Photo-proximity labeling in live primary neurons identifies an AMPA-receptor signal transducer in homeostatic synaptic plasticity.

To investigate the molecular basis of homeostatic synaptic plasticity, we adapted a photo-proximity labeling-based functional proteomics workflow to identify protein-protein interactions involving the GluA1 subunit of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) in live primary rat neurons. Using antibodies conjugated to a photoactivatable flavin-based catalyst, we demonstrated target selective biotinylation and recovery of AMPAR along with both well-described and previously unreported auxiliary proteins associated with neurotransmission. This resulted in the identification of the calcium sensor neuronal calcium sensor 1 (NCS1), which we validated and functionally characterized as a key regulator of homeostatic plasticity initiated via engagement with the calcium-permeable AMPARs.