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 3,300+ scientific posters on ePosters
  • More Than 4,900+ 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

Drug Candidates Reduce Abnormal Protein Production
New drug candidates improve cell ability to catch miss-folded proteins that could cause deadly diseases.
Friday, July 22, 2016
Scientists Link Bipolar Disorder to Unexpected Brain Region
Researchers from The Scripps Research Institute have found that gene within the brain’s striatum could be linked to biopolar disorder.
Wednesday, July 20, 2016
New Cancer Drug Target Found in Dual-Function Protein
Findings from a study from TSRI have shown that targeting a protein called GlyRS might help to halt cancer growth.
Wednesday, June 29, 2016
HIV Structure Stabilized
Findings represent ‘big accomplishment’ in biomedical engineering and design.
Wednesday, June 29, 2016
New Method Opens Door to Development of Many New Medicines
Findings from TSRI reveal human proteins are better drug targets than previously thought.
Friday, June 17, 2016
Harnessing Nature’s Vast Array of Venoms for Drug Discovery
Scripps scientists have developed a method for rapidly identifying venoms.
Wednesday, May 25, 2016
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
Scientific News
Breakthrough Flu Vaccine Inhibited by Pre-existing Antibodies
Universal truths – how existing antibodies are sabotaging the most promising new human flu vaccines.
Researchers Develop Software That Could Facilitate Drug Development
AptaTRACE can identify aptamers, potentially speed drug advancement.
Gene Therapy for Metabolic Liver Diseases
Researchers have tested gene therapy in pigs from hereditary tyrosinemia type 1, with corrected liver cells being transplanted into the diseased liver.
Zika Vaccine Candidates Show Promise
Two experimental vaccines have shown promise against a major viral strain responsible for the Brazilian Zika outbreak.
New Medication Shows Promise Against Liver Fibrosis in Animal Studies
Liver fibrosis is a gradual scarring of the liver that puts people at risk for progressive liver disease and liver failure.
Raw Eggs Deemed Safe to Eat
A report published today by the Advisory Committee on the Microbiological Safety of Food (ACMSF) into egg safety has shown a major reduction in the risk from salmonella in UK eggs.
Monitoring TTX Toxin in Shellfish
In a number of small studies, mussels and oysters from the eastern and northern part of the Oosterschelde in Holland were found to contain tetrodotoxin (TTX).
Gene Terapy for Muscle Wasting Developed
New gene therapy could save millions of people suffering from muscle wasting disease.
NIH Begins Yellow Fever Vaccine Trial
NIH has initiated an early-stage clinical trial of a vaccine to protect against yellow fever.
Gene-Editing 'Toolbox' Targets Multiple Genes Simultaneously
Researchers have designed a system that modifies, or edits, multiple genes in a genome at once while minimising unintentional effects.
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
3,300+ scientific and medical posters
A library of 2,500+ scientific videos on LabTube
4,900+ scientific videos
Close
Premium CrownJOIN TECHNOLOGY NETWORKS PREMIUM FOR FREE!