The full-length cell–cell fusogen EFF-1 is monomeric and upright on the membrane

• Published in: Nature communications Vol. 5; no. 1; p. 3912
• Main Authors: Zeev-Ben-Mordehai, Tzviya, Vasishtan, Daven, Siebert, C. Alistair, Grünewald, Kay
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 28.05.2014; Nature Publishing Group; Nature Pub. Group
• Subjects: 101/28; 631/45/535; 631/57/2272/2273; 631/80/313; Animals; Caenorhabditis elegans - cytology; Caenorhabditis elegans - metabolism; Caenorhabditis elegans Proteins - metabolism; Cell Fusion; Cell Line; Cell Membrane - metabolism; Cricetinae; Humanities and Social Sciences; Mass Spectrometry; Membrane Glycoproteins - metabolism; Models, Biological; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms4912

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. Cell–cell fusion in Caenorhabditis elegans is mediated by EFF-1 and AFF-1 proteins. Here, the authors present an electron cryomicroscopy 3D reconstruction of EFF-1 in the membrane, and combine snapshots of membrane fusion in vitro with a recently reported crystal structure to propose a mechanism for the fusion process.