Cryo-electron microscope maps tumour cells
Looking at the mouths of cells
When Christina Paulino first encountered cryo-electron microscopy – a revolutionary technique that could magnify frozen specimens by a factor of a million – during her PhD in Zürich, no one took her interest in it seriously. The technique was still in its infancy then. ‘At the time it was a small field of study with just a few dedicated nerds. No one really took cryo-EM seriously. They called us “blob-ologists”.’
Light microscopy versus cryomicroscopy
An ‘ordinary’ light microscope magnifies by a factor of ten to a thousand. That’s like making a three-millimetre louse into a monster as big as a car. That’s large enough to study cells, but you can’t distinguish the structures in those cells.
Light microscopes can’t magnify beyond a factor of two thousand; the image will be too blurry.
But an electron microscope can magnify way beyond that factor. In fact, it can magnify to a factor of over a million. The aforementioned louse becomes a superbug the size of a continent. However, this level of magnification can only be reached under cryogenic conditions, so the specimen is flash-frozen and stored inside the microscope in a vacuum, at temperature of -180 degrees Celsius.
The name-calling wasn’t entirely unjustified. Cryo-EM was certainly promising, but hopelessly inaccurate. ‘Because you’re studying things that are so small, even the tiniest movement will blur the image.’
But Paulino didn’t relent. ‘There were many challenges to overcome, but that suited me just fine. I like a challenge.’ She also enjoyed the small community in the field. ‘People collaborate and share so much. It’s great to be a part of that.’
A revolution in resolution
Paulino was unsure at first whether she should continue in the field of cryo-EM. ‘But then, approximately four years ago, the revolution in resolution happened. Thanks to better cameras, the technique suddenly improved greatly. The hope that some cryo-EM specialists had had for years was realised.’
The images from the cryo-electron microscope are so sharp that the smaller proteins, which had always been invisible, were suddenly visible. Scientists could finally figure out the structure of these proteins, which ushered in an entirely new avenue of scientific possibilities.
Increasingly, universities are buying the million-dollar microscopes. ‘But there aren’t enough people who know how to work them.’ And so Paulino was scouted by Groningen to leave her post in Zürich. ‘I became an assistant professor, with many responsibilities.’
There aren’t enough people who know how to work the microscopes
It’s a great challenge for the structural biologist. ‘Now I have to prove that I’m worth it.’ She’s published several articles her first months here – in magazines such as Nature Structural & Molecular Biology – so she’ll probably be fine. ‘That’s really fast. So much is happening right now’, she says, proudly.
Medication
Paulino mainly uses her microscope to aid in the development of medication. To do so, she focuses on the special proteins on the outside of cells.
Resolution and computational power
Cryo-EM’s surge in popularity was due mainly to two breakthroughs. First, better cameras led to a clearer images. Because cryo-EM studies things that are so small, even the tiniest movement will blur the image beyond use. The fast cameras that have been developed over the past few years can compensate for these movements.
Second, the computational powers of computers have increased dramatically. Cryo-EM takes a photo of a frozen solution that contains proteins. You can take pictures of the same protein from various angles. The computer then combines all the angles to create a 3D image of the protein. Paulino’s group can generate up to two terabytes (two million megabytes) in one day. This takes a lot of storage and memory.
These cells can be compared to small, round creatures. The outside of the creatures are covered in holes that act sort of like mouths. These mouths allow substances to enter and exit the creature. If you want to starve the creature, you have to find a way to tape off its mouth. You can only do this when you know what this mouth looks like – and you need the right kind of tape.
Our cells are like these creatures, with holes made of proteins that allow substances to pass through. ‘I’m interested in these proteins’, Paulino explains. ‘If we know what they look like, we can develop medication that influences those gateways.’
Tumour cells
Over the past few months, Paulino has managed to map important proteins for tumour cells. A tumour is like an aggressive creature in the body. If you can manage to shut its mouth, the tumour will starve and ultimately, die.
‘Together with my colleagues Albert Guskov and Dirk Slotboom I studied one of these tumour cell openings responsible for the intake of the nutrient glutamine. Because we were able to map the structure of the transport protein, pharmacists can now try to find a medication that fits the mouths of these tumour cells.’
Paulino and her group have collaborated with colleagues over the past ten months to set up their research using the new generation of cryo-electron microscopes. ‘They already described a protein that was of interest to the field of biochemistry. We’ve mapped it and figured out the structure using cryo-EM.’
Pharmacists can now try to find a medication that fits the mouths of these tumour cells
In the future, however, she hopes to focus on her own research and profile proteins herself. Not just under the microscope, but also in the lab. ‘I am fascinated by membrane proteins, the doors to cells. I’m always trying to figure out what’s entering and exiting and how this happens.’
Healing
Paulino enjoys both fundamental and applied research. ‘It’s interesting to learn more about these channels. I want to understand how they work, and how they were created. There may not be a direct application for that kind of research, but scientists have discovered so much just because they were curious.’
She also acknowledges the use of applied research based on protein structures. ‘This structure is instrumental in how a protein works. It’s like knowing the blueprint of a machine. If we know what the structure of the proteins on the outside of cells look like, we can develop medication to cure diseases.’