The Evolution of the Mad Cow
Thanks to Mark Johnson of the Journal Sentinel for blogging about "the quest to find where prions came from." Mark wrote:
Scientists in Canada and the United States claim to have found the evolutionary origin of prions, the deadly killer responsible for a family of fatal brain-wasting illnesses: chronic wasting disease in deer; scrapie in sheep; mad cow disease in cows; and human mad cow disease, kuru and Creutzfeldt-Jakob disease in people.
In each disease, the prion, a misfolded protein, leaves behind the same grim calling card: spongelike holes in otherwise healthy brains.
Now scientists from the University of Toronto, University of California, San Francisco and the University of Alberta say they have found evidence that prions descended from the ancient ZIP family of metal ion transporters. These ZIP proteins are able to transport zinc and other metals across the membranes of cells.
In their paper, published this week in the online journal PLoS ONE, the scientists say they discovered that prion proteins and ZIP proteins contain long stretches of similar amino acid sequences. The scientists calculated that the similar sequences in both ZIP and prion proteins would acquire very similar three-dimensional structures. Finally, ZIP and prion proteins have a number of other factors in common that suggest an evolutionary link, the scientists reported.
