Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Mutant biological machine makes proteins but can’t let go

28.05.2004


Finding overturns long held ideas about how cells build proteins



Writing in the May 28 issue of Cell, Johns Hopkins researchers report that four critical components of cells’ protein-building machine don’t do what scientists had long assumed.
The machine, called the ribosome, is a ball of RNA (DNA’s cousin) surrounded by proteins. In the RNA center, genetic instructions are read, the right protein building block is added onto a growing chain, and at the appropriate time the chain is snipped and released.

But while researchers have long known that the ribosome builds proteins, little is understood about exactly how it adds to growing proteins and how it releases the finished product.



In the hunt for these details, scientists have focused on four RNA building blocks, or nucleotides, deep within the machine that are identical in every species, from bacteria to humans. Because they sit where the protein chain is actually built, these "universally conserved" nucleotides in the ribosome were thought to help that process.

Unexpectedly, Johns Hopkins researchers have discovered that these four nucleotides are not important for building the protein, but instead help release the finished product. In laboratory experiments, the researchers found that ribosomes with these key spots changed could put proteins together as well as normal ribosomes, but let go of the finished product much more slowly.

"Most scientists have said that these four nucleotides must be critical for synthesis of the growing protein because of their location, and we fully expected that our studies would prove that to be true," says Rachel Green, Ph.D., associate professor of molecular biology and genetics and a Howard Hughes Medical Institute associate investigator. "We were shocked that they appear to play very little if any role in building proteins, and instead normally speed the protein’s release at the right time.

"Our finding underscores the idea that if you build a well-defined system to study a biologic question, you’ll get answers you didn’t expect," adds Green.

Instead of validating existing ideas about the role played by these conserved nucleotides, the researchers’ work suggests a brand new model, says Green. The ribosome actually has another set of evolutionarily unchanged nucleotides, slightly farther from its "business end." Green and her colleagues believe these nucleotides are really responsible for catalyzing the protein’s construction, simply by properly orienting the new building block and the chain, an idea they are testing now.

For the current study, graduate student Elaine Youngman first created 12 mutant ribosomes -- the 12 singly changed alternatives to the natural ribosome. (Four nucleotide building blocks are used to make RNA. Each mutant had one of the four conserved nucleotides replaced with one of its three alternatives.)

Then Youngman tested the ability of each of the purified mutant ribosomes to add a molecule called puromycin onto a growing protein chain. Puromycin looks and acts like a normal protein building block, or amino acid, ready for protein synthesis. However, each amino acid normally used by the ribosome has an identifying RNA "tag," which puromycin almost entirely lacks.

"We had hoped to see one of the mutants really stand out as being incapable of doing this reaction," says Green. "But instead, none of the mutants could do it efficiently, which left us scratching our heads."

So the researchers tested the ribosomes’ ability to use their normal starting materials: actual amino acids attached to their correct RNA tag. Much to the researchers’ surprise, the mutant ribosomes performed perfectly.

"The key difference between puromycin and the real amino acids used in this reaction is that puromycin lacks the RNA tag," says Green. "Researchers use puromycin all the time to study ribosome function, for many good reasons. But now we know ribosomes don’t always treat this molecule as they would real amino acids."

As a result, she says, scientists should carefully evaluate whether the use of puromycin could have skewed interpretation of their experiments.

Amino acids’ RNA tags, called transfer RNA or tRNA, help the ribosome identify the right amino acid to add to the protein, since it matches itself to the genetic instructions (messenger RNA) the ribosome is reading. But the tRNA also acts as a handle for the small amino acid: Specific parts of the tRNA are "held" by other evolutionarily unchanged nucleotides in the ribosome as the amino acid is added onto the protein. Green points out that these nucleotides quite likely position the amino acid properly to catalyze what is already a pretty easy reaction.


The scientists were funded by the National Institute of General Medical Sciences and the Howard Hughes Medical Institute. Authors on the paper are Biochemistry and Molecular Biology graduate student Youngman, Green, laboratory technician Julie Brunelle and undergraduate student Anna Kochaniak, all of Johns Hopkins.

Joanna Downer | EurekAlert!
Further information:
http://www.cell.com
http://www.hopkinsmedicine.org/

More articles from Life Sciences:

nachricht Scientists unlock ability to generate new sensory hair cells
22.02.2017 | Brigham and Women's Hospital

nachricht New insights into the information processing of motor neurons
22.02.2017 | Max Planck Florida Institute for Neuroscience

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Microhotplates for a smart gas sensor

22.02.2017 | Power and Electrical Engineering

Scientists unlock ability to generate new sensory hair cells

22.02.2017 | Life Sciences

Prediction: More gas-giants will be found orbiting Sun-like stars

22.02.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>