The Life Cycle Of Proteins

Red and green flashing proteins may offer the key to understanding proteomics -- the next logical step in human genetics following the mapping of the human genome, scientists said Thursday.

A team at the University of California at San Diego said they had devised a method to watch while proteins work in a cell.

Two teams of researchers announced in 2000 that they had mapped the human genome -- the entire collection of genes. But they found there were only a surprising 30,000 to 40,000 genes.

That meant the genes themselves are not so important, but the proteins they control. The body must be mixing and matching gene activity to make the 250,000 or so proteins that produce the complex organism that is a human being, they said.

So the race was on to figure out what the proteins are doing in the body.

“It's clear that the next big challenge is understanding how the proteins fit together and how they locate themselves and change their location in order to give cells their properties,” said Mark Ellisman, UCSD professor of neurosciences and bioengineering who led the study.

“Proteins operate in teams. They cluster together like little groups of building blocks to form machines that do the work inside of cells,” said Ellisman, whose study was published in Friday's issue of the journal Science.

He and colleagues developed a molecular “tag” made up of a few amino acids, the compounds that make up proteins.

They are designed to fit into target proteins like a piece of a jigsaw puzzle -- and they flash red or green when fluoresced. The tags are even small enough to be used with an electron microscope.

“Just like real estate ... location is important and without the ability to use high resolution technology like electron microscopy, you can't determine the locations precisely enough of these small proteins,” Ellisman said. “This technique allows you to do that.”

The researchers experimented with connexins, proteins found in cell membranes involved in the interactions between adjacent cells. Ellisman's team used the flashing tags to show how and where the connexins moved.

“It's important to understand how the brain works ... how tissues work in health and disease. These techniques are a first big step in making this much, much easier to do,” Ellisman said.