Abstract
The cell surface is a dynamic interface that controls cell-cell communication and signal transduction relevant to organ development, homeostasis and repair, immune reactivity, and pathologies driven by aberrant cell surface phenotypes. The spatial organization of cell surface proteins is central to these processes. High-resolution fluorescence microscopy and proximity labeling have advanced studies of surface protein associations, but the spatial organization of the complete surface proteome remains uncharted. In this study, we systematically mapped the surface proteome of human T-lymphocytes and B-lymphoblasts using proximity labeling of 85 antigens, identified from over 100 antibodies tested for binding to surface-exposed proteins. These experiments were coupled with an optimized data-independent acquisition mass spectrometry workflow to generate a robust dataset. Unsupervised clustering of the resulting interactome revealed functional modules, including well-characterized complexes such as the T-cell receptor and HLA class I/II, alongside novel clusters. Notably, we identified mitochondrial proteins localized to the surface, including the transcription factor TFAM, suggesting previously unappreciated roles for mitochondrial proteins at the plasma membrane. A high-accuracy machine learning classifier predicted over 6,000 surface protein associations, highlighting functional associations such as IL10RB's role as a negative regulator of type I interferon signaling. Spatial modeling of the surface proteome provided insights into protein dispersion patterns, distinguishing widely distributed proteins, such as CD45, from localized antigens, such as CD226 pointing to active mechanisms of regulating surface organization. This work provides a comprehensive map of the human surfaceome and a resource for exploring the spatial and functional dynamics of the cell membrane proteome.