KYL peptide is an EphA4 receptor tyrosine kinase inhibitor (Kd = 0.8 μM); inhibits EphA4-EphrinA5 interactions (IC50 = 6.34 μM). Prevents AβO induced synaptic damage, dendritic spine loss and prevents the blocking of LTP in hippocampal CA3-CA1 transmissions. Exhibits a long halflife in cell culture media (8 and 12 hours in PC3 and C2C12 media respectively). Neuroprotective.