For several years, scientists have been pondering a question about a genetic disease called Charcot-Marie-Tooth (CMT) disease type 2D: how can different types of mutations, spread out across a gene, produce the same condition?
Now, a team of scientists at The Scripps Research Institute may have found the answer. By studying a gene called GARS, which is mutated in individuals with the disease, the team found that all the mutations have one thing in common: they cause the tightly coiled three-dimensional shape of the resulting protein to shift open.
The more open configuration creates a space for other proteins to bind, causing havoc. "That is the basis for potential disease-causing interactions," said Scripps Research Associate Professor Xiang-Lei Yang, senior author of the study, "but also for potential therapeutic intervention." It is possible that scientists could develop drugs to fit into the open area, blocking its access to other proteins.
The findings, to be published this week in the online issue of Proceedings of the National Academies of the Sciences (PNAS) help scientists explain how CMT type 2D occurs. The results may also have implications for other diseases, such as amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease.
A Puzzling Disease
Named after the three physicians who first reported the disease in 1886, CMT is the most common inherited neurological disorder, estimated to affect one in 2,500 people. Although it is not fatal, CMT causes progressive weakness and wasting of muscles in the feet, legs, hands, and forearms by striking down the nerves that reach down into these muscles.
There are five different forms of CMT, and each is broken down in various subtypes depending on the gene responsible. CMT type 2D, which is caused by mutations in the GARS gene, is inherited in an autosomal dominant manner—this means that a person needs to inherit only one faulty copy of the GARS gene from one parent to get the disease.
The GARS gene holds the instructions for producing an enzyme called glycyl-tRNA synthase (GlyRS), which is vital to the process by which amino acids, the building blocks of proteins, are attached to one another during protein synthesis. So far, scientists have found 11 different kinds of mutations in the GARS gene that cause CMT type 2D. Some of the mutations affect the protein-building function of the GlyRS enzyme, but others don't, suggesting that a change in enzyme activity is not what causes CMT.
Thus, scientists have been trying to find a common feature shared by all GlyRS mutants that might explain the disease mechanism.
Structures in Solution
To find this common feature, Yang and colleagues turned to the three-dimensional structure of GlyRS. In 2007, they published the X-ray crystal structure of the wild-type protein and one of the mutants, but the structures were not all that different from each other (PNAS 104:11239-44, 2007).
"When we compared the wild type with the mutant, we did not find dramatic conformational change," said Weiwei He, a Scripps Research graduate student who joined Yang's lab and took on the project around the time of the 2007 paper's publication. "We thought maybe it was because of the crystal packing."
X-ray crystallography requires obtaining high amounts of a protein and packing the protein molecules into crystals that are bombarded with X-rays to determine the positions of all the atoms. This preparation, Yang and He reasoned, may mask any subtle conformation changes in a protein. "That is why we thought to look at the structure in solution, under more physiological conditions," said He.
In collaboration with Hui-Min Zhang, a postdoctoral fellow in the laboratory of Alan Marshall at the National High Magnetic Field Laboratory at Florida State University, Yang and He used a method to obtain the structures of five different GlyRS mutants and the wild-type protein in solution. This method, called hydrogen–deuterium exchange, gives information about which parts of a protein are in touch with a solution—in other words, which parts lie on the outside rather than being buried deep inside its three-dimensional shape. In collaboration with Min Guo, assistant professor at Scripps Florida, a second method, called small angle X-ray scattering, was used to measure changes in the overall shape of the protein structure in solution.
Together, the results revealed that every GARS mutation studied causes a structural opening in the resulting mutant protein. By superimposing the information obtained from the structures in solution to the high-resolution X-ray crystal structure of the wild-type GlyRS protein, Yang, He, Zhang and colleagues were able to determine that the structural opening maps to a common region of the GlyRS protein in all the mutants.
By becoming more open to potential new partners, the GlyRS mutants may gain a new function that is toxic to nerve cells. That would explain why CMT type 2D is inherited in a dominant fashion.
The team is now looking for proteins that might bind to this region and already have leads on several candidates. As exciting as this work is, says He, "this paper is just the start of the story; we have more story coming, and it's getting more and more exciting."
This disease mechanism may also apply to other conditions. "Some proteins may be relatively unstable and can be easily triggered into another conformation by different types of mutations," explained Yang. "This example deals with the GlyRS protein, but the general idea can be applied to many other mutation-induced human diseases."
One example may be ALS. Some inherited forms of ALS are caused in a gene that encodes the enzyme copper-zinc superoxide dismutase (commonly called SOD1). To date, more than 100 different mutations in the SOD1 gene have been linked to inherited ALS.
In addition to He, Zhang, Guo, Marshall, and Yang, Yeeting E. Chong of Scripps Research is a co-author of the paper, "Dispersed disease-causing neomorphic mutations on a single protein promote the same localized conformational opening."
The work was supported by grants from the National Institutes of Health, the National Science Foundation, and the State of Florida.
About The Scripps Research Institute
The Scripps Research Institute is one of the world's largest independent, non-profit biomedical research organizations. Scripps Research is internationally recognized for its discoveries in immunology, molecular and cellular biology, chemistry, neuroscience, and vaccine development, as well as for its insights into autoimmune, cardiovascular, and infectious disease. Headquartered in La Jolla, California, the institute also includes a campus in Jupiter, Florida, where scientists focus on drug discovery and technology development in addition to basic biomedical science. Scripps Research currently employs about 3,000 scientists, staff, postdoctoral fellows, and graduate students on its two campuses. The institute's graduate program, which awards Ph.D. degrees in biology and chemistry, is ranked among the top ten such programs in the nation. For more information, see www.scripps.edu .
Mika Ono | EurekAlert!
Hot cars can hit deadly temperatures in as little as one hour
24.05.2018 | Arizona State University
3D images of cancer cells in the body: Medical physicists from Halle present new method
16.05.2018 | Martin-Luther-Universität Halle-Wittenberg
The more electronics steer, accelerate and brake cars, the more important it is to protect them against cyber-attacks. That is why 15 partners from industry and academia will work together over the next three years on new approaches to IT security in self-driving cars. The joint project goes by the name Security For Connected, Autonomous Cars (SecForCARs) and has funding of €7.2 million from the German Federal Ministry of Education and Research. Infineon is leading the project.
Vehicles already offer diverse communication interfaces and more and more automated functions, such as distance and lane-keeping assist systems. At the same...
A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.
The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
25.05.2018 | Event News
02.05.2018 | Event News
13.04.2018 | Event News
25.05.2018 | Event News
25.05.2018 | Machine Engineering
25.05.2018 | Life Sciences