title: Roles of amphipathic helices and the bin/amphiphysin/rvs (BAR) domain of endophilin in membrane curvature generation.
abstract: Control of membrane curvature is required in many important cellular processes, including endocytosis and vesicular trafficking. Endophilin is a bin/amphiphysin/rvs (BAR) domain protein that induces vesicle formation by promotion of membrane curvature through membrane binding as a dimer. Using site-directed spin labeling and EPR spectroscopy, we show that the overall BAR domain structure of the rat endophilin A1 dimer determined crystallographically is maintained under predominantly vesiculating conditions. Spin-labeled side chains on the concave surface of the BAR domain do not penetrate into the acyl chain interior, indicating that the BAR domain interacts only peripherally with the surface of a curved bilayer. Using a combination of EPR data and computational refinement, we determined the structure of residues 63-86, a region that is disordered in the crystal structure of rat endophilin A1. Upon membrane binding, residues 63-75 in each subunit of the endophilin dimer form a slightly tilted, amphipathic alpha-helix that directly interacts with the membrane. In their predominant conformation, these helices are located orthogonal to the long axis of the BAR domain. In this conformation, the amphipathic helices are positioned to act as molecular wedges that induce membrane curvature along the concave surface of the BAR domain.
authors.affiliation: Zilkha Neurogenetic Institute, University of Southern California, Los Angeles, California 90033, USA.
authors.forename: Christine C
authors.initials: CC
authors.lastname: Jao
authors.forename: Balachandra G
authors.initials: BG
authors.lastname: Hegde
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Gallop
authors.forename: Prabhavati B
authors.initials: PB
authors.lastname: Hegde
authors.forename: Harvey T
authors.initials: HT
authors.lastname: McMahon
authors.forename: Ian S
authors.initials: IS
authors.lastname: Haworth
authors.forename: Ralf
authors.initials: R
authors.lastname: Langen
mesh_terms: D000217:Acyltransferases / Q000737:chemistry* / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D008560:Membrane Fluidity; D008854:Microscopy, Electron; D008954:Models, Biological; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D051381:Rats; D013113:Spin Labels
chemical_list: D008081:Liposomes; D013113:Spin Labels; D000217:Acyltransferases; C018764:2-acylglycerophosphate acyltransferase