if the tags are detached from the membrane by a hydrophilic spacer or if only one side of the trans-SNARE complex carries a protein tag. Thus, both sides of a trans-SNARE complex can drive pore opening. Our results are consistent with an indentation model in which multiple SNARE C-termini cooperate in opening the fusion pore by locally deforming the inner leaflets.
authors.affiliation: Département de Biochimie, Université de Lausanne, Epalinges, Switzerland.
authors.forename: Massimo
authors.initials: M
authors.lastname: D'Agostino
authors.affiliation: Department of Theoretical Physics, Georg-August University, Goettingen, Germany.|Leibniz-Institut für Oberflächenmodifizierung, Leipzig, Germany.
authors.forename: Herre Jelger
authors.initials: HJ
authors.lastname: Risselada
authors.affiliation: Département de Biochimie, Université de Lausanne, Epalinges, Switzerland andreas.mayer@unil.ch.
authors.forename: Andreas
authors.identifier: 0000-0001-6131-313X
authors.initials: A
authors.lastname: Mayer
mesh_terms: D002462:Cell Membrane; D005089:Exocytosis; D008051:Lipid Bilayers; D008247:Lysosomes / Q000502:physiology; D008561:Membrane Fusion / Q000502:physiology*; D011485:Protein Binding; D050600:SNARE Proteins / Q000737:chemistry* / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism; D014617:Vacuoles / Q000502:physiology*; D033921:Vesicular Transport Proteins
chemical_list: D008051:Lipid Bilayers; D050600:SNARE Proteins; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins
keywords: SNAREs; exocytosis; lysosome; membrane fusion; vacuole