Generation of Coated Intermediates of Clathrin-Mediated Endocytosis on Protein-Free Liposomes

TLDR

In synaptic membranes, dynamin‑ and clathrin‑coated intermediates are typically coupled, but on liposomes they can form independently and even without nucleotides, suggesting that membrane proteins mainly regulate coat assembly temporally and spatially. Clathrin‑coated buds and dynamin‑coated tubules morphologically similar to those in synaptic membranes can be generated on protein‑free liposomes by incubating with cytosol or with clathrin coat proteins and purified dynamin, respectively. These results show that lipid–cytosolic protein interfaces alone are sufficient to deform lipid bilayers into buds and tubules.

Abstract

Clathrin-coated buds and dynamin-coated tubules morphologically similar to corresponding structures observed in synaptic membranes can be generated on protein-free liposomes by incubation with cytosol, or with clathrin coat proteins and purified dynamin, respectively. Dynamin- and clathrin-coated intermediates may form independently of each other, despite the coupling between the two processes typically observed in synaptic membranes. Formation of both structures on liposomes can occur in the absence of nucleotides. These findings indicate that interfaces between lipids and cytosolic proteins are fully sufficient to deform lipids bilayers into buds and tubules. They suggest that a main function of membrane proteins is to act as positive and negative regulators of coat assembly, therefore controlling these processes in time and space.