“Novel protein structure and binding properties may explain Spanish flu virulence and how to prevent another pandemic”
This week, the World Health Organization will hold a consultation meeting — only its fourth ever – to discuss the latest data, technologies and developments in flu prevention and response.
Flu sickens three to five million people a year around the world, killing hundreds of thousands of them. Each year, experts sort through global data to identify the flu strains that pose the most likely upcoming threat. Vaccines are then tailored to defend against those strains. Winnowing down to three or four flu strains to guard against isn’t easy, and miscalculations can mean an unprotected population and a higher-than-average death rate. That’s why researchers put intense efforts into predicting the flu strains that are coming and mining clues from flu viruses that have come and gone.
Bits of new information can make an outsized impact, especially when the discovery illuminates mechanisms that increase the virulence of a flu strain. Just such a discovery came from a team led by Chad Petit, PhD. Petit teaches and conducts research at the Central Alabama High-Field NMR Facility at the University of Alabama at Birmingham (UAB). The lab houses several Bruker NMR instruments including the 600 MHz, 700 MHz and 850 MHz.
For his research, Petit took on a behemoth of a flu, the one that caused the 1918 pandemic and, by some estimates, afflicted thirty percent of the world’s population and killed up to forty million people. More people died from the 1918 flu than from World War I. The disease caused so much fear, many countries censored news coverage. In fact, the 1918 flu is often called the “Spanish” flu, not because it began in Spain, but because news outlets in Spain were not censored and were able to report on the pandemic.
The intense virulence of the 1918 strain caught Petit’s attention. He set out to uncover just how the 1918 virus became so widespread and deadly. Using advanced technology and techniques, including NMR spectroscopy, Petit studied the structure and binding properties of the 1918 Spanish flu and compared his findings with the 1972 Udorn flu.
Petit and colleagues reported the results in, “Structural basis for a novel interaction between the NS1 protein derived from the 1918 influenza virus and RIG-I,” published in the Nov. 7, 2015, Structure. The research was conducted at UAB and the National Magnetic Resonance Facility at Madison, University of Wisconsin-Madison, where there is a range of Bruker technology.
This research showed, for the first time, that a non-structural protein from the 1918 flu virus, NS1, doesn’t just interact with RIG-I, it binds directly with it. RIG-l is a vigilant monitor of flu virus infection. Normally, NS1 floods into cells and battles the immune system. In response, RIG-I sparks the immune system into high gear. But in the case of the 1918 flu, NS1 binds to RIG-I and interferes with the normal immune response. This specific interference may explain, in part, why the 1918 flu was so deadly.
Not all NS1 binds with RIG-I. The researchers studied action in the 1972 Udorn NS1 proteins and observed that NS1 did not bind to RIG-I. That means binding between NS1 and RIG-I depends on the specific flu strain.
Petit’s team went further and analyzed the section of the NS1 in 1918 flu that binds to RIG-I. They dubbed that section NS1 RNA binding domain, or 1918 NS1RBD. By comparing it to the previously identified structure of Udorn NS1 protein, they spotted the differences in amino acids that may make it possible for 1918 NS1 proteins to bind to RIG-l. Now scientists can describe the location and structure of 1918 NS1RBD.
During the study, researchers noticed salt bridges but only in the 1918 strain. They found that these salt bridges change 1918 NS1RBD by creating intramolecular distances that are larger than average between two of the protein helices in 1918 NS1 as compared to the distances in Udorn NS1 proteins. That increased distance may assist the interaction between 1918 NS1RBD and RIG-l. With more investigation, that distance may prove to be a weak link in the structure that is vulnerable to anti-flu drugs.
Next the researchers focused on the structure of RIG-I and honed in on the section that binds to 1918 NS1RBD. They discovered the bond occurs at the second caspase activation and recruitment domain of RIG-I, or RIG-ICARD2. In the future, the details of the structure of RIG-ICARD2 may serve as a target for drug discovery.
Another investigatory path is finding ways to use sequence data to predict the virulence of flu strains. Since predicting which flu viruses pose the greatest threat is key to designing yearly vaccines, improvement in evaluating the virulence of strains could increase the efficacy of yearly vaccines. That could go a long way in lessening the impact of flu and avoiding another pandemic as deadly as the one caused by the 1918 Spanish flu.