title: Clathrin-coated vesicles from brain have small payloads: a cryo-electron tomographic study.
abstract: Clathrin coats, which stabilize membrane curvature during endocytosis and vesicular trafficking, form highly polymorphic fullerene lattices. We used cryo-electron tomography to visualize coated particles in isolates from bovine brain. The particles range from ∼66 to ∼134nm in diameter, and only 20% of them (all ⩾80nm) contain vesicles. The remaining 80% are clathrin "baskets", presumably artifactual assembly products. Polyhedral models were built for 54 distinct coat geometries. In true coated vesicles (CVs), most vesicles are offset to one side, leaving a crescent of interstitial space between the coat and the membrane for adaptor proteins and other components. The latter densities are fewer on the membrane-proximal side, which may represent the last part of the vesicle to bud off. A small number of densities - presumably cargo proteins - are associated with the interior surface of the vesicles. The clathrin coat, adaptor proteins, and vesicle membrane contribute almost all of the mass of a CV, with most cargoes accounting for only a few percent. The assembly of a CV therefore represents a massive biosynthetic effort to internalize a relatively diminutive payload. Such a high investment may be needed to overcome the resistance of membranes to high curvature.
authors.affiliation: Laboratory of Structural Biology Research, National Institute of Arthritis, Musculoskeletal and Skin Diseases, Bethesda, MD 20892, United States. Electronic address: Bernard_Heymann@nih.gov.
authors.forename: J Bernard
authors.initials: JB
authors.lastname: Heymann
authors.forename: Dennis C
authors.initials: DC
authors.lastname: Winkler
authors.forename: Yang-In
authors.initials: YI
authors.lastname: Yim
authors.forename: Evan
authors.initials: E
authors.lastname: Eisenberg
authors.forename: Lois E
authors.initials: LE
authors.lastname: Greene
authors.forename: Alasdair C
authors.initials: AC
authors.lastname: Steven
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D002417:Cattle; D022163:Clathrin-Coated Vesicles / Q000378:metabolism*; D055032:Electron Microscope Tomography / Q000379:methods; D004583:Electrons
keywords: AP; Adaptor proteins; CB; CV; Clathrin-mediated endocytosis; Cryo-electron microscopy; Fullerenes; Three-dimensional image reconstruction; adaptor protein; clathrin basket; coated vesicle