Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Key regulatory enzyme is a molecular ’octopus’

20.06.2003


After seven years of work, researchers have succeeded in deducing the three-dimensional structure of an elusive and complex protein enzyme that is central to regulating the body’s largest family of receptors. These receptors, called G-protein-coupled receptors, nestle in the cell membrane and respond to external chemical signals such as hormones and neurotransmitters, to switch on cell machinery.



The thousands of such receptors throughout the body play a fundamental role in the mechanisms of sight, smell and taste, and in regulating heart rate, blood pressure and glucose metabolism. The receptors are by far the most common target for drugs that affect cardiac output, blood pressure and many other physiological functions. Thus, said the researchers, their fundamental discovery could guide pharmaceutical companies in creating a new class of drugs that aim not at blocking the receptors themselves, but at modulating the machinery that regulates them. Such drugs could treat a range of disorders from congestive heart failure to Parkinson’s disease, they said.

The newly revealed structure of this receptor "off-switch" -- called a G protein-coupled receptor kinase (GRK) -- reveals the protein as the molecular equivalent of a three-armed octopus, with independent segments capable of performing multiple regulatory functions at once. Kinases are enzymes that act as molecular switches by adding phosphates to other proteins.


The researchers -- led by Howard Hughes Medical Institute investigator Robert Lefkowitz at Duke University Medical Center and John Tesmer of the University of Texas at Austin -- reported their findings in the May 23, 2003, issue of the journal Science. The team also included scientists from the University of Texas at Austin and University College London. Also on the research team was Darrell Capel of Duke.

"Fundamental to the regulation of all these receptors is the ability to damp their signaling in the face of constant stimulation," said Lefkowitz. "Years ago, we had discovered that this down-regulation occurs due to a phosphorylation of the activated receptor that triggers binding of a protein called beta arrestin. This protein stops further G protein signaling and acts as an adaptor and scaffolding that connects to other signaling molecules."

Thus, the cellular "stop signal" not only turns off the G protein, but immediately tags the receptor for recycling into the cell interior and turns on other signaling pathways, said Lefkowitz. His laboratory identified that enzyme as GRK, but a central mystery was how the family of GRK enzymes fulfills their intricate regulatory duties.

In the latest work the researchers deduced the structure of GRK2, the member of the GRK enzyme family that is active in heart muscle and many other tissues.

Critical to solving that mystery was obtaining the three-dimensional structure of GRK2 using X-ray crystallography. In this technique, pure crystals of a protein are bombarded by an intense X-ray beam, and the protein structure is deduced by analyzing the pattern of the beam’s diffraction. This structural determination was done by co-author John Tesmer and his colleagues.

The resulting structure revealed the details of three regions, or domains, of the GRK2 enzyme, which had earlier been identified by biochemical studies in the Lefkowitz laboratory:

  • The central, or catalytic domain is the region that triggers the phosphorylation reaction
  • The "regulator of G protein signaling homology" (RH) domain attaches to the G protein to switch it off, and
  • The "PH" domain enables GRK2 to home in on the G protein at the cell membrane and attach to it.

To reveal how GRK2 interacts with the G protein, the researchers obtained the structure of GRK2 attached to a subunit of the G protein to which it normally binds, or complexes. Lefkowitz noted that a particularly striking achievement was the production of pure crystals of the highly complicated protein complex by Tesmer and his colleagues.

"The results of this prodigious effort were some really striking and unanticipated insights into the structure of the GRK2 complex," said Lefkowitz. "For one thing, the three domains are not aligned in a straight line, but assembled as if they were the three vertices of an equilateral triangle. And their spacing allows them to perform their docking and catalytic functions simultaneously.

"This means that GRK2 could be a remarkably effective and multitasking mechanism for turning off G protein signaling." Thus, he said, the GRK2 is built to bind to the receptor and phosphorylate it, allowing attachment by beta arrestin, and at the same time, bind the G protein to switch it off.

"This structural determination has significance at two levels," concluded Lefkowitz. "First, it gives us important new information about the basic biology of this important regulatory mechanism. And second, it gives us the detailed molecular coordinates of this structure that guide drug developers in designing specific compounds to regulate the enzyme."

Contact: Dennis Meredith, dennis.meredith@duke.edu

Dennis Meredith | EurekAlert!
Further information:
http://www.duke.edu

More articles from Life Sciences:

nachricht MicroRNA helps cancer evade immune system
19.09.2017 | Salk Institute

nachricht Ruby: Jacobs University scientists are collaborating in the development of a new type of chocolate
18.09.2017 | Jacobs University Bremen gGmbH

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

Im Focus: Quantum Sensors Decipher Magnetic Ordering in a New Semiconducting Material

For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.

Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...

Im Focus: Fast, convenient & standardized: New lab innovation for automated tissue engineering & drug

MBM ScienceBridge GmbH successfully negotiated a license agreement between University Medical Center Göttingen (UMG) and the biotech company Tissue Systems Holding GmbH about commercial use of a multi-well tissue plate for automated and reliable tissue engineering & drug testing.

MBM ScienceBridge GmbH successfully negotiated a license agreement between University Medical Center Göttingen (UMG) and the biotech company Tissue Systems...

Im Focus: Silencing bacteria

HZI researchers pave the way for new agents that render hospital pathogens mute

Pathogenic bacteria are becoming resistant to common antibiotics to an ever increasing degree. One of the most difficult germs is Pseudomonas aeruginosa, a...

Im Focus: Artificial Enzymes for Hydrogen Conversion

Scientists from the MPI for Chemical Energy Conversion report in the first issue of the new journal JOULE.

Cell Press has just released the first issue of Joule, a new journal dedicated to sustainable energy research. In this issue James Birrell, Olaf Rüdiger,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

New quantum phenomena in graphene superlattices

19.09.2017 | Physics and Astronomy

A simple additive to improve film quality

19.09.2017 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>