Photoaffinity-engineered protein scaffold for systematically exploring native phosphotyrosine signaling complexes in tumor samples.

Phosphotyrosine (pTyr)-regulated protein complexes play critical roles in cancer signaling. The systematic characterization of these protein complexes in tumor samples remains a challenge due to their limited access and the transient nature of pTyr-mediated interactions. We developed a hybrid chemical proteomics approach, termed Photo-pTyr-scaffold, by engineering Src homology 2 (SH2) domains, which specifically bind pTyr proteins, with both trifunctional chemical probes and genetic mutations to overcome these challenges. Dynamic SH2 domain-scaffolding protein complexes were efficiently cross-linked under mild UV light, captured by biotin tag, and identified by mass spectrometry. This approach was successfully used to profile native pTyr protein complexes from breast cancer tissue samples on a proteome scale with high selectivity, achieving about 100 times higher sensitivity for detecting pTyr signaling proteins than that afforded by traditional immunohistochemical methods. Among more than 1,000 identified pTyr proteins, receptor tyrosine kinase PDGFRB expressed on cancer-associated fibroblasts was validated as an important intercellular signaling regulator with poor expression correlation to ERBB2, and blockade of PDGFRB signaling could efficiently suppress tumor growth. The Photo-pTyr-scaffold approach may become a generic tool for readily profiling dynamic pTyr signaling complexes in clinically relevant samples.