Proteins are the building blocks of viruses, cells, and enzymes. Fully understanding them requires access to imaging their often very rapid motion. An international team of researchers have recently published a study showing that the ultrashort X-ray pulses of the FemtoMAX beamline are enough for making images of, in this case, stationery, protein crystals with high resolution. It is an essential step towards in the future, catching the proteins elusive dance and contribute to, for example, predictions of how a mutated virus would infect cells.
Protein molecules have a structure – a sequence of amino acids, and a folding pattern. The structure is possible to access by letting X-rays scatter in the sample and interpreting the resulting pattern on the detector. If your setup is good enough, you can see the structure with a high resolution and clarity. The structure is, however, only part of the protein function. A movement between different states is often needed, such as opening and shutting a door in the cell membrane. With the ultrashort X-ray pulses at FemtoMAX, it will be possible to take clear snapshots of the process. Like shooting a football game with a fast shutter. Ultrashort pulses are often associated with an X-ray source type called free-electron laser or FEL for short.
“The most important result of the study is that we can determine high-quality protein crystal structures at the FemtoMAX beamline. Their quality and resolution are similar to what can be seen at specialized macromolecular X-ray crystallography beamlines and intense X-ray free-electron lasers,” says prof Gergely Katona, University of Gothenburg. “This study paves the way for using the FemtoMAX beamline for studying very fast processes in protein crystals. Such studies so far were associated only with X-ray free-electron lasers.”
Professor Katona and his team are carrying out their research with the goal of better theoretical models in sight. The models could, for example, play an important role in predicting the effect of mutating viruses.
“Our studies aim to explore the general role of fast motions in proteins that happen all the time. We expect that the principle is the same in all structured proteins and we hope that we will develop a model of proteins which can both predict and explain the nature of these motions,” explains Katona. “The benefit of better protein models is that in the future, fewer experiments will be necessary, and we could more confidently rely on our predictions. For, example, if a new mutation of a virus is discovered, we could potentially foresee how this affects the structure and binding of the virus at much earlier stage.”
A challenge to keep in mind when studying proteins using X-rays is that the harsh radiation may burn the fragile biomolecules and affect the results. Therefore FemtoMAX is an exciting complement to FELs.
“The FemtoMAX beamline is gentle compared to X-ray free-electron lasers. We can be reasonably sure that protein is not damaged substantially by the X-ray beam, and we can record many images from the same sample. It is advantageous to look at a sample, do something with it, and look at it again. One can also repeat this process many, many times at the FemtoMAX beamline,” continues Katona. “At free-electron lasers, used at their maximum intensity, a sample can only be used once before it is destroyed and every new sample is different. It can be hard to tell what caused the differences in the structure, natural sample to sample variation or the changes in the environment that we want to test.”
The future for protein research at FemtoMAX looks bright, but there are many things to keep developing, something the researchers think is positive.
“It is fantastic to have the possibility to tweak so many things and it is always a pleasure to find something that works better. It keeps our job always interesting,” concludes Katona. “The repetition rate of the experiment is a key property of the beamline. We started at 2 Hz, we expect to continue with 10 Hz, but we already dream about 100Hz. The higher the repetition rate, the higher time and image resolution we can obtain. If we find a better place for the X-ray camera we may also improve the molecular image quality, but there are many considerations to be done.”
Maja Jensen, Viktor Ahlberg Gagnér, Juan Cabello Sánchez, Åsa U. J. Bengtsson, J. Carl Ekström, Tinna Björg Úlfarsdóttir, Maria-Jose Garcia-Bonete, Andrius Jurgilaitis, David Kroon, Van-Thai Pham, Stefano Checcia, Hélène Coudert-Alteirac, Siawosch Schewa, Manfred Rössle, Helena Rodilla, Jan Stake, Vitali Zhaunerchyk, Jörgen Larsson, and Gergely Katona, High-resolution macromolecular crystallography at the FemtoMAX beamline with time-over-threshold photon detection, J. Synch. Rad 28, 62 (2021), DOI: 10.1107/S1600577520014599