The researchers then cut up YiiP using enzymes and analyzed the resulting pieces in an instrument that helped them identify the makeup of each piece. By comparing those pieces to pieces of YiiP that had not been exposed to hydroxyl radicals, the researchers could tell which segments create the channel.
Using this and other information, the scientists were able to figure out how the protein works.
Outside the membrane is an abundance of protons, with a lower concentration inside the membrane, creating what is known as a concentration gradient. The protons want to flow "down" this gradient into the cell, like water following gravity down a waterfall, says Fu. Thus, when the central pocket of the transporter protein is open to the outside, a proton will bind to the pocket.
"When the protons move from a place of high concentration to low concentration, they generate a force like falling water does," he says. The protein harnesses this force to change its shape, cutting off the pocket's access to the outside environment and opening up its access to the inside. There, the proton will continue its "fall" by unbinding from the pocket and entering the inside space.
Once it has released the proton, the pocket is free to bind to zinc. This binding again changes the protein's shape, shutting off the pocket's access to the inside of the membrane and once again exposing it to the outside. A proton then drives the zinc ion out of the pocket, and the cycle continues.
"Understanding the way the protein works, especially which segments of the prot
|Contact: Shawna Williams|
Johns Hopkins Medicine