Fig. 5.

Schematic representation of the enrichment of secreted proteins by proximity labeling in cell culture or animals. ① Biotin ligases (BioID, TurboID, miniTurbo) are targeted to the secretory pathway, for example, by tagging the translocon SEC61 in the endoplasmic reticulum (ER) membrane or by targeting to the ER lumen using a transfection or viral transduction strategy. In the ER, secretory proteins are biotinylated prior to their secretion into the extracellular space (cell culture medium or plasma). ② Biotinylated proteins can then be enriched using streptavidin affinity purification. ③ Bead-bound proteins are digested and the resulting peptide samples are ④ analyzed by LC-MS/MS.