Representative image: CDC/Pexels.
Cryo-electron microscopes (CEMs) are at the cutting edge of modern structural biology. These machines have been instrumental in scientists’ discovery of the structures of various important biomolecules, their roles in different life-functions and diseases, and subsequently in attempts to develop treatments.
Currently, India has two CEMs. The first national facility was established in September 2017 at the National Centre for Biological Sciences, followed by the Advanced Centre For CEM at the Indian Institute of Science. Both institutes are in Bengaluru and both facilities were funded by the Department of Biotechnology.
A CEM is an EM – a microscope that uses electrons instead of photons, the particles of light, to visualise a sample under study. Since electrons have a shorter wavelength, they are able to resolve smaller features. The ‘C’ of CEM requires the sample to be cryogenically frozen so that it doesn’t have to be placed in a vacuum. Water evaporates in a vacuum, which could potentially destroy wet tissue.
These machines typically cost Rs 40-60 crore each.
Sandeep Verma, the secretary of the Science and Engineering Research Board, recently said the board had approved four new national CEM facilities across India. He believes these facilities will help create a deep knowledge base and skills for CEM research in India to establish global competitiveness in structural biology, enzymology, ligand/drug discovery, and to combat new and emerging diseases.
Even during the COVID-19 pandemic, “there has been so much to understand about the virus and its spike protein. In India, we could not do it since we had only two CEM machines,” said Arun Shukla, an associate professor in the department of biological sciences and bioengineering, IIT Kanpur. “Even if someone is really interested in studying them, they couldn’t have been able to access the facilities due to the lockdown.”
“If we want to prepare for the next pandemic, we should have at least ten CEM facilities across the county.”
The early decades of structural biology were dominated by techniques like nuclear magnetic resonance, X-ray crystallography and electron microscopy. Using them, scientists were able to deduce the structures of important macromolecular structures like ribosomes, G-protein coupled receptors, ion-channel proteins and many viruses.
The case of the electron microscope readily illustrates the need to look for even better microscopy techniques. To resolve the shape and structure of a molecule, an electron microscope uses focused, high-energy beams of electrons – the same way an optical microscope uses lenses to focus photons. If a scientist needs a higher resolution image, the beams need to be more energetic as well. But beyond a certain point, the beams are likely to become too strong to image the sample without destroying it at the same time.
While negative-staining electron microscopes could resolve features 30-40 Å wide (1 Å is 10-10 m), the CEMs of today can reach up to 1-4 Å.
In the early 1980s, Jacques Dubochet and his team at the University of Lausanne, Switzerland, plunged a biological sample they had into liquid ethane at around -180º C before loading it into an electron microscope. To their surprise, they found that molecules in the sample retained their original shape, allowing the team to image it at higher resolutions than before.
Taking advantage of this improvement, Richard Henderson and his team at the MRC Laboratory of Molecular Biology in Cambridge, UK, recorded the first-ever atomic-resolution images of a protein using CEM in 1990. Shortly after, Joachim Frank and his team in the US developed image-processing tools and software required to optimise this technique for use by biologists in the lab. The trio of men received the Nobel Prize for chemistry in 2017 for this work.
“Cryo-EM allows us to visualise single viruses, several macromolecules and very small proteins,” Shukla said. “CEM structure also helps us predict potential drugs that may have the ability to bind to target proteins. Earlier, this was only possible with X-ray crystallography.”
Since the 1990s, CEM technology has evolved rapidly to support superior sample preparation methods, automatic data acquisition and algorithms to determine structures – in addition to better microscope hardware. For example, direct electron detectors like the K3 camera have replaced cameras with charge-coupled devices. Engineers have also developed built-in mechanisms to automatically maximise a target, allowing scientists to achieve super-high resolutions and easing the task of microscopists in labs.
However, none of this means CEM technology has reached its destination. For one, pharmaceutical companies need atomic-resolution microscopy to decipher the complete structures of proteins and other biomolecules, and thus accelerate the drug discovery process. For another, there are opportunities to develop even faster algorithms to reveal the structure of a molecule from a given CEM image.
In light of these opportunities, installing new CEMs as soon as possible will hold the door open for India’s scientists and students to not only pursue cutting edge research but also possibly get a head start on biomedical technologies of the future.
Chinmaya K.V. is a freelance science writer interested is in science communication through writing, interviews and photography.