Prion Protein's Possible Protective Role

The function of prion protein (PrP) is not known, but a study by Glenn L. Millhauser and coworkers at the University of California, Santa Cruz, suggests it may have a redox-protective role (J. Am. Chem. Soc. 2007, 129, 15440).

PrP is a natural protein that becomes misfolded and aggregated in mad cow disease, Creutzfeldt-Jakob disease, and related conditions. The protein molecules can each bind several Cu(II) ions, and they adopt different coordination modes as additional Cu(II) ions bind.

But in the brain, where most PrP is found, there's a lot more Zn(II) than Cu(II). Millhauser and coworkers looked at what happens to PrP when Cu(II) and Zn(II) are present at levels found in the brain. They found that Zn(II) never displaces Cu(II) from PrP, supporting PrP's role as a Cu(II)-binding protein. But Zn(II) does modulate the way PrP binds Cu(II), causing a shift from a Cu(II) redox-active binding mode to a Cu(II) redox-inactive binding mode.

The researchers propose that PrP's natural role is to protect against Cu(II)'s redox activity, which can cause cellular damage.