Proteomic dissection of large extracellular vesicle surfaceome unravels interactive surface platform.

The extracellular vesicle (EV) surface proteome (surfaceome) acts as a fundamental signalling gateway by bridging intra- and extracellular signalling networks, dictates EVs' capacity to communicate and interact with their environment, and is a source of potential disease biomarkers and therapeutic targets. However, our understanding of surface protein composition of large EVs (L-EVs, 100-800 nm, mean 310 nm, ATP5F1A, ATP5F1B, DHX9, GOT2, HSPA5, HSPD1, MDH2, STOML2), a major EV-subtype that are distinct from small EVs (S-EVs, 30-150 nm, mean 110 nm, CD44, CD63, CD81, CD82, CD9, PDCD6IP, SDCBP, TSG101) remains limited. Using a membrane impermeant derivative of biotin to capture surface proteins coupled to mass spectrometry analysis, we show that out of 4143 proteins identified in density-gradient purified L-EVs (1.07-1.11 g/mL, from multiple cancer cell lines), 961 proteins are surface accessible. The surface molecular diversity of L-EVs include (i) bona fide plasma membrane anchored proteins (cluster of differentiation, transporters, receptors and GPI anchored proteins implicated in cell-cell and cell-ECM interactions); and (ii) membrane surface-associated proteins (that are released by divalent ion chelator EDTA) implicated in actin cytoskeleton regulation, junction organization, glycolysis and platelet activation. Ligand-receptor analysis of L-EV surfaceome (e.g., ITGAV/ITGB1) uncovered interactome spanning 172 experimentally verified cognate binding partners (e.g., ANGPTL3, PLG, and VTN) with highest tissue enrichment for liver. Assessment of biotin inaccessible L-EV proteome revealed enrichment for proteins belonging to COPI/II-coated ER/Golgi-derived vesicles and mitochondria. Additionally, despite common surface proteins identified in L-EVs and S-EVs, our data reveals surfaceome heterogeneity between the two EV-subtype. Collectively, our study provides critical insights into diverse proteins operating at the interactive platform of L-EVs and molecular leads for future studies seeking to decipher L-EV heterogeneity and function.