title: The full-length cell-cell fusogen EFF-1 is monomeric and upright on the membrane.
abstract: Fusogens are membrane proteins that remodel lipid bilayers to facilitate membrane merging. Although several fusogen ectodomain structures have been solved, structural information on full-length, natively membrane-anchored fusogens is scarce. Here we present the electron cryo microscopy three-dimensional reconstruction of the Caenorhabditis elegans epithelial fusion failure 1 (EFF-1) protein natively anchored in cell-derived membrane vesicles. This reveals a membrane protruding, asymmetric, elongated monomer. Flexible fitting of a protomer of the EFF-1 crystal structure, which is homologous to viral class-II fusion proteins, shows that EFF-1 has a hairpin monomeric conformation before fusion. These structural insights, when combined with our observations of membrane-merging intermediates between vesicles, enable us to propose a model for EFF-1 mediated fusion. This process, involving identical proteins on both membranes to be fused, follows a mechanism that shares features of SNARE-mediated fusion while using the structural building blocks of the unilaterally acting class-II viral fusion proteins.
authors.affiliation: Oxford Particle Imaging Centre, Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK.
authors.forename: Tzviya
authors.initials: T
authors.lastname: Zeev-Ben-Mordehai
authors.affiliation: Oxford Particle Imaging Centre, Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK.
authors.forename: Daven
authors.initials: D
authors.lastname: Vasishtan
authors.affiliation: Oxford Particle Imaging Centre, Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK.
authors.forename: C Alistair
authors.initials: CA
authors.lastname: Siebert
authors.affiliation: Oxford Particle Imaging Centre, Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK.
authors.forename: Kay
authors.initials: K
authors.lastname: Grünewald
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000166:cytology* / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism*; D002459:Cell Fusion; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D006224:Cricetinae; D013058:Mass Spectrometry; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008954:Models, Biological
chemical_list: C520081:AFF-1 protein, C elegans; D029742:Caenorhabditis elegans Proteins; C470734:EFF-1 protein, C elegans; D008562:Membrane Glycoproteins