Corporate Banner
Satellite Banner
Technology
Networks
Scientific Communities
 
Become a Member | Sign in
Home>News>This Article
  News
Return

Team Discovers Structure of Protein Essential for Quality Control, Nerve Function

Published: Monday, January 21, 2013
Last Updated: Monday, January 21, 2013
Bookmark and Share
Scientists at The Scripps Research Institute have determined the structure of Ltn1, a recently discovered “quality-control” protein that is found in the cells of all plants, fungi and animals.

Ltn1 appears to be essential for keeping cells’ protein-making machinery working smoothly. It may also be relevant to human neurodegenerative diseases, for an Ltn1 mutation in mice leads to a motor-neuron disease resembling amyotrophic lateral sclerosis (ALS, also known as Lou Gehrig’s disease). 

“To better understand Ltn1’s mechanism of action, we needed to solve its structure, and that’s what we’ve done here,” said The Scripps Research Institute (TSRI) Associate Professor Claudio Joazeiro. 

“In addition, this project has brought us a set of structural analysis techniques that we can apply to other exciting problems in biology,” said TSRI Professor Bridget Carragher.

Joazeiro and Carragher, along with Clint Potter, also a TSRI professor, are senior authors of the new report, which appears in the online Early Edition of the Proceedings of the National Academy of Sciences the week of January 14, 2013.

Links to Neurodegenerative Disease 
Ltn1 first turned up on biologists’ radar screens several years ago when a joint Novartis-Phenomix research team noted that mice with an unknown gene mutation were born normal but suffered from progressive paralysis. The scientists dubbed the animals lister mice, because they listed to one side as they walked. Collaborating with Joazeiro, the Novartis team reported in a 2009 paper that the mutated gene normally codes for a type of enzyme known as an E3 ubiquitin ligase, and that the mouse phenotype was due to a neurodegenerative syndrome resembling ALS.

In a study published in the journal Nature the following year, Joazeiro and his postdoctoral research associate Mario H. Bengtson found that the enzyme serves as a crucial quality-control manager for the cellular protein-making factories called ribosomes. Occasionally a ribosome receives miscoded genetic instructions and produces certain types of abnormal proteins, known as “nonstop proteins”— jamming the ribosomal machinery like a wrinkled sheet of paper in an office printer. Bengtson and Joazeiro found that Ltn1 fixes jammed ribosomes by tagging nonstop proteins with ubiquitin molecules, thereby marking them for quick destruction by roving cellular garbage-disposers called proteasomes. 

“The question for us then was, “How does Ltn1 do this?’ ” said Joazeiro. 

Pushing the Boundaries of Electron Microscopy
To help find out, he began a collaboration with Carragher and Potter, who run the National Resource for Automated Molecular Microscopy (NRAMM), an advanced electron microscope facility at TSRI that is funded by the National Institutes of Health’s National Center for Research Resources.

Ltn1 was deemed too large for its structure to be determined by current nuclear magnetic resonance (NMR) technology, and, as the scientists know now, too flexible to allow the highly regular crystalline packing needed by X-ray crystallographers. “It’s a very floppy molecule, so it would be hard to crystallize,” said Potter. 

Advanced electron microscopy offered a way, however. Dmitry Lyumkis, a graduate student in the NRAMM laboratory and first author of the study, took high-resolution images of yeast Ltn1 with an electron microscope. He then used sophisticated image and data processing software to align and average individual images. The technique eliminates much of the random “noise” that obscures single images and produces a sharp 3D picture of the protein.

No one has ever used electron microscopy to distinguish so many—more than 20—conformations of such a small protein. “Usually electron microscopists determine no more than two or three conformational states, and they work with protein complexes whose size is in the megadalton range, but Ltn1 is only 180 kilodaltons, an order of magnitude smaller,” Lyumkis said.

An Unusually Flexible Structure
The analysis revealed that Ltn1 has an elongated, double-jointed and extraordinarily flexible structure with two working ends—the N-terminus and C-terminus. “We anticipate that the N-terminus is responsible for association with the ribosome and know that the C-terminus is responsible for the ubiquitylation of nonstop proteins,” said Lyumkis. “We suspect that the high flexibility of this structure is needed for it to work on the variety of nonstop proteins that can get stuck in ribosomes.”

One of the next steps for the team is to evaluate Ltn1’s individual segments, which appear to be more rigid, using X-ray crystallography, in order to develop a piece-by-piece atomic-resolution model of the enzyme. Another is to determine the structure of Ltn1 when it is attached to a ribosome and operating on a nonstop protein. Joazeiro notes that a typical yeast cell has nearly 200,000 ribosomes but requires only 200 Ltn1 copies for adequate quality control under normal growth conditions. “Somehow this enzyme can efficiently sense which ribosomes are jammed, and we expect that by solving the joint structure of Ltn1 and a ribosome, we’ll be able to understand how it does this,” he says.

Lyumkis, Carragher, Potter and their colleagues at NRAMM also plan to use a similar electron microscopy-based approach to find the structures of other important proteins with highly variable “heterogeneous” conformations. “Heterogeneity has been a big challenge,” said Potter, “and being able to collect this large dataset and do all of this data processing successfully has been a critical breakthrough.”

Other contributors to the paper, “Single-particle EM reveals extensive conformational variability of the Ltn1 E3 ligase,” were Selom K. Doamekpor and Christopher D. Lima at the Sloan–Kettering Institute; Tasha B. Toro and Matthew D. Petroski of the Sanford-Burnham Medical Research Institute; and Mario H. Bengtson and Joong-Won Lee of TSRI. For more information on the paper, see http://intl.pnas.org/content/early/2013/01/10/1210041110.abstract.

The study was supported by grants from the National Center for Research Resources (RR017573); the National Institute of General Medical Sciences (GM103310); the National Institutes of Health (R01 GM083060, R01 NS075719, GM061906); and the American Cancer Society (RSG-11-224-01-DMC, RSG-08-298-01-TBE).


Further Information

Join For Free

Access to this exclusive content is for Technology Networks Premium members only.

Join Technology Networks Premium for free access to:

  • Exclusive articles
  • Presentations from international conferences
  • Over 3,000+ scientific posters on ePosters
  • More Than 4,500+ scientific videos on LabTube
  • 35 community eNewsletters


Sign In



Forgotten your details? Click Here
If you are not a member you can join here

*Please note: By logging into TechnologyNetworks.com you agree to accept the use of cookies. To find out more about the cookies we use and how to delete them, see our privacy policy.

Related Content

Breakthrough Approach to Breast Cancer Treatment
Scripps scientists have designed a drug candidate that decreases growth of breast cancer cells.
Tuesday, May 24, 2016
Making Genetic Data Easier to Search
Scripps team streamlines biomedical research by making genetic data easier to search.
Tuesday, May 17, 2016
Potent Therapeutic 'Warheads' That Target Cancer Cells
Scripps scientists have developed molecular “warheads” that could be used to treat cancer.
Tuesday, May 17, 2016
Predicting Cell Changes that Affect Breast Cancer Growth
Researchers find small structural changes in a key breast cancer receptor that can predict cancer growth.
Tuesday, May 03, 2016
Secrets of a Deadly Virus Family Revealed
Scripps Research scientists uncover the glycoprotein structure of LCMV. The findings could guide development of treatments for Lassa fever.
Wednesday, April 27, 2016
First ‘Teenage’ HIV-Neutralizing Antibody Discovered
Scientists have studied the evolution of anti-HIV antibodies, with hopes of creating a vaccine to prevent AIDS.
Wednesday, April 06, 2016
Discovering 'Outlier' Enzymes
Researchers at TSRI and Salk Institute have discovered 'Outlier' enzymes that could offer new targets to treat type 2 diabetes and inflammatory disorders.
Saturday, April 02, 2016
Encouraging Foundation for Upcoming AIDS Vaccine Clinical Trial
Engineered vaccine protein binds key immune cells that exist in nearly everyone.
Tuesday, March 29, 2016
New Approach to Curbing Cancer Cell Growth
Using a new approach, scientists at The Scripps Research Institute (TSRI) and collaborating institutions have discovered a novel drug candidate that could be used to treat certain types of breast cancer, lung cancer and melanoma.
Monday, March 14, 2016
Vaccine Against Dangerous Designer Opioids
With use of synthetic opioid "designer drugs" on the rise, scientists from The Scripps Research Institute (TSRI) have a new strategy to curb addiction and even prevent fatal overdoses.
Thursday, February 18, 2016
Potential Target for Treatment of Autism
Grant of $2.4 million will support further research.
Friday, October 02, 2015
Key Morphine Regulator Identified
The findings could lead to less addictive pain medications.
Thursday, September 24, 2015
$6 Million Awarded to Develop Alternative HIV/AIDS Vaccine
Scientists from the Florida campus of The Scripps Research Institute (TSRI) have been awarded up to nearly $6 million from the Bill & Melinda Gates Foundation to develop a revolutionary HIV/AIDS alternative vaccine that has demonstrated great potential in animal models.
Thursday, September 24, 2015
Novel Role of Mitochondria in Immune Function Identified
Scientists at The Scripps Research Institute (TSRI) have discovered a new role for an enzyme involved in cell death.
Monday, September 21, 2015
Scientists Make Strides in Therapy Preventing Addiction Relapse
Single Injection of Drug Candidate Prevents Meth Relapse in Animal Models.
Thursday, August 06, 2015
Scientific News
The Rise of 3D Cell Culture and in vitro Model Systems for Drug Discovery and Toxicology
An overview of the current technology and the challenges and benefits over 2D cell culture models plus some of the latest advances relating to human health research.
Scientists Find Evidence That Cancer Can Arise Changes
Researchers at Rockefeller University have found a mutation that affects the proteins that package DNA without changing the DNA itself can cause a rare form of cancer.
Developing a More Precise Seasonal Flu Vaccine
During the 2014-15 flu season, the poor match between the virus used to make the world’s vaccine stocks and the circulating seasonal virus yielded a vaccine that was less than 20 percent effective.
A Peachy Defense System for Seeds
ETH chemists are developing a new coating method to protect seeds from being eaten by insects. In doing so, they have drawn inspiration from the humble peach and a few of its peers.
Fighting Cancer with Borrowed Immunity
A new step in cancer immunotherapy: researchers from the Netherlands Cancer Institute and University of Oslo/Oslo University Hospital show that even if one's own immune cells cannot recognize and fight their tumors, someone else's immune cells might.
Modified Microalgae Converts Sunlight into Valuable Medicine
A special type of microalgae can soon produce valuable chemicals such as cancer treatment drugs and much more just by harnessing energy from the sun.
Breakthrough Approach to Breast Cancer Treatment
Scripps scientists have designed a drug candidate that decreases growth of breast cancer cells.
Loss Of Y Chromosome Increases Risk Of Alzheimer’s
Men with blood cells that do not carry the Y chromosome are at greater risk of being diagnosed with Alzheimer’s disease. This is in addition to an increased risk of death from other causes, including many cancers. These new findings by researchers at Uppsala University could lead to a simple test to identify those at risk of developing Alzheimer’s disease.
Making Virus Sensors Cheap and Simple
Researchers at The University of Texas at Austin demonstrated the ability to detect single viruses in a solution containing murine cytomegalovirus (MCMV).
A Guide to CRISPR Gene Activation
A comparison of synthetic gene-activating Cas9 proteins can help guide research and development of therapeutic approaches.
Scroll Up
Scroll Down
Skyscraper Banner

Skyscraper Banner
Go to LabTube
Go to eposters
 
Access to the latest scientific news
Exclusive articles
Upload and share your posters on ePosters
Latest presentations and webinars
View a library of 1,800+ scientific and medical posters
3,000+ scientific and medical posters
A library of 2,500+ scientific videos on LabTube
4,500+ scientific videos
Close
Premium CrownJOIN TECHNOLOGY NETWORKS PREMIUM FOR FREE!