Antibody-Based Proximity Labeling Reveals Bait-Proximal Proteomes in Paraffin-Embedded and Snap-Frozen Tissue Samples.

Proximity-based labeling approaches have proven highly valuable for uncovering protein-protein interactions, yet their application to primary patient material remains challenging. Here, we present a workflow enabling the use of the antibody-based ProtA-Turbo proximity labeling system in both formalin-fixed paraffin-embedded (FFPE) and snap-frozen tissue specimens. Our method efficiently directs biotinylation to diverse antibody baits across tissues of different origins. Downstream mass spectrometry-based proteomics analyses demonstrate the specificity of the method by profiling the proximal proteome of H3K27ac-marked chromatin, the nuclear lamina-associated protein EMD, and the Ser2-phosphorylated POLR2A subunit of RNA polymerase II. Using this method, we identified cell-type-specific factors and transcriptional regulators in salivary gland carcinoma, healthy testis, and testicular cancer tissue sections. The ability to detect disease-associated complexes directly within their native, spatially resolved cellular context using ProtA-Turbo can provide new insights into the molecular basis of human disease and may reveal novel, potentially actionable factors with translational relevance.