Researchers Capture Protein Tangle Formation in Real-Time

Protein tangles, known as amyloid-beta (A-beta) aggregates, are most famously linked to neurodegenerative illnesses like Alzheimer's. Nevertheless, despite its frequent attention, scientists have not been able to comprehend how A-beta assembles and disassembles fully.

The way A-beta behaves in a variety of environments, including the human brain, is elusive. There’s an understanding of growth and decay that isn’t fully fleshed out”

Brian Sun, Study First Author, Electrical Systems and Engineering, Washington University in St. Louis

The recent research conducted by Sun and associates in the Preston M. Green Department of Electrical & Systems Engineering at WashU's McKelvey School of Engineering, which Matthew Lew leads, is going to change that.

Sun and colleagues achieved a first: they could measure the girders of the protein conglomeration, the underlying amyloid fibril beta-sheet assemblies, in real-time. Previous studies using high-resolution microscopy have only obtained still images.

We wanted to look specifically at dynamics of the underlying structure of A-beta that could be responsible for the changes we’re seeing, not just changes in the overall shape.”

Brian Sun, Study First Author, Electrical Systems and Engineering, Washington University in St. Louis

Lew compared it to Lego bricks, pointing out that while modern imaging technology can display an entire Lego building, it cannot show how the individual bricks are arranged.

The individual proteins are always changing in response to their environment. It is like having certain Lego bricks causing other bricks to change their shape. The changing architecture of the proteins and the assembled aggregates together leads to the complexity of neurodegenerative disease.”

Matthew Lew, Associate Professor, Preston M. Green Department of Electrical & Systems Engineering, McKelvey School of Engineering, Washington University in St. Louis

Researchers can now see the orientation and other minute details in the nanostructures of biological systems that were previously invisible, thanks to a new imaging technology developed by the Lew lab. Their method, known as single-molecule orientation–localization microscopy (SMOLM), visualizes the sheets of peptides beneath Aβ42, a type of A-beta peptide, by using light flashes from chemical probes.

Using SMOLM, they can examine the individual orientation of the underlying beta-sheets to determine how their arrangement connects to the general structure of the amyloid protein.

Multiple Ways to Remodel

Since Aβ42 exhibits erratic behavior, the first step is to attempt to identify a model or pattern of action that can be used to predict the protein's behavior.

The Lew lab discovered some surprises concealed in the amyloid-beta architecture after making some intuitive observations, and now they are able to perform these measurements.

As anticipated, Aβ42 structures that are stable typically maintain stable underlying beta-sheets, whereas structures that are growing have underlying beta-sheets that grow more rigid and defined with time. Beta sheets in decaying structures are progressively less rigid and more disorganized. However, they also discovered multiple ways that A\42 can be updated.

“There are multiple different ways for Aβ42 structures to remain stable, or grow and decay,” said Sun.

Additionally, the researchers found that Aβ42 can behave unexpectedly in terms of growth and decay. Aβ42, for instance, exhibits growth and decay behaviors that maintain the underlying structure. At times, the peptides just pile on top of one another during growth, but the underlying beta-sheet orientations remain unchanged.

In other instances, Aβ42 experiences “stable decay,” in which the opposite occurs—peptides depart, but the beta-sheet structure stays in place.  Lastly, the beta-sheets of Aβ42 occasionally rearrange and shift their orientations without immediately affecting the overall shape. These nanostructural reorganizations may predispose future large-scale remodeling.

“Because SMOLM can track Aβ42’s underlying organization and not just its shape, we can see different kinds of subtypes of remodeling that aren’t visible to diffraction-limited, non-orientation imaging modalities,” said Sun.

If all of this sounds a little hazy, remember that this is only the initial attempt to examine these dynamic nanoscale structures. Sun created this piece while balancing the COVID-19 lockdown restrictions and his three-year undergraduate course load at WashU, which makes it even more noteworthy. It sets the path for him and other researchers to truly understand amyloid architecture.

Sun intends to develop nanoscale imaging systems and sensors that may disclose the underlying mechanisms of diseases that are challenging to treat during the graduate stage of M.D./Ph.D. program.

Sun acknowledges the rigorous training McKelvey Engineering and the Lew lab provided to enable this study and academic trajectory, as well as the MSTP for funding his post-graduation research.

“I’m really glad I went through this journey,” said Sun.