If you thought you knew what high-res slow-motion video looks like, think again.
Researchers have recently captured images of biomolecular activity so slowly and in such detail that, lined up into a movie, they can reveal the activity of atoms, conceivably allowing us to peer into the world of biology on the world’s smallest scale.
Using the most brilliant X-ray flashes on the planet, an international team of scientists is reporting in the journal Science that they were able to capture images spanning just 40 femtoseconds (one femtosecond is a quadrillionth of a second), turning the blink of an eye into about a hundred million epic feature films. What’s more, they say they should be able to shorten the pulse duration further still, down to just a few femtoseconds.
They also achieved a resolution of 0.16 nanometers (a nanometer being a millionth of a millimeter), resulting in what they call the most detailed images of a biomolecule ever made using an X-ray laser. To put this size in context, the smallest atom, hydrogen, is about 0.1 nanometers.
The ability to watch proteins and enzymes at play does more than just give us insights into how these molecules perform various functions, biophysicist Marius Schmidt from the University of Wisconsin-Milwaukee told me by email. “If we know their function we can manipulate their function. We can completely shut them off, or enhance their functionality.”
The medical implications are far-reaching. Not only does this technique open the door to better observing the structure and function of enzymes, it is now possible, Schmidt said, to investigate, say, an important class of signaling receptors that plays key roles in cancer and cell differentiation – and to do so in real time at near-atomic resolution.
To test their technique, the researchers crystallized the photoactive yellow protein (PYP) that is a receptor for blue light and, because it has been so well studied, allowed the team to validate the new method. PYP plays a role in photosynthesis in some bacteria, and when it catches a blue photon it changes shape while harvesting that photo’s energy before returning to its original state.
While X-ray lasers have obvious limitations – vaporizing samples with their incredibly powerful pulses being generally problematic – they need to be short enough to catch these utlra-fast processes, and it turns out they’re short enough to produce a diffraction signal before the sample disintegrates. (This principle is called “diffraction before destruction” and was proven by a team at DESY a few years ago.)
The scientists accomplished these super short and intense X-ray flashes using the world’s most powerful laser, LCLS, at the Department of Energy’s SLAC National Accelerator Laboratory at Stanford. The short pulses allowed them to see not only how PYP morphs during the photocycle but even finer details, steps in the cycle that take less than a picosecond (a trillionth of a second), which is simply too fast to be observed using other approaches. They then assembled these tiny slivers of time into a nano movie.
Researchers have been making gains in imaging biomolecules at near-atomic resolution elsewhere as well. At the University of Illinois at Chicago, researchers recently wedged a biomolecule between sheets of one-atom-thick graphene to observe it in its natural, watery environment. Previously scientists have had to place samples in a liquid stage container wedged between thicker silicon nitrate in order to view the sample using electron microscopes. One scientist likened the improvement to looking through Saran wrap instead of thick crystal.
The graphene sheets also helped minimize radiation damage. Some calculations suggest that just to get a mere glimpse of a sample at such high resolution requires radiation levels 10 times higher than being 100 feet from a 10 megaton hydrogen bomb. Because they were able to continue using high-energy beams thanks to the deflection properties of graphene, the scientists were able to observe the protein ferritin, which regulates iron levels in both animals and plants.
Again, the approach could prove extremely valuable medically as the protein’s function plays a role in a wide range of disorders. “Defects in ferritin are associated with many diseases and disorders, but it has not been well understood how a dysfunctional ferritin works towards triggering life-threatening diseases in the brain and other parts of the human body,” the principal investigator said earlier this year.
The physicist who overcame several technical issues to make the graphene sandwich work says that because the approach is less expensive and easy to set up, once it’s mastered and easy to replicate it could “open up analysis of biological and other difficult-to-image samples to almost anyone with an electron microscope.”