Tandem MS analysis of brain clathrin-coated vesicles reveals their critical involvement in synaptic vesicle recycling

Tandem MS has identified 209 proteins of clathrin-coated vesicles (CCVs) isolated from rat brain. An overwhelming abundance of peptides were assigned to the clathrin coat with a 1:1 stoichiometry observed for clathrin heavy and light chains and a 2:1 stoichiometry of clathrin heavy chain with clathrin adaptor protein heterotetramers. Thirty-two proteins representing many of the known components of synaptic vesicles (SVs) were identified, supporting that a main function for brain CCVs is to recapture SVs after exocytosis. A ratio of vesicle-N-ethylmaleimide-sensitive factor attachment protein receptors to target-N-ethylmaleimide-sensitive factor attachment protein receptors, similar to that previously detected on SVs, supports a single-step model for SV sorting during CCV-mediated recycling of SVs. The uncovering of eight previously undescribed proteins, four of which have to date been linked to clathrin-mediated trafficking, further attests to the value of the current organelle-based proteomics strategy.