Disordered protein LAT encodes relative levels of signaling pathways in T cell activation [Perturb-CITE-seq]

Conserved sequence motifs for protein interactions, along with charge distribution, are critical sequence features, and contribute to interpretation of human genetic variation in LAT. While mutant defect severity spans from moderate to complete loss of function, nearly all defective mutants, irrespective of their position in LAT, confer balanced defects across the NFAT and AP-1 pathways. To understand the molecular basis for this observation, we performed proximal protein labeling, which demonstrated that disruption of LAT interaction with a single partner protein indirectly disrupts other partner interactions, likely through the dual roles of these proteins as effectors of downstream pathways and bridging factors between LAT molecules.

Overall, we report widely distributed functional regions throughout a disordered adapter and a precise physical organization of LAT and interacting molecules which constrains signaling outputs. More broadly, we describe an approach for interrogating sequence-function relationships for proteins with complex activities across regulatory layers of the cell.