2023 July
Cryo-EM Scores Again
Posted on by Lawrence Tabak, D.D.S., Ph.D.
Human neurons are long, spindly structures, but if you could zoom in on their surfaces at super-high resolution, you’d see surprisingly large pores. They act as gated channels that open and close for ions and other essential molecules of life to pass in and out the cell. This rapid exchange of ions and other molecules is how neurons communicate, and why we humans can sense, think, move, and respond to the world around us [1].
Because these gated channels are so essential to neurons, mapping their precise physical structures at high-resolution has profound implications for informing future studies on the brain and nervous system. Good for us in these high-tech times that structural biologists keep getting better at imaging these 3D pores.
In fact, as just published in the journal Nature Communications [2], a team of NIH-supported scientists imaged the molecular structure of a gated pore of major research interest. The pore is called calcium homeostasis modulator 1 (CALHM1). Pictured below, you can view its 3D structure at near atomic resolution [2]. Keep in mind, this relatively large neuronal pore still measures approximately 50,000 times smaller than the width of a hair.
The structure comes from a research team led by Hiro Furukawa, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY. He and his team relied on cryo-electron microscopy (cryo-EM) to produce the first highly precise 3D models of CALHM1.
Cryo-EM involves flash-freezing molecules in liquid ethane and bombarding them with electrons to capture their images with a special camera. When all goes well, cryo-EM can reveal the structure of intricate macromolecular complexes in a matter of weeks.
Furukawa’s team had earlier studied CALHM1 from chickens with cryo-EM [3], and their latest work reveals that the human version is quite similar. Eight copies of the CALHM1 protein assemble to form the circular channel. Each of the protein subunits has a flexible arm that allows it to reach into the central opening, which the researchers now suspect allows the channels to open and close in a highly controlled manner. The researchers have likened the channels’ eight flexible arms to the arms of an octopus.
The researchers also found that fatty molecules called phospholipids play a critical role in stabilizing and regulating the eight-part channel. They used simulations to demonstrate how pockets in the CALHM1 channel binds this phospholipid over cholesterol to shore up the structure and function properly. Interestingly, these phospholipid molecules are abundant in many healthy foods, such as eggs, lean meats, and seafood.
Researchers knew that an inorganic chemical called ruthenium red can block the function of the CALHM1 channel. They’ve now shown precisely how this works. The structural details indicate that ruthenium red physically lodges in and plugs up the channel.
These details also may be useful in future efforts to develop drugs designed to target and modify the function of these channels in helpful ways. For instance, on our tongues, the channel plays a role in our ability to perceive sweet, sour, or umami (savory) flavors. In our brains, studies show the abnormal function of CALHM1 may be implicated in the plaques that accumulate in the brains of people with Alzheimer’s disease.
There are far too many other normal and abnormal functions to mention here in this brief post. Suffice it to say, I’ll look forward to seeing what this enabling research yields in the years ahead.
References:
[1] On the molecular nature of large-pore channels. Syrjanen, J., Michalski, K., Kawate, T., and Furukawa, H. J Mol Biol. 2021 Aug 20;433(17):166994. DOI: 10.1016/j.jmb.2021.166994. Epub 2021 Apr 16. PMID: 33865869; PMCID: PMC8409005.
[2] Structure of human CALHM1 reveals key locations for channel regulation and blockade by ruthenium red. Syrjänen JL, Epstein M, Gómez R, Furukawa H. Nat Commun. 2023 Jun 28;14(1):3821. DOI: 10.1038/s41467-023-39388-3. PMID: 37380652; PMCID: PMC10307800.
[3] Structure and assembly of calcium homeostasis modulator proteins. Syrjanen JL, Michalski K, Chou TH, Grant T, Rao S, Simorowski N, Tucker SJ, Grigorieff N, Furukawa H. Nat Struct Mol Biol. 2020 Feb;27(2):150-159. DOI: 10.1038/s41594-019-0369-9. Epub 2020 Jan 27. PMID: 31988524; PMCID: PMC7015811.
Links:
Brain Basics: The Life and Death of a Neuron (National Institute of Neurological Disorders and Stroke/NIH)
Alzheimer’s Disease (National Institute on Aging/NIH)
Furukawa Lab (Cold Spring Harbor Lab, Cold Spring Harbor, NY)
NIH Support: National Institute of Neurological Disorders and Stroke; National Institute of Mental Health
Understanding Causes of Devastating Neurodegenerative Condition Affecting Children
Posted on by Lawrence Tabak, D.D.S., Ph.D.
A common theme among parents and family members caring for a child with the rare Batten disease is “love, hope, cure.” While inspiring levels of love and hope are found among these amazing families, a cure has been more elusive. One reason is rooted in the need for more basic research. Although researchers have identified an altered gene underlying Batten disease, they’ve had difficulty pinpointing where and how the gene’s abnormal protein product malfunctions, especially in cells within the nervous system.
Now, this investment in more basic research has paid off. In a paper just published in the journal Nature Communications, an international research team pinpointed where and how a key cellular process breaks down in the nervous system to cause Batten disease, sometimes referred to as CLN3 disease [1]. While there’s still a long way to go in learning exactly how to overcome the cellular malfunction, the findings mark an important step forward toward developing targeted treatments for Batten disease and progress in the quest for a cure.
The research also offers yet another excellent example of how studying rare diseases helps to advance our fundamental understanding of human biology. It shows that helping those touched by Batten disease can shed a brighter light on basic cellular processes that drive other diseases, rare and common.
Batten disease affects about 14,000 people worldwide [2]. For those with the juvenile form of this inherited disease of the nervous system, parents may first notice their seemingly healthy child has difficulty saying words, sudden problems with vision or movement, and changes in behavior. Tragically for parents, with no approved treatments to reverse these symptoms, the disease will worsen, leading to severe vision loss, frequent seizures, and impaired motor skills. The disease can be fatal as early as late childhood or the teenage years.
Batten disease also goes by the more technical name of juvenile neuronal ceroid lipofuscinosis. Using this technical name, it represents one of the more than 70 medically recognized lysosomal storage disorders.
These disorders share a breakdown in the ability of membrane-bound cellular components, known as lysosomes, to degrade the molecular waste products of normal cell biology. As a result, all this undegraded material builds up and eventually kills affected cells. In people with Batten disease, the lost and damaged cells cause progressive dysfunction within the nervous system.
Researchers have known for a while that the most common cause of this breakdown in people with Batten disease is the inheritance of two defective copies of a gene called CLN3. As mentioned above, what’s been missing is a more detailed understanding of what exactly a working copy of the CLN3 gene does and how its loss leads to the changes seen in those with this condition.
Hoping to solve this puzzle was an NIH-supported basic research team led by Alessia Calcagni and Andrea Ballabio, Baylor College of Medicine and Texas Children’s Hospital, Houston, and Telethon Institute of Genetics and Medicine, Naples, Italy.
As described in their latest paper, the researchers first generated an antibody that allowed them to visualize where in cells the protein encoded by CLN3 is found. Their studies unexpectedly showed that this protein has a role outside, not inside, the cell’s estimated 50-to-1,000 lysosomes. Before reaching the lysosomes, the protein first moves through another cellular component called the Golgi body, where many proteins are packaged.
They then identified all the other proteins that interact with the CLN3 protein in the Golgi body and elsewhere in the cell. Their data showed that CLN3 interacts with proteins known for transporting other proteins within the cell and forming new lysosomes.
That gave them a valuable clue: the CLN3 gene must be a player in these fundamentally important cellular processes of protein transport and lysosome formation. Among the proteins CLN3 interacts with in the Golgi body is a particular receptor called M6PR. The receptor known for its role in recognizing lysosomal enzymes and delivering them to the lysosomes, where they go to work inside these bubble-like structures degrading cellular waste products.
The researchers found that loss of CLN3 led this important M6PR receptor to be broken down within lysosomes. The breakdown, in turn, altered the normal shape of new lysosomes, and that limits their functionality. The researchers also showed that restoring CLN3 in cells that lacked this gene also restored the production of more functional lysosomes and lysosomal enzymes.
Overall, the findings point to a major role for CLN3 in the formation of lysosomes and their ability to function. Importantly, the findings also offer clues for understanding the mechanisms that underlie other forms of lysosomal storage disease, which collectively affect as many as one in every 40,000 people [3]. The work also may have broader implications for common neurodegenerative diseases, such as Parkinson’s and Alzheimer’s disease.
Most of all, this paper demonstrates the power of basic research to define needed molecular targets. It shows how these fundamental studies are helping families affected by Batten disease and supporting their love, hope, and quest for a cure.
References:
[1] Loss of the batten disease protein CLN3 leads to mis-trafficking of M6PR and defective autophagic-lysosomal reformation. Calcagni’ A, Staiano L, Zampelli N, Minopoli N, Herz NJ, Cullen PJ, Parenti G, De Matteis MA, Grumati P, Ballabio A, et al. Nat Commun. 2023 Jul 3;14(1):3911. doi: 10.1038/s41467-023-39643-7. PMID: 37400440; PMCID: PMC10317969.
[2] Batten Disease. Boston Children’s Hospital.
[3] Lysosomal storage diseases. Cleveland Clinic fact sheet, June 27, 2022.
Links:
Batten Disease (National Institute of Neurological Disorders and Stroke/NIH)
Rare Diseases (NIH)
Alessia Calcagni (Baylor College of Medicine, Houston, TX)
Andrea Ballabio (Telethon Institute of Genetics and Medicine, Naples, Italy)
NIH Support: National Institute of Neurological Disorders and Stroke; National Cancer Institute; National Center for Advancing Translational Sciences
Visit the New NIH Virtual Tour
Posted on by Lawrence Tabak, D.D.S., Ph.D.
Happy Fourth of July! Before everyone heads out to celebrate the holiday with their family and friends, I want to share this brief video with you. It’s an introduction to the brand-new NIH Virtual Tour that’s now available on our website. When time permits, I encourage everyone to take the full tour of our Bethesda, MD, main campus and explore this great institution of science, technological innovation, and, above all, hope.
Among the virtual tour’s many features is an interactive, aerial map of the 32 buildings on our Bethesda campus. By clicking on a highlighted building, you can explore an impressive multimedia gallery of photos, video clips, and other resources. The tour will allow you to learn more about NIH and the ways in which we help people live longer and healthier lives.
You also can learn more about NIH’s 27 Institutes and Centers, including the NIH Clinical Center and 20 other in-depth tour stops—from research labs to patient rooms—and hear directly from some of our impressive researchers, leaders, and patients. For example, you can learn about chronic pain research from a lab in the NIH Clinical Center or see the largest zebrafish facility in the world, housed in Building 6.
What I like most about the virtual tour is that it captures what makes NIH so special—the many amazing people who collaborate every day to discover ways to solve seemingly intractable research problems. I admire their commitment to follow the science wherever it may lead.
In fact, from its humble beginnings in a one-room laboratory in 1887, NIH has become the world’s largest funder of medical research, whether that’s mobilizing to combat a deadly pandemic or strategizing to help people with a rare disorder find answers.
Not only does NIH conduct groundbreaking research in its own labs and clinics, it also supports much of the medical research conducted at universities and institutions in your states and local communities. Whether in Bethesda or beyond the Beltway, this national research effort will continue to yield the needed understanding to turn discovery into better health, helping more people to flourish and lead fully productive lives, now and in the generations to come.
That’s certainly something we can all celebrate this holiday, the 247th birthday of our great nation that I’m so honored to serve. Have a great, but safe, Fourth of July, and I’ll see you back here soon to share another blog post and another story of NIH-supported research progress.
Links:
Virtual Tour (NIH)
Visitor Information (NIH)
