NIH researchers develop three-dimensional structure of twinkle protein

Researchers at the National Institutes of Health have developed a three-dimensional structure that allows them to see how and where disease mutations on the twinkle protein can lead to mitochondrial disease. The protein is involved in helping cells use energy that our bodies convert from food. Prior to the development of this 3D structure, researchers only had models and could not determine how these mutations contribute to disease. Mitochondrial diseases are a group of inherited disorders that affect 1 in 5,000 people and require very few treatments.

For the first time, we can map the mutations that cause some of these devastating diseases. Clinicians can now see where these mutations lie and use this information to identify causes and help families make choices, including decisions about having more children.”

Amanda A. Riccio, Ph.D., lead author, researcher in the Mitochondrial DNA Replication Group at the National Institute of Environmental Health Sciences (NIEHS)

The new findings will be particularly relevant for developing targeted treatments for patients suffering from mitochondrial diseases such as progressive external ophthalmoplegia, a condition that can lead to loss of muscle functions involved in eye and eyelid movements; Perrault syndrome, a rare genetic disorder that can cause hearing loss; infantile spinocerebellar ataxia, an inherited neurological disorder; and hepatocerebral mitochondrial DNA (mtDNA) depletion syndrome, an inherited disease that can lead to liver failure and neurological complications during childhood.

The paper appearing in the Proceedings of the National Academy of Sciences shows how the NIEHS researchers were the first to accurately map clinically relevant variants in the twinkle helicase, the enzyme that unwinds the mitochondrial DNA double helix. The twinkle structure and all coordinates are now available in the open data Protein Data Bank that is freely available to all researchers.

“Twinkle’s structure has eluded researchers for years. It’s a very difficult protein to work with,” noted William C. Copeland, Ph.D., who leads the Mitochondrial DNA Replication Group and is the corresponding author on the paper. . “By stabilizing the protein and using the best equipment in the world, we were able to build the last missing piece for the human mitochondrial DNA replisome.”

The researchers used cryoelectron microscopy (CryoEM), which allowed them to look inside the protein and the intricate structures of hundreds of amino acids or residues and how they interact.

Mitochondria, which are responsible for energy production, are particularly vulnerable to mutations. mtDNA mutations can interfere with their ability to efficiently generate energy for the cell. Unlike other specialized structures in cells, mitochondria have their own DNA. There are two copies of each chromosome in the nucleus, but in the mitochondria there can be thousands of copies of mtDNA. With a large number of mitochondrial chromosomes, the cell can tolerate a few mutations, but accumulation of too many mutated copies leads to mitochondrial disease.

To conduct the study, the researchers used a clinical mutation, W315L, known to cause progressive external ophthalmoplegia, to fix the structure. Using CryoEM, they were able to observe thousands of protein particles that appeared in different orientations. The final structure shows a circular arrangement with multiple proteins. They also used mass spectrometry to verify the structure and then did computer simulations to understand why the mutation leads to disease.

In no time, they were able to map up to 25 disease-causing mutations. They found that many of these disease mutations map right at the intersection of two protein subunits, suggesting that mutations in this region would weaken the interaction between the subunits and prevent the helicase from functioning.

“The arrangement of the twinkle is a lot like a puzzle. A clinical mutation can change the shape of the twinkle pieces and they may no longer fit together properly to perform their intended function,” explains Riccio.

“What’s so great about Dr. Riccio and the team’s work is that the structure allows you to see so many of these disease mutations gathered in one place,” said Matthew J. Longley, Ph.D., an author and NIEHS researcher. researcher. “It’s very unusual to see one paper explaining so many clinical mutations. Thanks to this work, we’re one step closer to having information that can be used to develop treatments for these debilitating diseases.”


National Health Institutes

Reference magazine:

Riccio, AA et al. (2022) Structural understanding and characterization of human Twinkle helicase in mitochondrial disease. PNAS.

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