Biologists have discovered that certain proteins vital to life and long thought to be immobilized within the sack-like cell structures where they function instead move freely and rapidly within the structures.
The discovery contradicts widely accepted models for the function of the structures, or organelles, called the Golgi apparatus. There is no obvious explanation for why, despite their movement, the enzymes are not transported out of the organelle, as other mobile proteins are.
Usually, proteins moving within the organelle are eventually packaged in vesicles -- small sacks of membrane -- pinched off and then transported out to the rest of the cell, where they are needed for a variety of purposes.
But these specific proteins are not transported; they are mysteriously retained in the organelle. Without the retention, the organelles would not function properly and vital life processes would break down.
Scientists had proposed that the proteins are anchored and immobilized in the organelle, so that they could perform their essential functions.
The new findings, however, show just the opposite.
"They are milling all around," said Michael Edidin, a Johns Hopkins University biologist involved in the research.
The findings are detailed in a paper published Aug. 9 in the journal Science. And the rapid protein motion can be viewed in a video clip to be posted on the Internet, at the following address: http://www.uchc.edu/htterasaki/flip.html
The researchers were able to study the movement of proteins through a revolutionary technique that uses light-emitting, or fluorescent, molecules taken from a jellyfish, Aequorea victoria. DNA from the jellyfish's fluorescent protein is fused with the DNA of proteins biologists want to study, making them fluorescent.