Aggregation and mobility of membrane proteins interplay with local lipid order in the plasma membrane of T cells

To disentangle the elusive lipid–protein interactions in T‐cell activation, we investigate how externally imposed variations in mobility of key membrane proteins (T‐cell receptor [TCR], kinase Lck, and phosphatase CD45) affect the local lipid order and protein colocalisation. Using spectral imaging with polarity‐sensitive membrane probes in model membranes and live Jurkat T cells, we find that partial immobilisation of proteins (including TCR) by aggregation or ligand binding changes their preference towards a more ordered lipid environment, which can recruit Lck. Our data suggest that the cellular membrane is poised to modulate the frequency of protein encounters upon alterations of their mobility, for example in ligand binding, which offers new mechanistic insight into the involvement of lipid‐mediated interactions in membrane‐hosted signalling events.