Kinase activity of FYN is needed for tyrosine phosphorylation of the GRIN2B (also known as NR2B or GluN2B) subunit of the NMDA receptor complex in response to BDNF-mediated activation of the NTRK2 (TRKB) receptor (Mizuno et al. 2003, Li et al. 2017). The exact stoichiometry of this reaction and involvement of other proteins is not known.
Based on studies in rats, phosphorylation of GRIN2B by FYN downstream of NTRK2 signaling plays an important role in long term potentiation (LTP) and spatial memory formation (Mizuno et al. 2003) as well as in spinal LTP and pain hypersensitivity after peripheral nerve injury (Li et al. 2017).