Scientists identified a link between the ion transport protein ZIP7 and the cell’s protein degradation system, the proteasome. This discovery provides a promising avenue for treating diseases caused by protein misfolding, such as Alzheimer’s and Parkinson’s.
This is a story about proteins, how they malfunction, and what cells do to prevent that. Credit: Matt Perko, UC Santa BarbaraFor 35 years, Montell’s lab has studied the movement of cells in fruit fly ovaries.
Proteasomes grind up misfolded proteins tagged for recycling, but the enzyme Rpn11 must first remove that tag so the protein can fit. Credit: Xiaoran Guo and Morgan Mutch et al. But proteins will sometimes misfold even in a healthy cell. Fortunately, cells have a quality control system to deal with this eventuality. If the error is small, the cell can try folding it again. Otherwise, it will tag the misfolded molecule with a small protein called ubiquitin and send it out of the endoplasmic reticulum for recycling.
What’s more, the misfolded protein she used, called rhodopsin, contains no zinc in its structure. This led Guo to suspect that ZIP7 must be involved somewhere in the degradation pathway. Co-lead author, and fellow doctoral student, Morgan Mutch used a drug to block the proteasome from degrading misfolded rhodopsin and observed that this negated the beneficial effect of ZIP7. She concluded that ZIP7 must be acting somewhere before the proteasome munches up the misfolded protein.
Mutch determined that ZIP7 was critical in supplying zinc to Rpn11, enabling it to trim the tags that label defective proteins so that they fit into the structure that actually breaks them down. Blocking the Rpn11 enzyme confirmed this hypothesis.
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