TAT and nervous system disorder: Proteolytic processing of Src to generate the neurotoxic truncated fragment ΔNSrc is also a pathological event directing neuronal death (18), and we demonstrated the substrate-specific calpain inhibitor Tat-Src could protect against neuronal cell loss in vivo (Fig. 6), small-molecule compounds mimicking TAT-Src peptide in specifically blocking calpain cleavage of Src in neurons (Fig. 6) are potential neuroprotective drug candidates to reduce excitotoxic neuronal loss in neurological disorders.