Researchers are using microscopy to analyze the structure of amyloid beta proteins, shedding light on their role in neurodegenerative diseases.
Amyloid-beta (A-beta) proteins are protein clusters commonly associated with conditions like Alzheimer’s disease. Despite being widely studied, the exact mechanisms of how these proteins form and disintegrate have remained unclear.
“Understanding how amyloid-beta behaves in various environments, especially in the human brain, has been a challenge,” explained Brian Sun, a former Washington University in St. Louis engineering student now pursuing an MD/PhD degree.
“There are gaps in our understanding of the growth and breakdown processes of these proteins,” he added.
Recent research led by Sun and his colleagues in Associate Professor Matthew Lew’s lab at the Preston M. Green Department of Electrical and Systems Engineering (ESE) in WashU’s McKelvey School of Engineering aims to address this issue.
In a unique study, Sun and his team were able to observe the changes in the underlying structure of amyloid fibril beta-sheet assemblies, which form the foundation of these proteins, in real-time. Previous microscopy studies provided only static images.
“We focused on examining the dynamics of the core structure of A-beta, which could drive the observed changes, rather than just the overall shape variations,” Sun explained.
Lew used the analogy of Lego bricks to illustrate this concept, highlighting that current imaging technologies reveal the complete Lego building but not the organization of individual bricks.
“The individual proteins are always adapting to their surroundings,” Lew stated. “Certain ‘Lego bricks’ influence others to change their shape. The evolving structure of these proteins and their aggregates contributes to the complexity of neurodegenerative diseases.”
The Lew lab developed a novel imaging technique, single-molecule orientation-localization microscopy (SMOLM), enabling them to visualize the orientation and intricate details of biological nanostructures that were previously invisible. By leveraging chemical probes that emit light flashes, they could observe the peptide sheets supporting Aβ42, a specific type of A-beta peptide.
SMOLM allows them to analyze the orientation of individual beta-sheets to explore the correlation between their arrangement and the overall amyloid protein structure.
Various Modes of Transformation
Aβ42 proteins undergo constant transformations, prompting researchers to seek a predictive model to understand this behavior.
With the ability to make these precise measurements, the Lew lab made insightful observations and uncovered unexpected findings within the amyloid-beta structure.
While stable Aβ42 structures typically maintain steady underlying beta-sheets during growth, the beta-sheets in expanding structures become more defined and rigid. Conversely, decaying structures display increasingly disordered and flexible beta-sheets. However, the researchers identified multiple pathways through which Aβ42 can evolve.
“There are diverse mechanisms through which Aβ42 structures can stay stable, grow, or deteriorate,” Sun remarked.
The team also noted that Aβ42 can undergo growth and decay in unexpected ways. For instance, the protein may grow or decay while retaining the underlying structure, with peptides accumulating or dispersing while the beta-sheet orientation remains constant. In other instances, the protein undergoes “stable decay,” where peptides depart while the beta-sheet structure remains intact. Additionally, beta-sheets might reorganize without an immediate change in the protein’s overall shape, potentially setting the stage for future substantial transformations.
“By tracking the underlying organization of Aβ42 with SMOLM, we can discern various subtypes of transformations not visible using traditional imaging methods,” Sun explained.
Given the intricate nature of these constantly shifting nanostructures, this initial study is paving the way for a deeper understanding of amyloid architecture. Sun, who navigated through COVID-19 challenges and an intensive undergraduate curriculum at WashU, is poised to delve further into these inquiries as he progresses through his MD/PhD program, where he aims to develop imaging systems and sensors that can uncover the hidden mechanisms of complex diseases.
He credits WashU’s ESE department and the Lew lab for providing the training that enabled this study and his academic journey, as well as WashU’s MSTP program for supporting his ongoing research post-graduation. “I’m grateful for the opportunities that led me to this point,” he expressed.
This research received funding from the National Institute of General Medical Sciences of the National Institutes of Health under Award Number R35GM124858.
