By Sean Henahan, Access Excellence

BALTIMORE (August 13, 1996) Proteins vital to life and long thought to be immobilized within the sack-like cell structures of the Golgi apparatus do in fact move freely and rapidly within the structures, report researchers at Johns Hopkins. The discovery contradicts widely accepted models for the function of the Golgi apparatus.

Image: Proteins, now you see 'em...

The researchers studied the movement of proteins by using a novel 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. Then, the researchers used special laser-operated microscopes to follow the movement of the proteins inside the cell.

Scientists have long believed that the proteins are anchored and immobilized in the organelle, so that they could perform their essential functions.The new study shows just the opposite.

"They are milling all around," said Michael Edidin, a Johns Hopkins University biologist involved in the research.

The Golgi apparatus processes and packages molecules needed for a multitude of functions. The biologists were surprised to discover that the proteins move fast enough to traverse the organelle within a few seconds. At that speed, they should easily be taken up by vesicles and transported outside of the Golgi apparatus.

The new oservations raise numerous questions. 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.

"How Golgi membranes maintain their identity amidst this rapid diffusion of resident components now needs to be explained," said the senior author of the paper, Jennifer Lippincott-Schwartz, from the National Institutes of Health.

Related information on the Internet

http://science-mag.aaas.org/science/scripts/display/short/273/5276/797.htm>Science article

Dr. Teraski's Home Page, with video clips of moving proteins.

Teaching Activity: Travel Brochure for a Cell

The Virtual Cell