Molecular mechanisms in clathrin-mediated membrane budding revealed through subcellular proteomics

Subcellular proteomics is a powerful new approach that combines subcellular fractionation and MS (mass spectrometry) to identify the protein complement of cellular compartments. The approach has been applied to isolated organelles and major suborganellar structures and each study has identified known proteins not previously understood to associate with the compartment and novel proteins that had been described only as predicted open-reading frames from genome sequencing data. We have utilized subcellular proteomics to analyse the protein components of CCVs (clathrin-coated vesicles) isolated from adult brain. Accounting for identified fragmented peptides allows for a quantitative assessment of protein complexes associated with CCVs, and the identification of many of the known components of post-fusion synaptic vesicles demonstrates that a main function for brain CCVs is to recycle synaptic vesicles. In addition, we have identified a number of novel proteins that participate in CCV formation and function at the trans-Golgi network and the plasma membrane. Characterization of two of these proteins, NECAP1 and NECAP2, has led to the identification of a new consensus motif that mediates protein interactions with the clathrin adaptor protein 2. These studies highlight the ability of proteomics to reveal new insights into the mechanisms and functional roles of subcellular compartments.