X-ray laser opens new view on Alzheimer proteins

Graphene enables structural analysis of naturally occurring amyloids.

On the ultra-thin, extremely regular layer of graphene, the fibrils align themselves in parallel in large domains. The intense X-ray light from the X-rax free-electron laser LCLS at the SLAC National Accelerator Center enabled the researchers to gain partial information about the fibril structure from ensembles of just a few fibrils. Illustration: Greg Stewart/SLAC National Accelerator Laboratory
On the ultra-thin, extremely regular layer of graphene, the fibrils align themselves in parallel in large domains. The intense X-ray light from the X-rax free-electron laser LCLS at the SLAC National Accelerator Center enabled the researchers to gain partial information about the fibril structure from ensembles of just a few fibrils. Illustration: Greg Stewart/SLAC National Accelerator Laboratory

DESY scientists have used a powerful X-ray laser to gain insights into the structure of different amyloid samples. Using x-ray laser, they discovered filamentous biomolecules are mainly responsible for diseases such as Alzheimer’s and Parkinson’s.

Using the technique, they analyze the patterns somewhat similar to those obtained by Rosalind Franklin from DNA in 1952, which led to the discovery of the well-known structure, the double helix.

According to scientists, the technique could help in observation of individual amyloid fibrils, the constituents of amyloid filaments.

Amyloids are long, ordered strands of proteins which consist of thousands of identical subunits. While amyloids are believed to play a major role in the development of neurodegenerative diseases, recently more and more functional amyloid forms have been identified.

DESY’s Carolin Seuring, a scientist at the Center for Free-Electron Laser Science (CFEL) said, “The ‘feel-good hormone’ endorphin, for example, can form amyloid fibrils in the pituitary gland. They dissolve into individual molecules when the acidity of their surroundings changes, after which these molecules can fulfill their purpose in the body.”

“Other amyloid proteins, such as those found in post-mortem brains of patients suffering from Alzheimer’s, accumulate as amyloid fibrils in the brain, and cannot be broken down and therefore impair brain function in the long term.”

“Our aim is to understand the role of the formation and structure of amyloid fibrils in the body and in the development of neurodegenerative diseases. The structural analysis of amyloids is complex, and examining them using existing methods is hampered by differences between the fibrils within a single sample.”

Scientists used X-ray free-electron laser LCLS at the SLAC National Accelerator Laboratory in the U.S. The X-ray laser, trillions of times more intense than Franklin’s X-ray tube, opens up the capacity to look at singular amyloid fibrils, the constituents of amyloid fibers. With such effective X-ray beams, any superfluous material can overpower the flag from the imperceptibly little fibril test.

Ultrathin carbon film – graphene – tackled this issue to enable amazingly touchy examples to be recorded. This denotes a critical advance towards concentrate singular particles utilizing X-ray lasers, an objective that basic scientists have for quite some time been seeking after.

Securing explained, “A major part of our understanding about amyloid fibrils is derived from nuclear magnetic resonance (NMR) and cryo-electron microscopy data. When you are working with samples that are as heterogeneous as amyloids, though, and also when observing the dynamics of fibril formation, the existing methods reach their limits.”

In order to gain access to structure information of such heterogeneous samples in the future, the team opted for a new experimental approach. Instead of suspending the individual amyloids in a carrier fluid like a water jet the scientists placed it on an ultrathin solid carrier made of graphene, in which carbon atoms are arranged in a hexagonal pattern rather like an atomic honeycomb.

Professor Henry Chapman of CFEL, who is a lead scientist at DESY said, “This sample support has a double benefit. For one thing, graphene is just a single layer of atoms thin and in contrast to a carrier, fluid hardy leaves a trace in the diffraction pattern. For another thing, its regular structure makes sure the protein fibrils all align in the same direction – at least in larger domains.”

“The diffraction patterns of multiple fibrils overlap and reinforce one another, much like in a crystal, but there is virtually no disruptive background scattering as in the case of a carrier fluid. This method allows diffraction patterns to be obtained from fewer than 50 amyloid fibrils so that the structural differences emerge more clearly. We have observed characteristic asymmetries in our data which suggest that our technique could even be used to determine the structure of individual fibrils.”

Scientists tested their method on samples of the tobacco mosaic virus, also first examined by Rosalind Franklin, and which forms filaments of a structure that is now known in great detail. The test did, in fact, provide structural data about the virus with an accuracy of 0.27 nanometres (millionths of a millimetre) – corresponding to a resolution almost on the scale of a single atom. The examination of distinctly smaller amyloid fibrils made of endorphin as well as amyloid fibrils made of the hormone bombesin, which is involved among other things in certain types of cancer, also provided some structural information, with an accuracy of 0.24 nanometers.

Co-author Mengning Liang, a scientist at SLAC said, “The CXI instrument at LCLS provided an exceptionally bright, nanofocus beam that allowed us to extract data from such a small number of fibers. Fibrils are a third category of samples that can be studied this way with X-ray lasers, in addition to single particles and crystals. In some regards, fibrils fit between the other two: they have regular, recurring variations in a structure like crystals, but without the rigid crystal structure.”

The study is detailed in the journal Nature Communications.