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“Seeing is believing.”
Text: Christian Heuss
Ben Engel wants to understand the solar power stations of life: chloroplasts. He uses high-tech microscopes to watch them at work and get to the bottom of carbon fixation.
“Every experiment is like a journey into undiscovered territory,” says Ben Engel, casting his gaze across the rolling hills of Baden through the large glass window of his corner office at the Biozentrum. In terms of research, his work focuses on tiny details. The structural biologist uses a technique known as cryo-electron tomography to study the solar power stations of life: chloroplasts.
“I’m a very visual person,” explains the 43-year-old Californian, who moved into the Biozentrum with his research group in 2022. As a student in San Francisco and Berkeley, he says, the methods of biochemistry were always a bit too abstract for him. He was, however, irresistibly drawn to microscopy because it allowed him to watch cellular processes at work. “Seeing is believing,” says Engel with his Californian accent and a broad grin. For him, it’s easier to understand what he can see with his own eyes.
Over 10 years ago, this principle brought Engel to the Max Planck Institute of Biochemistry in Munich. It was there that Wolfgang Baumeister developed cryo-electron tomography, a technique that is currently revolutionizing modern cellular biology. Researchers can use the technique to examine cellular processes down to the level of protein components.
Nature’s solar panels.
Ben Engel’s scientific interests center around one of the most important biological processes on the planet: photosynthesis. Plants, algae and cyanobacteria use the energy of sunlight to split water, powering the generation of biological energy while producing oxygen: a waste product for the plant but a prerequisite for humans and many other species on our planet. In a process known as carbon fixation, photosynthetic organisms then use their light-generated energy to convert CO2 into sugar, which directly or indirectly feeds most of the life on Earth.
We begin our tour of his laboratory in the algae room, where dozens of glass vessels containing green, red and slightly brownish liquids stand on slowly rotating plates. Each vessel carries the name of the algae species on a hand-written adhesive strip.
Not only are algae practical research objects by virtue of the fact that they are easy to collect and culture, but they also account for a quarter of global carbon fixation via photosynthesis. Many of the individual photosynthetic proteins are well understood, says Engel, though there are still questions regarding how these proteins are organized together inside the chloroplast in order to efficiently harvest sunlight. “We’re essentially studying nature’s solar panels.”
In the process, Engel has indeed observed structural differences between different species of algae. He also suspects the existence of geographical adaptations. In collaboration with the European Molecular Biology Laboratory TREC expedition, his group is currently comparing the structures of the “solar panels” in algae collected from different sea coasts across Europe.
Stopping time.
One door down, a colleague is using a pipette to apply a droplet of algae cells to a tiny copper mesh with a diameter of just three millimeters. A machine then rapidly cools the algae to a temperature below -182°C in liquid ethane. This freezing process takes place so quickly that no water crystals can form, with the water in and around the algae cell solidifying into a glass-like state. “It’s as if time suddenly stood still,” says Engel.
Before the researchers can examine the inside of algae cells, they must first open a window into the cell’s interior, explains Engel as we enter a slightly darkened room. The tool for opening this window is a cryo-scanning electron microscope that is also equipped with a focused ion beam. A screen displays the magnified copper mesh on which the frozen algae cells are sitting, and a doctoral student uses the ion beam to carefully cut away at the cells as if using a scalpel. “She’s removing the frozen surface layer by layer to form a wafer-thin window,” explains Engel.
The thinned frozen cell is then ready for final imaging in a transmission electron microscope that can visualize individual organelles, membranes and protein structures. By rotating the sample and imaging it from multiple angles, the researchers obtain a 3D view of fine molecular details inside the cell.
“When I first saw this wealth of detail over 10 years ago, it was like a revelation for me,” says Engel. “I could finally see the cell’s molecular secrets with my own eyes!” Since then, he hasn’t relinquished his thirst for discovery.
Carbon fixation to tackle the climate crisis.
Engel’s enthusiasm for his area of research is infectious, but is this high-tech basic research also valuable to society? “Absolutely,” he says without hesitation. “It’s not possible to apply knowledge before we’ve found it.”
In the case of Ben Engel’s group, they seek to understand how photosynthesis adapts to changing environmental conditions and efficiently captures CO2 from the atmosphere. For example, he says that insights into the photosynthesis apparatus could become a key part of the puzzle for tackling the current climate crisis, with applications including the cultivation of food crops that could fix carbon more effectively or cope with our changing climate. Engel is quick to add that human-caused CO2 emissions must be greatly reduced.
There is another aspect that’s very close to his heart. As a scientist, he wants to understand how the world works, but he believes it is just as important to pass these insights on to society in a comprehensible form. “If we don’t, who will?”
Ben Engel was born in northern California in 1981 and has been assistant professor at the Biozentrum of the University of Basel since 2022. After studying cellular transport processes for his doctoral dissertation at the University of California, San Francisco (USA), Engel focused his research on the inner structure of chloroplasts at the MPI of Biochemistry in Munich from 2011 onward. He has led his own research group since 2019 and is an EMBO Young Investigator. In 2022, Engel received a prestigious Consolidator Grant from the European Research Council (ERC) for his innovative projects in Basel and received funding from the State Secretariat for Education, Research (SERI). He is married to a chemist and has three children.
More articles in this issue of UNI NOVA (May 2024).