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 What Makes Stem Cells into Perfect Allrounders
27.06.2017 | Universität Zürich

nachricht Study shines light on brain cells that coordinate movement
26.06.2017 | University of Washington Health Sciences/UW Medicine

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Study shines light on brain cells that coordinate movement

26.06.2017 | Life Sciences

Smooth propagation of spin waves using gold

26.06.2017 | Physics and Astronomy

Switchable DNA mini-machines store information

26.06.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>