Receptor-proximal phosphoform organization precedes β2 integrin activation

Receptor-proximal phosphoform organization near leukocyte β2 integrins persists during sustained activation, with 95.9% of proteins unchanged while 31% of phosphosites shift.

• Why it matters: It addresses whether receptor-proximal membrane regions are already organized in composition and phosphorylation state before stimulation, or whether organization only emerges after activation.
• What they did: Using CD18-APEX2 proximity labeling with a spatial membrane reference, the study quantified proteins and 4,564 phosphosites near leukocyte β2 integrins at rest and during sustained activation, applying parent-protein correction.
• The result: At rest, 32% of phosphosites deviated significantly from the distribution center and 56% of multi-site proteins diverged beyond measurement error; during activation, spatial phosphoform organization largely persisted, implying signaling can tune pre-existing molecular states without extensive protein redistribution.

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