title: Topological arrangement of the intracellular membrane fusion machinery.
abstract: Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) form a four-helix coiled-coil bundle that juxtaposes two bilayers and drives a basal level of membrane fusion. The Sec1/Munc18 (SM) protein binds to its cognate SNARE bundle and accelerates the basal fusion reaction. The question of how the topological arrangement of the SNARE helices affects the reactivity of the fusion proteins remains unanswered. Here we address the problem for the first time in a reconstituted system containing both SNAREs and SM proteins. We find that to be fusogenic a SNARE topology must support both basal fusion and SM stimulation. Certain topological combinations of exocytic SNAREs result in basal fusion but cannot support SM stimulation, whereas other topologies support SM stimulation without inducing basal fusion. It is striking that of all the possible topological combinations of exocytic SNARE helices, only one induces efficient fusion. Our results suggest that the intracellular membrane fusion complex is designed to fuse bilayers according to one genetically programmed topology.
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder, Boulder, CO 80309, USA.
authors.forename: Shailendra S
authors.initials: SS
authors.lastname: Rathore
authors.forename: Nilanjan
authors.initials: N
authors.lastname: Ghosh
authors.forename: Yan
authors.initials: Y
authors.lastname: Ouyang
authors.forename: Jingshi
authors.initials: J
authors.lastname: Shen
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D015870:Gene Expression; D008051:Lipid Bilayers / Q000737:chemistry*; D008081:Liposomes / Q000378:metabolism; D008561:Membrane Fusion / Q000502:physiology*; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology; D051938:Munc18 Proteins / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology; D017433:Protein Structure, Secondary; D050765:Qa-SNARE Proteins / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology; D011994:Recombinant Proteins / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015003:Yeasts / Q000737:chemistry / Q000235:genetics / Q000502:physiology*
chemical_list: D008051:Lipid Bilayers; D008081:Liposomes; D046912:Multiprotein Complexes; D051938:Munc18 Proteins; D050765:Qa-SNARE Proteins; D011994:Recombinant Proteins