Cellular processes, such as when to multiply, are often regulated by switches that control the frequency and timing of interactions between proteins. North Carolina State University scientists have discovered the way in which a specific protein-protein interaction prevents the cell from turning one of its switches off, leading to uncontrolled cell proliferation – one of the hallmarks of cancer.
In a paper published in the December 2007 edition of the Cell Press journal Structure, the NC State researchers show for the first time that the interaction between a rogue version of a specific protein called Ras and its binding partner protein Raf can block the switch from being turned off.
The paper shows, says Dr. Carla Mattos, NC State associate professor of structural and molecular biochemistry and the lead author of the paper, that Raf secures one of the two so-called switch regions in Ras, so that the second switch can act like a closed door that isolates the key area where the overall signal switch is located. Mattos likens the abnormal protein-protein interaction to having the light permanently stuck on because the switch is inaccessible behind the closed door.
In the world of molecular biochemistry, Mattos explains, instructions for the proliferation of cells are given by cascades of protein-protein interactions controlled by on-off switches. The switch is on when the proteins can interact – resulting in cell proliferation – and off when they cannot. If access to the switch is blocked and the switch is stuck on, cells begin to multiply incessantly.
There are 20 existing amino acids that can be joined into chains that make up proteins. Each protein has a unique sequence of amino acids. In the chain of 189 amino acids of which Ras is composed, the position in question is at the 61st amino acid, which is normally a glutamine known to help in turning the interaction switch off. Change, or mutation, of this amino acid to an amino acid called leucine is a commonly observed defect in cancer cells.
"The switch only gets stuck on when Raf is present and the defective Ras has position 61 as a leucine or one of the few amino acids shown to cause cell transformation, one of the properties observed in cancer," Mattos says. "For glutamine or the mutations that do not cause cell transformation, the molecular door can fly open and allow access to the switch – even when Raf is bound to Ras. The door can always open in the absence of Raf."
The paper responds to a paradox that arose in the 1980s when scientists compared the behavior of Ras mutants in cells versus in solution, isolated from other cellular components including Raf. The studies of Ras in solution suggested nothing special about the mutations that cause cell transformation versus those that do not, as any amino acid other than glutamine at position 61 made turning off the Ras switch only 10 times slower, rather than blocking the switch. Scientists did not understand why the isolated Ras mutants behaved differently than the Ras mutants in their cellular environment.
Mattos, research associate Greg Buhrman and undergraduate student Glenna Wink provide the answer to this paradox by showing that the switch stays on when Raf binds Ras containing the leucine mutation and that it can be turned off in the absence of Raf, although not at the normal rate. In normal Ras the switch can be turned off either in the presence or absence of Raf. The atomic resolution structures of the rogue Ras proteins with strongly transforming mutations show that they all keep the molecular door closed and the switch on in the same way. The structures of the normal Ras and of a mutant known to have weak transforming ability both have the molecular door open.
"We all knew that there had to be something in the cell not accounted for by the studies in isolated Ras," Mattos says. "We now know that at least part of that something is the Raf protein. When the defective Ras encounters Raf, the switch becomes inaccessible and the highly controlled cell proliferation system is broken, leading to uncontrolled cell proliferation and cancer."
The study was funded by the National Institutes of Health.
Dr. Carla Mattos | EurekAlert!
Russian scientists show changes in the erythrocyte nanostructure under stress
22.02.2019 | Lobachevsky University
How the intestinal fungus Candida albicans shapes our immune system
22.02.2019 | Exzellenzcluster Präzisionsmedizin für chronische Entzündungserkrankungen
An international research team including astronomers from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has combined radio telescopes from five continents to prove the existence of a narrow stream of material, a so-called jet, emerging from the only gravitational wave event involving two neutron stars observed so far. With its high sensitivity and excellent performance, the 100-m radio telescope in Effelsberg played an important role in the observations.
In August 2017, two neutron stars were observed colliding, producing gravitational waves that were detected by the American LIGO and European Virgo detectors....
Up to now, OLEDs have been used exclusively as a novel lighting technology for use in luminaires and lamps. However, flexible organic technology can offer much more: as an active lighting surface, it can be combined with a wide variety of materials, not just to modify but to revolutionize the functionality and design of countless existing products. To exemplify this, the Fraunhofer FEP together with the company EMDE development of light GmbH will be presenting hybrid flexible OLEDs integrated into textile designs within the EU-funded project PI-SCALE for the first time at LOPEC (March 19-21, 2019 in Munich, Germany) as examples of some of the many possible applications.
The Fraunhofer FEP, a provider of research and development services in the field of organic electronics, has long been involved in the development of...
For the first time, an international team of scientists based in Regensburg, Germany, has recorded the orbitals of single molecules in different charge states in a novel type of microscopy. The research findings are published under the title “Mapping orbital changes upon electron transfer with tunneling microscopy on insulators” in the prestigious journal “Nature”.
The building blocks of matter surrounding us are atoms and molecules. The properties of that matter, however, are often not set by these building blocks...
Scientists at the University of Konstanz identify fierce competition between the human immune system and bacterial pathogens
Cell biologists from the University of Konstanz shed light on a recent evolutionary process in the human immune system and publish their findings in the...
Laser physicists have taken snapshots of carbon molecules C₆₀ showing how they transform in intense infrared light
When carbon molecules C₆₀ are exposed to an intense infrared light, they change their ball-like structure to a more elongated version. This has now been...
11.02.2019 | Event News
30.01.2019 | Event News
16.01.2019 | Event News
22.02.2019 | Physics and Astronomy
22.02.2019 | Materials Sciences
22.02.2019 | Life Sciences