Proteomic mapping of intercellular synaptic environments via flavin-dependent photoredox catalysis

Abstract

Receptor–ligand interactions play essential signaling roles within intercellular contact regions. This is particularly important within the context of the immune synapse where protein communication at the surface of physically interacting T cells and antigen-presenting cells regulate downstream immune signaling responses. To identify protein microenvironments within immunological synapses, we combined a flavin-dependent photocatalytic labeling strategy with quantitative mass spectrometry-based proteomics. Using α-PD-L1 or α-PD-1 single-domain antibody (VHH)-based photocatalyst targeting modalities, we profiled protein microenvironments within the intercellular region of an immune synapse-forming co-culture system. In addition to enrichment of both PD-L1 and PD-1 with either targeting modality, we also observed enrichment of both known immune synapse residing receptor–ligand pairs and surface proteins, as well as previously unknown synapse residing proteins.