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 ~134 nm in diameter, and only 20% of them (all ≥ 80 nm) 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.

Mechanistic Determinants of Slow Axonal Transport and Presynaptic Targeting of Clathrin Packets

“…Such intact clathrin-structures are surprising, given the transient nature of clathrin, and we reason that these represent transport-packets. The diameter of these clathrin-structures as determined by EM was ~ 50nm and ~125nm (spherical core and outer diameter respectively); consistent with previous cryo-EM studies of in vitro reconstituted clathrin (Heymann et al, 2013).…”

Three-dimensional Structure of the Toxin-delivery Particle Antifeeding Prophage of Serratia entomophila

“…The correct hand of the Afp particles was established by processing in parallel a specimen of vitrified coated vesicles, for which the handedness is known (25) using the same microscope conditions and the same software (26).…”

Molecular Structure, Function, and Dynamics of Clathrin-Mediated Membrane Traffic

“…Coated vesicles isolated from cells or tissues are substantially more heterogeneous in size and shape than the coats assembled for cryoEM studies (Cheng et al 2007;Heymann et al 2013). Tomographic reconstructions of individual coated vesicles illustrate the variety of lattices present in a preparation from bovine brain ( Fig.…”