Prion and prejudice: normal protein and the synapse.

The word prion has become synonymous with unusual diseases, such as bovine spongiform encephalopathy and Creutzfeldt-Jakob disease. However, there is also a normal prion protein that does not cause disease. Until recently this highly conserved and widely expressed glycoprotein has been overshadowed by its rogue isoform. Now it is emerging that not only is this protein important for understanding prion disease but it is also important for a healthy brain. The normal cellular isoform of the prion protein is expressed at high levels at synapses suggesting an important role in neuronal function. There is increasing evidence that the normal prion protein binds copper and the resulting complex possesses anti-oxidant activity, and that this, in turn, might have vital implications for synaptic homeostasis.