Composition of isolated synaptic boutons reveals the amounts of vesicle trafficking proteins

TLDR

Synaptic vesicle recycling has long been used as a model for cellular trafficking mechanisms. The authors integrated quantitative immunoblotting, mass spectrometry, electron microscopy, and super‑resolution fluorescence microscopy to count proteins, measure organelle dimensions, and localize proteins, then built a 3‑D model of an average synapse containing ~300,000 proteins at atomic detail. Protein copy numbers within each recycling step correlated tightly, yet differed by over three orders of magnitude across steps, ranging from ~150 copies for endosomal fusion proteins to >20,000 for exocytotic proteins.

Abstract

Synaptic vesicle recycling has long served as a model for the general mechanisms of cellular trafficking. We used an integrative approach, combining quantitative immunoblotting and mass spectrometry to determine protein numbers; electron microscopy to measure organelle numbers, sizes, and positions; and super-resolution fluorescence microscopy to localize the proteins. Using these data, we generated a three-dimensional model of an "average" synapse, displaying 300,000 proteins in atomic detail. The copy numbers of proteins involved in the same step of synaptic vesicle recycling correlated closely. In contrast, copy numbers varied over more than three orders of magnitude between steps, from about 150 copies for the endosomal fusion proteins to more than 20,000 for the exocytotic ones.