cryo-electron microscopy
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
What A Year It Was for Science Advances!
Posted on by Dr. Francis Collins
At the close of every year, editors and writers at the journal Science review the progress that’s been made in all fields of science—from anthropology to zoology—to select the biggest advance of the past 12 months. In most cases, this Breakthrough of the Year is as tough to predict as the Oscar for Best Picture. Not in 2020. In a year filled with a multitude of challenges posed by the emergence of the deadly coronavirus disease 2019 (COVID-2019), the breakthrough was the development of the first vaccines to protect against this pandemic that’s already claimed the lives of more than 360,000 Americans.
In keeping with its annual tradition, Science also selected nine runner-up breakthroughs. This impressive list includes at least three areas that involved efforts supported by NIH: therapeutic applications of gene editing, basic research understanding HIV, and scientists speaking up for diversity. Here’s a quick rundown of all the pioneering advances in biomedical research, both NIH and non-NIH funded:
Shots of Hope. A lot of things happened in 2020 that were unprecedented. At the top of the list was the rapid development of COVID-19 vaccines. Public and private researchers accomplished in 10 months what normally takes about 8 years to produce two vaccines for public use, with more on the way in 2021. In my more than 25 years at NIH, I’ve never encountered such a willingness among researchers to set aside their other concerns and gather around the same table to get the job done fast, safely, and efficiently for the world.
It’s also pretty amazing that the first two conditionally approved vaccines from Pfizer and Moderna were found to be more than 90 percent effective at protecting people from infection with SARS-CoV-2, the coronavirus that causes COVID-19. Both are innovative messenger RNA (mRNA) vaccines, a new approach to vaccination.
For this type of vaccine, the centerpiece is a small, non-infectious snippet of mRNA that encodes the instructions to make the spike protein that crowns the outer surface of SARS-CoV-2. When the mRNA is injected into a shoulder muscle, cells there will follow the encoded instructions and temporarily make copies of this signature viral protein. As the immune system detects these copies, it spurs the production of antibodies and helps the body remember how to fend off SARS-CoV-2 should the real thing be encountered.
It also can’t be understated that both mRNA vaccines—one developed by Pfizer and the other by Moderna in conjunction with NIH’s National Institute of Allergy and Infectious Diseases—were rigorously evaluated in clinical trials. Detailed data were posted online and discussed in all-day meetings of an FDA Advisory Committee, open to the public. In fact, given the high stakes, the level of review probably was more scientifically rigorous than ever.
First CRISPR Cures: One of the most promising areas of research now underway involves gene editing. These tools, still relatively new, hold the potential to fix gene misspellings—and potentially cure—a wide range of genetic diseases that were once to be out of reach. Much of the research focus has centered on CRISPR/Cas9. This highly precise gene-editing system relies on guide RNA molecules to direct a scissor-like Cas9 enzyme to just the right spot in the genome to cut out or correct a disease-causing misspelling.
In late 2020, a team of researchers in the United States and Europe succeeded for the first time in using CRISPR to treat 10 people with sickle cell disease and transfusion-dependent beta thalassemia. As published in the New England Journal of Medicine, several months after this non-heritable treatment, all patients no longer needed frequent blood transfusions and are living pain free [1].
The researchers tested a one-time treatment in which they removed bone marrow from each patient, modified the blood-forming hematopoietic stem cells outside the body using CRISPR, and then reinfused them into the body. To prepare for receiving the corrected cells, patients were given toxic bone marrow ablation therapy, in order to make room for the corrected cells. The result: the modified stem cells were reprogrammed to switch back to making ample amounts of a healthy form of hemoglobin that their bodies produced in the womb. While the treatment is still risky, complex, and prohibitively expensive, this work is an impressive start for more breakthroughs to come using gene editing technologies. NIH, including its Somatic Cell Genome Editing program, continues to push the technology to accelerate progress and make gene editing cures for many disorders simpler and less toxic.
Scientists Speak Up for Diversity: The year 2020 will be remembered not only for COVID-19, but also for the very public and inescapable evidence of the persistence of racial discrimination in the United States. Triggered by the killing of George Floyd and other similar events, Americans were forced to come to grips with the fact that our society does not provide equal opportunity and justice for all. And that applies to the scientific community as well.
Science thrives in safe, diverse, and inclusive research environments. It suffers when racism and bigotry find a home to stifle diversity—and community for all—in the sciences. For the nation’s leading science institutions, there is a place and a calling to encourage diversity in the scientific workplace and provide the resources to let it flourish to everyone’s benefit.
For those of us at NIH, last year’s peaceful protests and hashtags were noticed and taken to heart. That’s one of the many reasons why we will continue to strengthen our commitment to building a culturally diverse, inclusive workplace. For example, we have established the NIH Equity Committee. It allows for the systematic tracking and evaluation of diversity and inclusion metrics for the intramural research program for each NIH institute and center. There is also the recently founded Distinguished Scholars Program, which aims to increase the diversity of tenure track investigators at NIH. Recently, NIH also announced that it will provide support to institutions to recruit diverse groups or “cohorts” of early-stage research faculty and prepare them to thrive as NIH-funded researchers.
AI Disentangles Protein Folding: Proteins, which are the workhorses of the cell, are made up of long, interconnected strings of amino acids that fold into a wide variety of 3D shapes. Understanding the precise shape of a protein facilitates efforts to figure out its function, its potential role in a disease, and even how to target it with therapies. To gain such understanding, researchers often try to predict a protein’s precise 3D chemical structure using basic principles of physics—including quantum mechanics. But while nature does this in real time zillions of times a day, computational approaches have not been able to do this—until now.
Of the roughly 170,000 proteins mapped so far, most have had their structures deciphered using powerful imaging techniques such as x-ray crystallography and cryo–electron microscopy (cryo-EM). But researchers estimate that there are at least 200 million proteins in nature, and, as amazing as these imaging techniques are, they are laborious, and it can take many months or years to solve 3D structure of a single protein. So, a breakthrough certainly was needed!
In 2020, researchers with the company Deep Mind, London, developed an artificial intelligence (AI) program that rapidly predicts most protein structures as accurately as x-ray crystallography and cryo-EM can map them [2]. The AI program, called AlphaFold, predicts a protein’s structure by computationally modeling the amino acid interactions that govern its 3D shape.
Getting there wasn’t easy. While a complete de novo calculation of protein structure still seemed out of reach, investigators reasoned that they could kick start the modeling if known structures were provided as a training set to the AI program. Utilizing a computer network built around 128 machine learning processors, the AlphaFold system was created by first focusing on the 170,000 proteins with known structures in a reiterative process called deep learning. The process, which is inspired by the way neural networks in the human brain process information, enables computers to look for patterns in large collections of data. In this case, AlphaFold learned to predict the underlying physical structure of a protein within a matter of days. This breakthrough has the potential to accelerate the fields of structural biology and protein research, fueling progress throughout the sciences.
How Elite Controllers Keep HIV at Bay: The term “elite controller” might make some people think of video game whizzes. But here, it refers to the less than 1 percent of people living with human immunodeficiency virus (HIV) who’ve somehow stayed healthy for years without taking antiretroviral drugs. In 2020, a team of NIH-supported researchers figured out why this is so.
In a study of 64 elite controllers, published in the journal Nature, the team discovered a link between their good health and where the virus has inserted itself in their genomes [3]. When a cell transcribes a gene where HIV has settled, this so-called “provirus,” can produce more virus to infect other cells. But if it settles in a part of a chromosome that rarely gets transcribed, sometimes called a gene desert, the provirus is stuck with no way to replicate. Although this discovery won’t cure HIV/AIDS, it points to a new direction for developing better treatment strategies.
In closing, 2020 presented more than its share of personal and social challenges. Among those challenges was a flood of misinformation about COVID-19 that confused and divided many communities and even families. That’s why the editors and writers at Science singled out “a second pandemic of misinformation” as its Breakdown of the Year. This divisiveness should concern all of us greatly, as COVID-19 cases continue to soar around the country and our healthcare gets stretched to the breaking point. I hope and pray that we will all find a way to come together, both in science and in society, as we move forward in 2021.
References:
[1] CRISPR-Cas9 gene editing for sickle cell disease and β-thalassemia. Frangoul H et al. N Engl J Med. 2020 Dec 5.
[2] ‘The game has changed.’ AI triumphs at protein folding. Service RF. Science. 04 Dec 2020.
[3] Distinct viral reservoirs in individuals with spontaneous control of HIV-1. Jiang C et al. Nature. 2020 Sep;585(7824):261-267.
Links:
COVID-19 Research (NIH)
2020 Science Breakthrough of the Year (American Association for the Advancement of Science, Washington, D.C)
Caught on Camera: Neutralizing Antibodies Interacting with SARS-CoV-2
Posted on by Dr. Francis Collins
As this long year enters its final month, there is good reason to look ahead to 2021 with optimism that the COVID-19 pandemic will finally be contained. The Food and Drug Administration is now reviewing the clinical trial data of the Pfizer and Moderna vaccines to ensure their safety and efficacy. If all goes well, emergency use authorization could come very soon, allowing immunizations to begin.
Work also continues on developing better therapeutics against SARS-CoV-2, the novel coronavirus that causes COVID-19. Though we’ve learned a great deal about this coronavirus in a short time, structural biologists continue to produce more detailed images that reveal more precisely where and how to target SARS-CoV-2. This research often involves neutralizing antibodies that circulate in the blood of most people who’ve recovered from COVID-19. The study of such antibodies and how they interact with SARS-CoV-2 offers critical biological clues into how to treat and prevent COVID-19.
A recent study in the journal Nature brings more progress, providing the most in-depth analysis yet of how human neutralizing antibodies physically grip SARS-CoV-2 to block it from binding to our cells [1]. To conduct this analysis, a team of NIH-supported structural biologists, led by postdoc Christopher Barnes and Pamela Björkman, California Institute of Technology, Pasadena, used the power of cryo-electron microscopy (cryo-EM) to capture complex molecular interactions at near-atomic scale.
People infected with SARS-CoV-2 (or any foreign substance, for that matter) generate thousands of different versions of attack antibodies. Some of these antibodies are very good at sticking to the coronavirus, while others attach only loosely. Barnes used cryo-EM to capture highly intricate pictures of eight different human neutralizing antibodies bound tightly to SARS-CoV-2. Each of these antibodies, which had been isolated from patients a few weeks after they developed symptoms of COVID-19, had been shown in lab tests to be highly effective at blocking infection.
The researchers mapped all physical interactions between several human neutralizing antibodies and SARS-CoV-2’s spike protein that stud its surface. The virus uses these spiky extensions to infect a human cell by grabbing on to the angiotensin-converting enzyme 2 (ACE2) receptor. The molecular encounter between the coronavirus and ACE2 takes place via one or more of a trio of three protein domains, called receptor-binding domains (RBDs), that jut out from its spikes. RBDs flap up and down in the fluid surrounding cells, “reaching up” to touch and enter, or “laying down” to hide from an infected person’s antibodies and immune cells. Only an “up” RBD can attach to ACE2 and get into a cell.
Taken together with other structural information known about SARS-CoV-2, Barnes’ cryo-EM snapshots revealed four different types of shapes, or classes, of antibody-spike combinations. These high-resolution molecular views show that human neutralizing antibodies interact in many different ways with SARS-CoV-2: blocking access to either one or more RBDs in their “up” or “down” positions.
These results tell us a number of things, including underscoring why strategies that combine multiple types of antibodies in an “antibody cocktail” might likely offer broader protection against infection than using just a single type of antibody. Indeed, that approach is currently being tested in patients with COVID-19.
The findings also provide a molecular guide for custom-designing synthetic antibodies in the lab to foil SARS-CoV-2. As one example, Barnes and his team observed that one antibody completely locked all three RBDs into closed (“down”) positions. As you might imagine, scientists might want to copy that antibody type when designing an antibody-based drug or vaccine.
It is tragic that hundreds of thousands of people have died from this terrible new disease. Yet the immune system helps most to recover. Learning as much as we possibly can from those individuals who’ve been infected and returned to health should help us understand how to heal others who develop COVID-19, as well as inform precision design of additional vaccines that are molecularly targeted to this new foe.
While we look forward to the arrival of COVID-19 vaccines and their broad distribution in 2021, each of us needs to remember to practice the three W’s: Wear a mask. Watch your distance (stay 6 feet apart). Wash your hands often. In parallel with everyone adopting these critical public health measures, the scientific community is working harder than ever to meet this moment, doing everything possible to develop safe and effective ways of treating and preventing COVID-19.
Reference:
[1] SARS-CoV-2 neutralizing antibody structures inform therapeutic strategies. Barnes CO, Jette CA, Abernathy ME, et al. Nature. 2020 Oct 12. [Epub ahead of print].
Links:
Coronavirus (COVID-19) (NIH)
Combat COVID (U.S. Department of Health and Human Services, Washington, D.C.)
Freezing a Moment in Time: Snapshots of Cryo-EM Research (National Institute of General Medical Sciences/NIH)
Björkman Lab (California Institute of Technology, Pasadena)
NIH Support: National Institute of General Medical Sciences; National Institute of Allergy and Infectious Diseases
Pursuing Safe and Effective Anti-Viral Drugs for COVID-19
Posted on by Dr. Francis Collins
Right now, the world is utterly focused on the coronavirus outbreak known as COVID-19. That’s certainly true for those of us at NIH. Though I am working from home to adhere rigorously to physical distancing, I can’t remember ever working harder, trying to do everything I can to assist in the development of safe and effective treatments and vaccines.
Over the past several weeks, a mind-boggling array of possible therapies have been considered. None have yet been proven to be effective in rigorously controlled trials, but for one of them, it’s been a busy week. So let’s focus on an experimental anti-viral drug, called remdesivir, that was originally developed for the deadly Ebola virus. Though remdesivir failed to help people with Ebola virus disease, encouraging results from studies of coronavirus-infected animals have prompted the launch of human clinical trials to see if this drug might fight SARS-CoV-2, the novel coronavirus that causes COVID-19.
You may wonder how a drug could possibly work for Ebola and SARS-CoV-2, since they are very different viruses that produce dramatically different symptoms in humans. The commonality is that both viruses have genomes made of ribonucleic acid (RNA), which must be copied by an enzyme called RNA-dependent RNA polymerase for the virus to replicate.
Remdesivir has an affinity for attaching to this kind of polymerase because its structure is very similar to one of the RNA letters that make up the viral genome [1]. Due to this similarity, when an RNA virus attempts to replicate, its polymerase is tricked into incorporating remdesivir into its genome as a foreign nucleotide, or anomalous letter. That undecipherable, extra letter brings the replication process to a crashing halt—and, without the ability to replicate, viruses can’t infect human cells.
Would this work on a SARS-CoV-2 infection in a living organism? An important step was just posted as a preprint yesterday—a small study showed infusion of remdesivir was effective in limiting the severity of lung disease in rhesus macaques [2]. That’s encouraging news. But the only sure way to find out if remdesivir will actually help humans who are infected with SARS-CoV-2 is to conduct a randomized, controlled clinical trial.
In late February, NIH’s National Institute of Allergy and Infectious Diseases (NIAID) did just that, when it launched a randomized, controlled clinical trial to test remdesivir in people with COVID-19. The study, led by NIAID’s Division of Microbiology and Infectious Diseases, has already enrolled 805 patients at 67 testing sites. Most sites are in the United States, but there are also some in Singapore, Japan, South Korea, Mexico, Spain, the United Kingdom, Denmark, Greece, and Germany.
All trial participants must have laboratory-confirmed COVID-19 infections and evidence of lung involvement, such as abnormal chest X-rays, rattling sounds when breathing (rales) with a need for supplemental oxygen, or a need for mechanical ventilation. They are randomly assigned to receive either a round of treatment with remdesivir or a harmless placebo with no therapeutic effect. To avoid bias from creeping into patient care, the study is double-blind, meaning neither the medical staff nor the participants know who is receiving remdesivir.
There is also an early hint from another publication that remdesivir may benefit some people with COVID-19. Since the end of January 2020, Gilead Sciences, Foster City, CA, which makes remdesivir, has provided daily, intravenous infusions of the drug on a compassionate basis to more than 1,800 people hospitalized with advanced COVID-19 around the world. In a study of a subgroup of 53 compassionate-use patients with advanced complications of COVID-19, nearly two-thirds improved when given remdesivir for up to 10 days [3]. Most of the participants were men over age 60 with preexisting conditions that included hypertension, diabetes, high cholesterol, and asthma.
This may sound exciting, but these preliminary results, published in the New England Journal of Medicine, come with major caveats. There were no controls, participants were not randomized, and the study lacked other key features of the more rigorously designed NIH clinical trial. We can all look forward to the results from the NIH trial, which are are expected within a matter of weeks. Hopefully these will provide much-needed scientific evidence on remdesivir’s safety and efficacy in people with COVID-19.
In the meantime, basic researchers continue to learn more about remdesivir and its interaction with the novel coronavirus that causes COVID-19. In a recent study in the journal Science, a research team, led by Quan Wang, Shanghai Tech University, China, mapped the 3D atomic structure of the novel coronavirus’s polymerase while it was complexed with two other vital parts of the viral replication machinery [4]. This was accomplished using a high-resolution imaging approach called cryo-electron microscopy (cryo-EM), which involves flash-freezing molecules in liquid nitrogen and bombarding them with electrons to capture their images with a special camera.
With these atomic structures in hand, the researchers then modeled exactly how remdesivir binds to the polymerase of the novel coronavirus. The model will help inform future efforts to tweak the structure of the drug and optimize its ability to disrupt viral replication. Such detailed biochemical information will be vital in the weeks ahead, especially if data generated by the NIH clinical trial indicate that remdesivir is a worthwhile lead to pursue in our ongoing search for anti-viral drugs to combat the global COVID-19 pandemic.
References:
[1] Nucleoside analogues for the treatment of coronavirus infections. Pruijssers AJ, Denison MR. Curr Opin Virol. 2019 Apr;35:57-62.
[2] Clinical benefit of remdesivir in rhesus macaques infected with SARS-CoV-2. Williamson B, Feldmann F, Schwarz B, Scott D, Munster V, de Wit E et. al. BioRxiv. Preprint posted 15 April 2020.
[3] Compassionate use of remdesivir for patients with severe Covid-19. Grein J, Ohmagari N, Shin D, Brainard DM, Childs R, Flanigan T. et. al. N Engl J Med. 2020 Apr 10. [Epub ahead of publication]
[4] Structure of the RNA-dependent RNA polymerase from COVID-19 virus. Gao Y, Yan L, Liu F, Wang Q, Lou Z, Rao A, et al. Science. 10 April 2020. [Epub ahead of publication]
Links:
Coronavirus (COVID-19) (NIH)
Accelerating COVID-19 Therapeutic Interventions and Vaccines (NIH)
NIH Clinical Trial of Remdesivir to Treat COVID-19 Begins (National Institute of Allergy and Infectious Diseases/NIH)
Developing Therapeutics and Vaccines for Coronaviruses (NIAID)
COVID-19, MERS & SARS (NIAID)
NIH Support: National Institute of Allergy and Infectious Diseases
Electricity-Conducting Bacteria May Inspire Next-Gen Medical Devices
Posted on by Dr. Francis Collins
Technological advances with potential for improving human health sometimes come from the most unexpected places. An intriguing example is an electricity-conducting biological nanowire that holds promise for powering miniaturized pacemakers and other implantable electronic devices.
The nanowires come from a bacterium called Geobacter sulfurreducens, shown in the electron micrograph above. This rod-shaped microbe (white) was discovered two decades ago in soil collected from an unlikely place: a ditch outside of Norman, Oklahoma. The bug can conduct electricity along its arm-like appendages, and, in the hydrocarbon-contaminated, oxygen-depleted soil in which it lives, such electrical inputs and outputs are essentially the equivalent of breathing.
Scientists fascinated with G. sulfurreducens thought that its electricity had to be flowing through well-studied microbial appendages called pili. But, as the atomic structure of these nanowires (multi-colors, foreground) now reveals, these nanowires aren’t pili at all! Instead, the bacteria have manufactured unique submicroscopic arm-like structures. These arms consist of long, repetitive chains of a unique protein, each surrounding a core of iron-containing molecules.
The surprising discovery, published in the journal Cell, was made by an NIH-funded team involving Edward Egelman, University of Virginia Health System, Charlottesville. Egelman’s lab has had a long interest in what’s called a type 4 pili. These strong, adhering appendages help certain infectious bacteria enter tissues and make people sick. In fact, they enable bugs like Neisseria meningitidis to cross the blood-brain barrier and cause potentially deadly bacterial meningitis. While other researchers had proposed that those same type 4 pili allowed G. sulfurreducens to conduct electricity, Egelman wasn’t so sure.
So, he took advantage of recent advances in cryo-electron microscopy, which involves flash-freezing molecules at extremely low temperatures before bombarding them with electrons to capture their images with a special camera. The cryo-EM images allowed his team to nail down the atomic structure of the nanowires, now called OmcS filaments.
Using those images and sophisticated bioinformatics, Egelman and team determined that OmcS proteins uniquely fit into the nanowires’ long repetitive chains, spacing their iron-bearing cores at regular intervals to transfer electrons and convey electricity. In fact, bacteria unable to produce OmcS proteins make filaments that conduct electricity 100 times less efficiently.
With these cryo-EM structures in hand, Egelman says his team will continue to explore their conductive properties. Such knowledge might someday be used to build biologically-inspired nanowires, measuring 1/100,000th the width of a human hair, to connect miniature electronic devices directly to living tissues. This is one more example of how nature’s ability to invent is pretty breathtaking—surely one wouldn’t have predicted the discovery of nanowires in a bacterium that lives in contaminated ditches.
Reference:
[1] Structure of Microbial Nanowires Reveals Stacked Hemes that Transport Electrons over Micrometers. Wang F, Gu Y, O’Brien JP, Yi SM, Yalcin SE, Srikanth V, Shen C, Vu D, Ing NL, Hochbaum AI, Egelman EH, Malvankar NS. Cell. 2019 Apr 4;177(2):361-369.
Links:
Electroactive microorganisms in bioelectrochemical systems. Logan BE, Rossi R, Ragab A, Saikaly PE. Nat Rev Microbiol. 2019 May;17(5):307-319.
High Resolution Electron Microscopy (National Cancer Institute/NIH)
Egelman Lab (University of Virginia, Charlottesville)
NIH Support: National Institute of General Medical Sciences; National Institute of Allergy and Infectious Diseases; Common Fund
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