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News Release 05-077

Researchers Identify Proteins that Direct Intracellular Transport and Locomotion

Modified microtubules serve as traffic signals

Molecular "tags" on microtubules direct traffic inside cells.

Molecular "tags" on microtubules direct traffic inside cells.


May 13, 2005

This material is available primarily for archival purposes. Telephone numbers or other contact information may be out of date; please see current contact information at media contacts.

Researchers have identified a new group of enzymes that appear to control how cells direct internal traffic and regulate certain types of locomotion, according to a report in the May 12 online edition of the journal Science.

Complex cells—from single-celled fungi to those in humans—are equipped with a sophisticated transportation infrastructure.  Motor proteins haul molecular cargo to and from different locations inside cells by traveling along a network of protein fibers called microtubules. Enzymes inside cells frequently add or remove different molecules from the surfaces of microtubules. And although scientists have known of such modifications for many years, figuring out what these molecular tags do and how they are formed has been difficult—until now.

A team headed by Jacek Gaertig of the University of Georgia, Athens, and Bernard Eddé of the National Center for Scientific Research (CNRS) in France, has identified a group of enzymes responsible for attaching glutamic acid (an amino acid) tags to the sides of microtubules.  The enzymes—known as polyglutamylases—produce glutamic acid chains of varying length and branching patterns, which appear to act like cellular traffic signals, guiding molecular motors as they travel along microtubules.

Eddé's group purified a polyglutamylase complex from mice—a feat Gaertig described as a "biochemical tour de force." Then, Gaertig's group turned to Tetrahymena—a single-celled aquatic creature researchers commonly use in the laboratory—to figure out which parts of the enzymes generate the glutamic acid chains on microtubules and what the enzyme does inside cells.  The team determined that the enzymes target different locations in the organism where they tag specific sites on near-by microtubules. 

One polyglutamylase, for example, acted on cilia—microtubule-rich appendages Tetrahymena uses as "oars" for swimming.  As molecular motors called dynein move along microtubules inside cilia, these oars bend and stroke, propelling the organism forward.  When the team coaxed the organism to over-modify microtubules by increasing levels of polyglutamylase enzymes, the cilia stopped moving.  Apparently, the extra glutamic-acid tags act like a stop sign for regulating dynein.

"The function of these glutamic acid chains have, until now, remained completely obscure," says Eve Barak, manager of the National Science Foundation program that funded Gaertig's work. "The findings are an important step for understanding how cells control intracellular traffic and locomotion."

Gaertig hopes these findings will help unravel other mysteries about intracellular traffic and locomotion such as how  motor proteins know which microtubule "highway" will take them to the proper destination and how fast to travel. 

To read more, see the University of Georgia press release.

-NSF-

Media Contacts
Nicole Mahoney, NSF, (703) 292-8070, email: nmahoney@nsf.gov

Program Contacts
Eve Barak, NSF, (703) 292-7113, email: ebarak@nsf.gov

Principal Investigators
Jacek Gaertig, University of Georgia, Athens, 706 542 3409, email: jgaertig@cb.uga.edu

The U.S. National Science Foundation propels the nation forward by advancing fundamental research in all fields of science and engineering. NSF supports research and people by providing facilities, instruments and funding to support their ingenuity and sustain the U.S. as a global leader in research and innovation. With a fiscal year 2020 budget of $8.3 billion, NSF funds reach all 50 states through grants to nearly 2,000 colleges, universities and institutions. Each year, NSF receives more than 40,000 competitive proposals and makes about 11,000 new awards. Those awards include support for cooperative research with industry, Arctic and Antarctic research and operations, and U.S. participation in international scientific efforts.

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