A 400-year-old solar mystery, mass-producing recombinant proteins, and safer X-rays

Solving a puzzle Galileo struggled with, using MSG and ethanol to produce recombinant proteins, and a step closer to gentler medical imaging.

This illustration lays a depiction of the sun’s magnetic fields over an image captured by NASA’s Solar Dynamics Observatory. The complex overlay of lines shows the ways the sun’s magnetism changes in response to the constant movement on and inside the sun.  | Photo Credit: NASA/SDO/Lockheed Martin Solar and Astrophysical Laboratory 

Solving a 400-year-old solar mystery

AN international team of researchers led by Geoffrey Vasil of Edinburgh University is getting closer to solving a 400-year-old solar mystery that even Galileo Galilei had tried to understand.

Since first observing the sun’s magnetic activity, astronomers have struggled to pinpoint where the process originates. Now, after running a series of complex calculations on a NASA supercomputer, the researchers discovered that the magnetic field is generated about 30,000 km below the sun’s surface. The finding contradicts previous theories that suggested that the phenomenon had deep origins, beginning more than 2,00,000 km below. The work was published in the journal Nature.

The new finding will help astronomers get a better understanding of the sun’s dynamic processes, which could lead to more accurate forecasting of solar flares and solar storms like the one in May that released beautiful, extended views of the Northern Lights. Although the May storms did not result in any serious damage to the earth’s infrastructure such as electricity grids and telecommunication networks, including GPS navigation tools and earth-orbiting satellites, more powerful storms can cause severe destruction.

“This work proposes a new hypothesis for how the sun’s magnetic field is generated that better matches solar observations and, we hope, could be used to make better predictions of solar activity,” said Daniel Lecoanet of Northwestern University, an expert in astrophysical fluid dynamics and the paper’s co-author.

Over the years, physicists made significant progress in understanding the origins of the solar dynamo—the physical process that generates the magnetic field—but limitations remained (see “Light on sunspots”, Frontline, January 11, 2013). Theories suggesting that the dynamo has a deep origin predict, for example, solar features such as strong magnetic fields at high latitudes, which have never been observed.

Vasil’s team developed new, state-of-the-art numerical simulations to model the sun’s magnetic field. Unlike previous models, the new model accounts for torsional oscillations, a cyclical pattern of how gas and plasma flow within and around the sun. Because the sun is not solid like the earth and the moon, it does not rotate as one body; its rotation varies with latitude. Like the 11-year solar magnetic cycle, torsional oscillations also experience an 11-year cycle.

“Because the wave has the same period as the magnetic cycle, it has been thought that these phenomena were linked,” Lecoanet said. “However, the traditional ‘deep theory’ does not explain where torsional oscillations come from. An intriguing clue is that these are only near the surface of the sun. Our hypothesis is that the magnetic cycle and the torsional oscillations are different manifestations of the same physical process.”

From their numerical simulations, the researchers found that the new model provided a quantitative explanation for properties observed in the torsional oscillations. The model also explained how sunspots follow patterns of the sun’s magnetic activity, another detail missing from the deep origin theory.

Using the yeast Pichia pastoris for safe mass production of recombinant proteins.  | Photo Credit: Neetu Rajak/P.N. Rangarajan’s Lab, IISc, Bengaluru

Novel method to mass-produce recombinant proteins

MASS production of recombinant proteins, such as vaccine antigens, insulin, and monoclonal antibodies, is usually done using what are called cell “factories” where expression of the protein of interest is achieved by the manipulation of gene expression in an organism to produce large amounts of a recombinant gene.

Commonly used production systems include those derived from organisms such as bacteria, baculovirus/insect cells, mammalian cells, and yeast in which modified cells of these systems are grown in large bioreactors. The most widely used organism is the yeast Pichia pastoris (now called Komagataella phaffii). It contains a unique promoter, a specific gene region, that can be activated by methanol. This promoter codes for an enzyme called alcohol oxidase.

But the disadvantage of this process is that it needs methanol to induce gene expression. Methanol is flammable and toxic to cells if not thoroughly removed as it can produce harmful by-products that can damage the recombinant proteins. Researchers at the Indian Institute of Science (IISc), have developed an alternative safer process that relies on monosodium glutamate (MSG), a common food additive. The work was published in the journal Microbial Cell Factories.

The researchers found that MSG can activate a different promoter in the yeast genome that codes for an enzyme called phosphoenolpyruvate carboxykinase whose activation with MSG led to protein production similar to what is achieved with methanol.

Optimising the cell culture medium for this new and untested process was challenging. For a long time, the IISc’s press release said, the yeast cells grew poorly and produced very little recombinant protein.

The group figured out that using MSG alone was not enough and, after supplementing the culture with several other compounds, eventually found that ethanol did the trick. It helped the cells grow faster, which increased the amount of recombinant protein produced. Ethanol is safer for yeast cells than methanol as it does not produce toxic by-products.

The team tested the process with the SARS-CoV-2 receptor-binding domain and found that their new system produced twice the amount of antigen compared with the methanol-induced process.

The researchers hope that this novel expression system can be used to mass-produce valuable proteins, including milk and egg proteins, baby food supplements, and nutraceuticals, apart from therapeutic molecules. The team is also looking for industry collaborators to scale up the system for mass production.

An inorganic caesium-lead-bromide based direct-conversion X-ray CMOS detector.  | Photo Credit: Yongshuai Ge/SIAT

A step towards safer X-rays for medical imaging

A TEAM of researchers from the Shenzhen Institute of Advanced Technology (SIAT) of the Chinese Academy of Sciences and Central China Normal University has developed a high-performance perovskite X-ray complementary metal-oxide-semiconductor (CMOS) detector for medical imaging. The work was published recently in Nature Communications.

X-ray imaging is vital for the diagnosis and treatment of cardiovascular diseases and cancer. Direct-conversion X-ray detectors made of semiconductor materials exhibit superior spatial and temporal resolution at lower radiation doses compared with indirect-conversion detectors made of scintillator materials. However, currently available semiconductor materials, such as silicon, amorphous selenium, and cadmium-zinc telluride/cadmium telluride, are not ideal for general X-ray imaging due to their low X-ray absorption efficiency or high costs.

Perovskite is a promising alternative to conventional semiconductor materials. However, the feasibility of combining it with high-speed pixelated CMOS arrays is still unknown. To address this issue, researchers developed a direct-conversion X-ray detector fabricated with a 300 micrometre thick inorganic caesium lead bromide (CsPbBr₃) perovskite film printed on a dedicated CMOS pixel array.

Experimental X-ray 2D imaging results showed that the proposed perovskite CMOS detector can achieve a very high spatial resolution (5.0 line pairs, or lp/mm; the hardware limit is 6.0 lp/mm) and low-dose (260 nanogray) imaging performance. Moreover, 3D CT imaging was also validated with the proposed detector at a fast signal readout speed of 300 frames/s.

“Our work shows the potential of lead halide perovskites in revolutionising the development of state-of-the-art X-ray detectors with significantly enhanced spatial resolution, readout speed, and low-dose detection efficiency,” said Yongshuai Ge of the SIAT. “This paves the road for medical X-ray imaging applications to become gentler and safer in the future.”