Developing an Affinity-Based Chemical Proteomics Method to In Situ Capture Amorphous Aggregated Proteome and Profile Its Heterogeneity in Stressed Cells.

Stress induced amorphous proteome aggregation is a hallmark for diseased cells, with the proteomic composition intimately associated with disease pathogenicity. Due to its particularly dynamic, reversible, and dissociable nature, as well as lack of specific recognition anchor, it is difficult to capture aggregated proteins in situ . In this work, we develop a chemical proteomics method (AggLink) to capture amorphous aggregated proteins in live stressed cells and identify the proteomic contents using LC-MS/MS. Our method relies on an affinity-based chemical probe (AggLink 1.0) that is optimized to selectively bind to and covalently label amorphous aggregated proteins in live stressed cells. Especially, chaotrope-compatible ligation enables effective enrichment of labeled aggregated proteins under urea denaturation and dissociation conditions. Compared to conventional fractionation-based method to profile aggregated proteome, our method showed improved enrichment selectivity, detection sensitivity, and identification accuracy. In HeLa cells, the AggLink method reveals the constituent heterogeneity of aggregated proteome induced by inhibition of pro-folding (HSP90) or pro-degradation (proteasome) pathway, which uncovers a synergistic strategy to reduce cancer cell viability. In addition, the unique fluorogenicity of our probe upon labeling aggregated proteome detects its cellular location and morphology. Together, the AggLink method may help to expand our knowledge of the previously nontargetable amorphous aggregated proteome.