The coronavirus sports a luxurious sugar coat. “It’s striking,” thought Rommie Amaro, staring at her computer simulation of one of the trademark spike proteins of SARS-CoV-2, which stick out from the virus’s surface. It was swathed in sugar molecules, known as glycans.
“When you see it with all the glycans, it’s almost unrecognizable,” says Amaro, a computational biophysical chemist at the University of California, San Diego.
Many viruses have glycans covering their outer proteins, camouflaging them from the human immune system like a wolf in sheep’s clothing. But last year, Amaro’s laboratory group and collaborators created the most detailed visualization yet of this coat, based on structural and genetic data and rendered atom-by-atom by a supercomputer. On 22 March 2020, she posted the simulation to Twitter. Within an hour, one researcher asked in a comment: what was the naked, uncoated loop sticking out of the top of the protein?
Amaro had no idea. But ten minutes later, structural biologist Jason McLellan at the University of Texas at Austin chimed in: the uncoated loop was a receptor binding domain (RBD), one of three sections of the spike that bind to receptors on human cells (see ‘A hidden spike’).
A hidden spike: A graphic showing the structure of the SARS-CoV-2 spike protein and its coating of glycans.
Source: Structural image from Lorenzo Casalino, Univ. California, San Diego (Ref. 1); Graphic: Nik Spencer/Nature
In Amaro’s simulation, when the RBD lifted up above the glycan cloud, two glycans swooped in to lock it into place, like a kickstand on a bicycle. When Amaro mutated the glycans in the computer model, the RBD collapsed. McLellan’s team built a way to try the same experiment in the lab, and by June 2020, the collaborators had reported that mutating the two glycans reduced the ability of the spike protein to bind to a human cell receptor1 — a role that no one has previously recognized in coronaviruses, McLellan says. It’s possible that snipping out those two sugars could reduce the virus’s infectivity, says Amaro, although researchers don’t yet have a way to do this.
Since the start of the COVID-19 pandemic, scientists have been developing a detailed understanding of how SARS-CoV-2 infects cells. By picking apart the infection process, they hope to find better ways to interrupt it through improved treatments and vaccines, and learn why the latest strains, such as the Delta variant, are more transmissible.
What has emerged from 19 months of work, backed by decades of coronavirus research, is a blow-by-blow account of how SARS-CoV-2 invades human cells (see ‘Life cycle of the pandemic coronavirus’). Scientists have discovered key adaptations that help the virus to grab on to human cells with surprising strength and then hide itself once inside. Later, as it leaves cells, SARS-CoV-2 executes a crucial processing step to prepare its particles for infecting even more human cells. These are some of the tools that have enabled the virus to spread so quickly and claim millions of lives. “That’s why it’s so difficult to control,” says Wendy Barclay, a virologist at Imperial College London.
Life cycle of the pandemic coronavirus: Infographic showing how the virus enters, adapts and exits from host cells.
Source: Hui (Ann) Liu, Univ. Utah; Graphic: Nik Spencer/Nature
Barbed and ready
It starts with the spikes. Each SARS-CoV-2 virion (virus particle) has an outer surface peppered with 24–40 haphazardly arranged spike proteins that are its key to fusing with human cells2. For other types of virus, such as influenza, external fusion proteins are relatively rigid. SARS-CoV-2 spikes, however, are wildly flexible and hinge at three points, according to work published in August 2020 by biochemist Martin Beck at the Max Planck Institute of Biophysics in Frankfurt, Germany, and his colleagues3.
That allows the spikes to flop around, sway and rotate, which could make it easier for them to scan the cell surface and for multiple spikes to bind to a human cell. There are no similar experimental data for other coronaviruses, but because spike-protein sequences are highly evolutionarily conserved, it is fair to assume the trait is shared, says Beck.
Slices through tomographic reconstructions of SARS-CoV-2 virions. Scale bars, 30 nm.
Cryo-electron tomography images of SARS-CoV-2 virions. (Scale bar: 30 nanometres.)Credit: B. Turoňová et al./Science
Early in the pandemic, researchers confirmed that the RBDs of SARS-CoV-2 spike proteins attach to a familiar protein called the ACE2 receptor, which adorns the outside of most human throat and lung cells. This receptor is also the docking point for SARS-CoV, the virus that causes severe acute respiratory syndrome (SARS). But compared with SARS-CoV, SARS-CoV-2 binds to ACE2 an estimated 2–4 times more strongly4, because several changes in the RBD stabilize its virus-binding hotspots5.
Worrying variants of SARS-CoV-2 tend to have mutations in the S1 subunit of the spike protein, which hosts the RBDs and is responsible for binding to the ACE2 receptor. (A second spike subunit, S2, prompts viral fusion with the host cell’s membrane.)
The Alpha variant, for example, includes ten changes in the spike-protein sequence, which result in RBDs being more likely to stay in the ‘up’ position6. “It is helping the virus along by making it easier to enter into cells,” says Priyamvada Acharya, a structural biologist at the Duke Human Vaccine Institute in Durham, North Carolina, who is studying the spike mutations.
The Delta variant, which is now spreading around the world, hosts multiple mutations in the S1 subunit, including three in the RBD that seem to improve the RBD’s ability to bind to ACE2 and evade the immune system7.
Restricted entry
Once the viral spikes bind to ACE2, other proteins on the host cell’s surface initiate a process that leads to the merging of viral and cell membranes (see ‘Viral entry up close’).
Viral entry up close: A graphic that shows the interaction between viral spike proteins and host receptors before viral entry.
Source: Janet Iwasa, Univ. Utah; Graphic: Nik Spencer/Nature
The virus that causes SARS, SARS-CoV, uses either of two host protease enzymes to break in: TMPRSS2 (pronounced ‘tempress two’) or cathepsin L. TMPRSS2 is the faster route in, but SARS-CoV often enters instead through an endosome — a lipid-surrounded bubble — which relies on cathepsin L. When virions enter cells by this route, however, antiviral proteins can trap them.
SARS-CoV-2 differs from SARS-CoV because it efficiently uses TMPRSS2, an enzyme found in high amounts on the outside of respiratory cells. First, TMPRSS2 cuts a site on the spike’s S2 subunit8. That cut exposes a run of hydrophobic amino acids that rapidly buries itself in the closest membrane — that of the host cell. Next, the extended spike folds back onto itself, like a zipper, forcing the viral and cell membranes to fuse.
Animated sequence of the SARS-CoV-2 virus merging its membrane with a cell.
An animation of the way SARS-CoV-2 fuses with cells.Credit: Janet Iwasa, University of Utah
The virus then ejects its genome directly into the cell. By invading in this spring-loaded manner, SARS-CoV-2 infects faster than SARS-CoV and avoids being trapped in endosomes, according to work published in April by Barclay and her colleagues at Imperial College London9.
The virus’s speedy entry using TMPRSS2 explains why the malaria drug chloroquine didn’t work in clinical trials as a COVID-19 treatment, despite early promising studies in the lab10. Those turned out to have used cells that rely exclusively on cathepsins for endosomal entry. “When the virus transmits and replicates in the human airway, it doesn’t use endosomes, so chloroquine, which is an endosomal disrupting drug, is not effective in real life,” says Barclay.
The discovery also points to protease inhibitors as a promising therapeutic option to prevent a virus from using TMPRSS2, cathepsin L or other proteases to enter host cells. One TMPRSS2 inhibitor, camostat mesylate, which is approved in Japan to treat pancreatitis, blocked viral entry into lung cells8, but the drug did not improve patients’ outcomes in an initial clinical trial11.
“From my perspective, we should have such protease inhibitors as broad antivirals available to fight new disease outbreaks and prevent future pandemics at the very beginning,” says Stefan Pöhlmann, director of the Infection Biology Unit at the German Primate Center in Göttingen, who has led research on ACE2 binding and the TMPRSS2 pathway.
Deadly competition
The next steps of infection are murkier. “There are a lot more black boxes once you are inside the cell,” says chemist Janet Iwasa at the University of Utah in Salt Lake City, who is developing an annotated animation of the viral life cycle. “There’s more uncertainty, and competing hypotheses.”
After the virus shoots its RNA genome into the cell, ribosomes in the cytoplasm translate two sections of viral RNA into long strings of amino acids, which are then snipped into 16 proteins, including many involved in RNA synthesis. Later, more RNAs are generated that code for a total of 26 known viral proteins, including structural ones used to make new virus particles, such as the spike, and other accessory proteins. In this way, the virus begins churning out copies of its own messenger RNA. But it needs the cell’s machinery to translate those mRNAs into proteins.
How a rampant coronavirus variant blunts our immune defences
Coronaviruses take over that machinery in many ways. Virologist Noam Stern-Ginossar and her team at the Weizmann Institute of Science in Rehovot, Israel, zoomed in on three mechanisms by which SARS-CoV-2 suppresses the translation of host mRNA in favour of its own. None are exclusive to this virus, but the combination, speed and magnitude of the effects seem unique, says Stern-Ginossar.
First, the virus eliminates the competition: viral protein Nsp1, one of the first proteins translated when the virus arrives, recruits host proteins to systematically chop up all cellular mRNAs that don’t have a viral tag. When Stern-Ginossar’s team put that same tag on the end of a host mRNA, the mRNA was not chopped up12.
Second, infection reduces overall protein translation in the cell by 70%. Nsp1 is again the main culprit, this time physically blocking the entry channel of ribosomes so mRNA can’t get inside, according to work from two research teams13,14. The little translation capacity that remains is dedicated to viral RNAs, says Stern-Ginossar.
Finally, the virus shuts down the cell’s alarm system. This happens in numerous ways, but Stern-Ginossar’s team identified one clear mechanism for SARS-CoV-2: the virus prevents cellular mRNA from getting out of the nucleus, including instructions for proteins meant to alert the immune system to infection. A second team confirmed this finding, and again pointed to Nsp1: the protein seems to jam up exit channels in the nucleus so nothing can escape15.
The global protective face mask market size is projected to reach USD 3.59 billion by 2027, exhibiting a CAGR of 7.1% during the forecast period.Growing Intensity of Air Pollution Worldwide to Boost the MarketOne of the central factors driving the protective face mask market growth is the intensification of air pollution and its effects on human health across globe.
Recent data from the WHO reveals that 90% of people breathe polluted air, with ambient and household air pollution resulting in 7 million deaths worldwide every year.
The main culprit is PM2.5 (particulate matter of less than 2.5 micro-meters), according to a report published by the World Bank, which penetrates the lungs and cardiovascular system, leading to life-threatening conditions such as stroke, lung cancer, respiratory infections, and heart disease.
Protective face masks are effective in filtering these pollutants and preventing inhalation of deadly air contaminants.
These masks are extensively used in urban areas, especially in developing countries, where energy consumption is high and pollution levels have reached inordinate levels.Surging demand for face protection masks to contain the spread of the COVID-19 infection will considerably augment the growth of this market, states Fortune Business Insights™ in its report, titled “Protective Face Mask Market Size, Share & Covid-19 Impact Analysis, By Type (Medical Face Mask {Surgical & Procedure, N-95 Respirators, and Others}, Respirator, and Others), By Usage (Disposable, and Reusable), and By End-Use (Healthcare, Oil & Gas, Mining, Construction, Manufacturing, and Others) and Regional Forecast, 2020-2027”.
This dire situation has gotten even more accentuated with countries reporting massive shortages of protective face masks.
The COVID-19 vaccine is helping us transition back to normal, but it does not mark the end of the pandemic.
The CDC guidelines reinforce the need for continued physical distancing, avoiding contact with those who have been exposed or are confirmed positive of COVID-19, wearing face masks in public and practicing hand hygiene, after vaccination, to help slow and stop the spread of COVID-19.The desired level of herd immunity, according to Dr. Anthony Fauci, is to have at least 75% vaccinated by the end of May 2021.
There are currently two COVID-19 vaccines authorized for use by the U.S. Food and Drug Administration: the Pfizer-BioNTech vaccine and the Moderna vaccine.The Pfizer vaccine is given in two shots, 21 days apart, and is authorized for use in people 16 years of age and older.
All viruses like SARS-CoV-2, have a unique genetic code.
Scientists took part of the virus's code, called the messenger RNA (mRNA) which tells our cells to make copies of a specific part of a protein unique to the spikes on the surface of the virus that causes COVID-19.
The immune system produces antibodies and activates T-cells, over the course of several days, to fight off what it thinks is an infection.
However, it said it still expects booster shots to be necessary ahead of the winter season as antibody levels are expected to wane.
It and rivals Pfizer and BioNTech have been advocating a third shot to maintain a high level of protection against Covid-19.During a second-quarter earnings call, Moderna CEO Stephane Bancel said that the company would not produce more than the 800 million to 1 billion doses of the vaccine that it has targeted this year.“We are now capacity constrained for 2021, and we are not taking any more orders for 2021 delivery,” he said.Moderna shares fell 3.6 per cent to around US$403.87 (S$545) in pre-market trading after closing at US$419.05 on Wednesday.That compares favourably with data released by rivals Pfizer and BioNTech last week in which they suggested their vaccine's efficacy waned around 6 per cent every two months, declining to around 84 per cent six months after the second shot.
Both the Moderna and Pfizer-BioNTech vaccines are based on messenger RNA (mRNA) technology.
실시간바카라"Our Covid-19 vaccine is showing durable efficacy of 93 per cent through six months, but recognize that the Delta variant is a significant new threat so we must remain vigilant,” Moderna chief executive Bancel said.The comment comes as public health officials across the world debate over whether additional doses are safe, effective and necessary even as they grapple with the fast-spreading Delta variant of the coronavirus.
Microarray Analysis Market Research Report: By Technology (DNA Microarray, PCR, NGS, SAGE, and Northern Blotting), By Consumables (DNA Chips, DNA Microarrays, Protein Microarrays, Cellular Microarrays, Chemical Compound Microarrays, Antibody Microarrays and others), By Services (Gene Profiling and Bioinformatics) and By Applications (Research, Drug Discovery and Diagnostic) - Global Forecast till 2027Abcam, Asterand Bioscience, IHC World, LLC, Novus Biologicals Llc (Acquired By Bio-Techne), Origene Technologies, Inc, Pantomics, Inc, Protein Biotechnologies Inc, US Biomax, Inc, Agilent Technologies, Illumina, Thermo Fisher Scientific, Merck are some of the prominent players at the forefront of competition in the Global Microarray Analysis Market and are profiled in MRFR Analysis.
It is a 2D array on a solid substrate, usually a glass slide or silicon thin-film cell, that assays large amounts of biological material using high-throughput screening miniaturized, multiplexed and parallel processing and detection methods.The concept and methodology of microarrays was first introduced and illustrated in antibody microarrays in 1983.
The DNA molecules attached to each slide act as probes to detect gene expression, which is also known as the transcriptome or the set of messenger RNA (mRNA) transcripts expressed by a group of genes.
But in the near future, as the research in this field progresses, tissue microarray will play an integral part in the diagnostic techniques in the field of cancer research and diagnosis.Request Free Sample Copy @ https://www.marketresearchfuture.com/sample_request/777Market Gaps:Tissue microarray is relatively new technique and a lot of research in tissue microarray is still going on.
As the results are not reliable, it creates a hindrance in the growth of the tissue microarray method.Besides this, microarrays are not recommended for certain types of studies.
In certain tumours such as glioblastoma, there is such marked heterogeneity within tumours that this feature may not be adequately captured in microarray studies.In addition, microarray analysis is not very useful to study rare or focal events, such as number of immune cells in tumours.
