Cells are the basic units of life – but many of their fundamental processes happen so fast and at such small length scales that current scientific tools and methods can’t keep up, preventing us from developing a deeper understanding.
Now, researchers with SLAC National Accelerator Laboratory, Stanford University, Cornell University and other institutions have developed a new approach for watching basic biological processes unfold. The approach, which combines cryogenic electron microscopes with methods developed in X-ray crystallography, could lead to improved medicines and a deeper understanding of cell division, photosynthesis and host-pathogen interactions, among other subjects.
“Many cellular processes happen on a millisecond timescale,” SLAC scientist and paper co-author Pete Dahlberg said. “With our new technique, we can poke a cell and then pick a moment in time that we want to snap a clear image of its response.”
Reimagining a powerful spray tool
For many decades, scientists have relied on imaging techniques known as cryogenic electron microscopy (cryo-EM) and cryogenic electron tomography (cryo-ET) to see inside of cells, proteins, and other organisms and molecules. Both techniques use electron microscopes to capture snapshots of flash-frozen samples, which have revealed cellular structures in extraordinary detail. These approaches involve putting a sample on a thin small disk known as an electron microscopy grid and plunging it into a cryogenic liquid to freeze it very rapidly. This is great at preserving cellular samples in their native state, but the frozen snapshots don’t tell researchers much about dynamics. It is sort of like trying to learn dance moves by taking random images of someone dancing.
Currently in similar cryo-ET experiments, researchers hand-mix cell samples in order to take images of them in response to a stimuli. But hand-mixing takes time, kind of like mixing pancake batter by hand instead of with an electric mixer, meaning that experimenters can only observe changes in an organism at about ten second intervals – hundreds of times longer than many important processes take.
“When you hand-mix and freeze cells in cryo-ET experiments, you are often too slow to capture the changes you really care about. That can limit your ability to understand important biological processes,” SLAC researcher and paper co-author Cali Antolini said.
Researchers therefore turned to a spray nozzle device that is often used at X-ray free-electron laser (XFEL) and synchrotron facilities to mix samples for crystallography experiments. The device, known as a mixing injector coupled Gas Dynamic Virtual Nozzle (GDVN), is often used to study molecular movements that occur on extremely short timescales, like femtoseconds after activation with light or on millisecond to second timescales using chemical mixing, at XFELs like SLAC’s Linac Coherent Light Source (LCLS).
Read more on SLAC website
Image: A graphic representation of the spray nozzle device. The sample cells (green) mix with the simulant solution as the cells travel from left to right, out of the spray nozzle.
Credit: Greg Stewart/SLAC National Accelerator Laboratory