Neurokinin B (NKB) is a member of the tachykinin family of neuropeptides that have neuroinflammatory, neuroimmunological, and neuroprotective functions. In a neuroprotective role, tachykinins can help protect cells against the neurotoxic processes observed in Alzheimer's disease. A change in copper homeostasis is a clear feature of Alzheimer's disease, and the dysregulation may be a contributory factor in toxicity. Copper has recently been shown to interact with neurokinin A and neuropeptide γ and can lead to generation of reactive oxygen species and peptide degradation, which suggests that copper may have a place in tachykinin function and potentially misfunction. To explore this, we have utilized a range of spectroscopic techniques to show that NKB, but not substance P, can bind Cu II in an unusual [Cu II (NKB) 2 ] neutral complex that utilizes two N-terminal amine and two imidazole nitrogen ligands (from each molecule of NKB) and the binding substantially alters the structure of the peptide. Using 1321N1 astrocytoma cells, we show that copper can enter the cells and subsequently open plasma membrane calcium channels but when bound to neurokinin B copper ion uptake is inhibited. This data suggests a novel role for neurokinin B in protecting cells against copper-induced calcium changes and implicates the peptide in synaptic copper homeostasis. KEYWORDS: Neurokinin B, tachykinin, copper, calcium, neurodegeneration, substance P, Fura2, EPR N eurokinin B (NKB, neuromedin K) is a 10 residue peptide that belongs to the tachykinin family of neuropeptides. Other members include the mammalian peptides substance P (SP), neurokinin A (NKA), the Nterminally extended forms of NKA neuropeptide K and neuropeptide γ, and hemokinin.1 The family is characterized by the presence of a common C-terminal sequence FxGLM-NH 2 , which is thought to be important for receptor binding and activation.2 The biological activity of the tachykinin peptides lies with their ability to bind to G protein-coupled receptors and to mediate intracellular calcium release via several signaling pathways, including a G q/11 -coupled pathway, which involves the downstream generation of the second messengers diacylglycerol and IP 3 .2,3 SP, NKA, and NKB bind to neurokinin receptors NK1-R, NK2-R, and NK3-R, and although each peptide can bind to all the receptors, each has a preference for a particular receptor. Thus SP has a preference for NK1-R, NKA for NK2-R, and NKB for NK3-R. The structure of the peptides bound to their receptors is unclear; however, a recent modeling study looking at the interaction of NKB with NK3-R has highlighted not only how the C-terminal conserved domain directs receptor binding but also how the Nterminal residues may be involved in mediating receptor preference. 4 Functionally, the tachykinins are involved in a diverse range of cellular signaling processes including roles in neuroprotection, neuroinflammation, and neurotrophic pathways.