Uptake protein acts as zinc's doorway to the cell

Discovery of mechanism sheds light on how zinc - essential to the growth of all living organisms - enters cells

A study to be published as the paper of the week in the Journal of Biological Chemistry this December details how zinc, an element fundamental to cell growth, enters the cell via zinc-specific uptake proteins. The research, conducted at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory, is the first to purify this kind of protein and study its role in zinc uptake.

Zinc is crucial to the health of all living organisms. At the cellular level, zinc is responsible for cell growth, which in turn affects the health, growth, and reproduction of an organism.

While there are six classes of known proteins that act as transporters or channels enabling zinc to cross the cell membrane, scientists have identified one metal-specific family of proteins whose purpose is to facilitate the cell's zinc uptake. These are called ZIP proteins, a reference to their resemblance to zinc-regulated and ion-regulated transporter proteins.

The exact mechanism by which ZIP proteins facilitate zinc uptake has been a mystery. Brookhaven scientists led by biologist Dax Fu - who have characterised other zinc-specific proteins that maintain healthy levels of zinc on either side of the cell membrane - have now taken a closer look at this process.
A long-held belief has posited that ZIP proteins work like elevators, pumping zinc across the cell membrane and into the cell. However, Fu and his colleagues found no evidence to support this explanation.

''This was a big surprise. For the last fifteen years, the assumption has been that the ZIP protein acts like a pump or elevator,'' said Fu. ''Instead, we have found that ZIP is more like a door.''