When Lee clicked the mouse, he got an electron density map in exceptionally sharp focus.
"When you see a map like that, it's like suddenly the wind has kicked up and you're sailing free," Jez says, "because there's this moment, like, before you click that button, no one has ever seen how this protein is put together in three dimensions. You're the first person to ever see it.
"The irony of it is we got such good quality diffraction pattern and electron density maps off such an ugly crystal," he says.
Lock and load
"Once you have the electron density map, the task is to build a structure that matches the amino acid sequence of the protein," Jez says.
"The first thing you do is put in the amino acid backbones and connect them together to form a chain. It's like having a long thread, each inch of which is an amino acid, and your job is to take that thread and move it in three dimensions through that electron density map."
The next step is to add the side chains that make one amino acid different from another, Jez says. "The amino acid sequence is known," he says. "Your goal is to match the way you string together the amino acids in the electron density map to that sequence."
"Once you have the overall structure, you can start to figure out how the enzyme works. The PMT enzyme is trying to join two molecules," Jez says. "To do that, it has to lock them in place so that the chemistry can happen, and then it has to let go of them.
"We think the protein has a lid that opens and closes," he says. "The active site stays open until the substrates enter, and then the lid clamps down, and when it clamps down it actually puts the substrates together."
Calling Bill and Melinda Gates
Not only do infections by Plasmodium falciparum cause the most severe form of malaria, about 40 percent of the human population lives in areas where the parasite is endemic.
|Contact: Diana Lutz|
Washington University in St. Louis