Each time your cells divide, telomeres—complexes of specialized DNA sequences, RNA, and protein that protect the tips of your chromosomes—shorten just a bit. And, as the video shows, that shortening renders the genomic information on your chromosomes more vulnerable to changes that can drive cancer and other diseases of aging.
Consequently, over the last few decades, much research has focused on efforts to understand telomerase, a naturally occurring enzyme that helps to replace the bits of telomere lost during cell division. But there’s been a major hitch: until recently, scientists hadn’t been able to determine telomerase’s molecular structure in detail—a key step in figuring out exactly how the enzyme works. Now, thanks to better purification methods and an exciting technology called cryo-electron microscopy (cryo-EM), NIH-funded researchers and their colleagues have risen to the challenge to produce the most detailed view yet of human telomerase in its active form .
This structural biology advance is a critical step toward learning more about the role of telomerase in cancers, as well as genetic conditions linked to telomerase deficiencies. It’s also an important milestone in the quest for drugs targeting telomerase in different ways, perhaps to slow the growth of cancerous cells or to boost the proliferative capacity of life-giving adult stem cells.
One reason telomerase has been so difficult to study in humans is that the enzyme isn’t produced at detectable levels in the vast majority of our cells. To get around this problem, the team led by Eva Nogales and Kathleen Collins at the University of California, Berkeley, first coaxed human cells in the lab to produce larger quantities of active telomerase. They then used fluorescent microscopy, along with extensive knowledge of the enzyme’s biochemistry, to develop a multi-step purification process that yielded relatively homogenous samples of active telomerase.
The new study is also yet another remarkable example of how cryo-EM microscopy has opened up new realms of scientific possibility. That’s because, in comparison to other methods, cryo-EM enables researchers to solve complex macromolecular structures even when only tiny amounts of material are available. It can also produce detailed images of molecules, like telomerase, that are extremely flexible and hard to keep still while taking a picture of their structure.
As described in Nature, the researchers used cryo-EM to capture the structure of human telomerase in unprecedented detail. Their images reveal two lobes, held together by a flexible RNA tether. One of those lobes contains the highly specialized core enzyme. It uses an internal RNA template as a guide to make the repetitive, telomeric DNA that’s added at the tips of chromosomes. The second lobe, consisting of a complex of RNA and RNA-binding proteins, plays important roles in keeping the complex stable and properly in place.
This new, more-detailed view helps to explain how mutations in particular genes may lead to telomerase-related health conditions, including bone marrow failure, as well as certain forms of anemia and pulmonary fibrosis. For example, it reveals that a genetic defect known to cause bone marrow failure affects an essential protein in a spot that’s especially critical for telomerase’s proper conformation and function.
This advance will also be a big help for designing therapies that encourage telomerase activity. For example, it could help to boost the success of bone marrow transplants by rejuvenating adult stem cells. It might also be possible to reinforce the immune systems of people with HIV infections. While telomerase-targeted treatments surely won’t stop people from growing old, new insights into this important enzyme will help to understand aging better, including why some people appear to age faster than others.
As remarkable as these new images are, the researchers aren’t yet satisfied. They’ll continue to refine them down to the minutest structural details. They say they’d also like to use cryo-EM to understand better how the complex attaches to chromosomes to extend telomeres. Each new advance in the level of atomic detail will not only make for amazing new videos, it will help to advance understanding of human biology in health, aging, and disease.
 Cryo-EM structure of substrate-bound human telomerase holoenzyme. Nguyen THD, Tam J, Wu RA, Greber BJ, Toso D, Nogales E, Collins K. Nature. 2018 April 25. [Epub ahead of publication]
High Resolution Electron Microscopy (National Cancer Institute/NIH)
Nogales Lab (University of California, Berkeley)
Collins Lab (University of California, Berkeley)
NIH Support: National Institute of General Medical Sciences
Tags: aging, anemia, biochemistry, bone marrow transplant, cancer, cell division, chromosome, Cool Videos, cryo-EM, DNA, drug design, holoenzyme, imaging, immunity, microscopy, structural biology, telomerase, telomeres
I want to wish everyone a Happy New Year! Hope your 2018 is off to a great start.
Over the holidays, the journal Science published its annual, end-of-the-year list of research breakthroughs, from anthropology to zoology. I always look forward to seeing the list and reflecting on some of the stunning advances reported in the past 12 months. Last year was no exception. Science’s 2017 Breakthrough of the Year, as chosen by its editors, was in the field of astrophysics. Scientists were able to witness the effects of the collision of two neutron stars—large stars with collapsed inner cores—smacking into each other 130 million light years away. How cool is that!
Numbered prominently among the nine other breakthroughs were five from biomedicine: gene therapy, gene editing, cancer immunotherapy, cryo-EM, and biology preprints. All involved varying degrees of NIH support, and all drew great interest from readers. In fact, three of the top four vote-getters in the “People’s Choice” category came from biomedicine. That includes the People’s 2017 Breakthrough of the Year: gene therapy success. And so, in what has become a Director’s Blog tradition, I’ll kick off our new year of posts by taking a closer look at these biomedical breakthroughs—starting with the little girl in the collage above, and moving clockwise around the images:
Tags: 2017 Nobel Prize in Chemistry, ALL, axicabtagene ciloleucel, B-cell acute lymphoblastic leukemia, cancer, cancer immunotherapy, car t-cell therapy, CRISPR/Cas9, cryo-electron microscopy, cryo-EM, gene editing, gene therapy, Huntington's disease, immunotherapy, inherited retinal degenerations, Kymriah, mismatch repair, nusineren, pembrolizumab, preprints, RNA editing, Science’s 2017 Breakthrough of the Year, sickle cell disease, spinraza, tisagenlecleucel, wearable devices, Yescarta
The stars are out and shining this holiday season. But there are some star-shaped structures now under study in the lab that also give us plenty of reason for hope. One of them is a tiny virus called bacteriophage phi-6, which researchers are studying in an effort to combat a similar, but more-complex, group of viruses that can cause life-threatening dehydration in young children.
Thanks to a breakthrough technology called cryo-electron microscopy (cryo-EM), NIH researchers recently captured, at near atomic-level of detail, the 3D structure of this immature bacteriophage phi-6 particle in the process of replication. At the points of its “star,” key proteins (red) are positioned to transport clipped, single-stranded segments of the virus’ own genetic information into its newly made shell, or procapsid (blue). Once inside the procapsid, an enzyme (purple) will copy the segments to make the genetic information double-stranded, while another protein (yellow) will help package them. As the procapsid matures, it undergoes dramatic structural changes.
Tags: bacteriophage, bacteriophage phi-6, cryo-electron microscopy, cryo-EM, double-stranded RNA viruses, gastrointestinal disease, global health, imaging, procapsid, rotavirus, rotavirus vaccine, virus
When Dmitry Lyumkis headed off to graduate school at The Scripps Research Institute, La Jolla, CA, he had thoughts of becoming a synthetic chemist. But he soon found his calling in a nearby lab that imaged proteins using a technique known as single-particle cryo-electron microscopy (EM). Lyumkis was amazed that the team could take a purified protein, flash-freeze it in liquid nitrogen, and then fire electrons at the protein, capturing the resulting image with a special camera. Also amazing was the sophisticated computer software that analyzed the raw 2D camera images, merging the data and reconstructing it into 3D representations of the protein.
The work was profoundly complex, but Lyumkis thrives on solving extremely difficult puzzles. He joined the Scripps lab to become a structural biologist and a few years later used single-particle cryo-EM to help determine the atomic structure of a key protein on the surface of the human immunodeficiency virus (HIV), the cause of AIDS. The protein had been considered one of the greatest challenges in structural biology and a critical target in developing an AIDS vaccine .
Now, Lyumkis has plans to take single-particle cryo-EM to a whole new level—literally. He wants to develop new methods that allow it to model the atomic structures of much smaller proteins. Right now, single-particle cryo-EM has worked with proteins as small as roughly 150 kilodaltons, a measure of a protein’s molecular weight (the approximate average mass of a protein is 53 kDa). Lyumkis plans to drop that number well below 100 kDa, noting that if his new methods work as he hopes, there should be very little, if any, lower size limit to get the technique to work. He envisions generating within a matter of days or weeks the precise structure of an average-sized protein involved in a disease, and then potentially handing it off as an atomic model for drug developers to target for more effective treatment.
Tags: 2015 NIH Director’s Early Independence Award, 3D computational analysis, atomic structure, computation, cryo-electron microscopy, cryo-EM, drug design, drug discovery, drugs, electron microscopy, HIV, human immunodeficiency virus, IKK complex, protein structure, proteins, single-particle cryo-EM, small proteins, structural biology