In a recent study, researchers from the Indian Institute of Technology (IIT), Jodhpur, identified the unique anti-amyloid and chaperone-like activity of a host defence protein, β2-microglobulin, which prevents ⍺-synuclein aggregation. Their research has the potential for developing diagnostic and therapeutic measures for neurodegenerative disorders, such as Parkinson’s disease.
Amyloids are multiprotein aggregates formed due to protein misfolding, and they are associated with several neurodegenerative disorders like Parkinson’s disease, Alzheimer’s disease, and Huntington’s disease. These aggregates are composed of proteins sharing β‑sheet structures. The aggregation of a specific protein, ⍺-synuclein, is linked to Parkinson’s disease. In this disease, ⍺-synuclein aggregates to form Lewy bodies, accumulating inside nerve cells and leading to degeneration of these cells. Consequently, this process results in disease symptoms, including slow movements, tremors, rigidity, and an inability to maintain posture.
β2-microglobulin is a host defence protein present as a receptor on all nucleated cells in the human body. Owing to its β‑sheet structures, this protein can also form amyloids, which deposit in the joints in patients undergoing prolonged dialysis and experiencing renal failure. This deposition leads to a condition called dialysis-related amyloidosis.
β2-microglobulin amyloids are associated with several kidney-related diseases. While studies suggest that patients with end-stage kidney disease face a heightened risk of Parkinson’s, there have been no reported interactions between ⍺-synuclein and β2-microglobulin. Previous research also indicates that other amyloid proteins have anti-amyloid functions under several conditions. In this recent study in the Journal of Molecular Biology, scientists demonstrate how β2-microglobulin monomers can act as a chaperone, interacting with ⍺-synuclein and driving its aggregation along a pathway distinct from that observed in Parkinson’s disease, thereby halting the disease progression.
The authors first used an artificial intelligence-based program, AlphaFold2, to decipher how β 2 ‑microglobulin interacts with α‑synuclein. They found that β‑strand segments (β1 and β2) of α- synuclein, which frequently engage in interactions within amyloid fibrils, interact with the last β‑strand at the C‑terminal of β 2 ‑microglobulin. These β‑strand segments (β1 and β2) of α‑synuclein were not
available for amyloid interactions as they had attained folded structure in the presence of β 2 ‑microglobulin.
Later, they studied this amyloid inhibition via protein-protein interaction using multiple techniques, including crosslinking assays and correlation spectroscopy, in an in vitro setup. Their experiments confirmed that the presence of β2-microglobulin inhibited ⍺-synuclein amyloid formation due to its chaperone-like function (chaperones being proteins assisting in the folding of other proteins). This results in unstructured aggregates that cannot form amyloids again.
The study encountered its own set of hurdles despite its ingenuity. Khushboo Rani, the first author of the study, explained the challenges they faced in understanding the protein-protein interactions responsible for inhibiting amyloid formation and creating stable, non-toxic oligomers.
We worked around this problem by designing an experiment enabling indirect measurement of protein binding. We monitored their diffusion time in a confocal volume through RICS (Raster Image Correlation Spectroscopy).
Rani said, “At first, it was tough to capture images of fluorescent proteins in the solution. Only after trying the procedure a couple of times we could generate reliable data for analysis”.
The team also tested for toxicity of the oligomers resulting from the interaction between β2-microglobulin and ⍺-synuclein in a human neuroblastoma cell line, SHSY-5Y, but found no toxicity. Intrigued by the chaperone-like action of β2-microglobulin, the authors analysed its potential to disrupt preformed ⍺-synuclein amyloids. However, their findings revealed that β2-microglobulin could not disintegrate preformed amyloids.
The findings from this study may guide the future development of potential therapies against Parkinson’s disease targeting a specific region of ⍺-synuclein, which can halt amyloid formation akin to the observed interaction between β2-microglobulin and ⍺-synuclein. Neha Jain, Associate Professor, IIT Jodhpur, and the corresponding author of the study, said,
Our finding provides a lead for the design and development of anti-amyloid drugs as a therapeutic potential to treat amyloid-related neurodegenerative diseases. This will significantly change the dynamics of treatment.
Rani commented on the upcoming research, stating, “Our next step involves understanding the conformation fluctuations in β2-microglobulin and their impact on α‑synuclein amyloid assembly. A detailed understanding of the process will provide us with the opportunity to explore the missing link between systemic kidney-related diseases and increased risk of neurodegenerative diseases”.
Smriti Priya, Senior Scientist, CSIR-Indian Institute of Toxicology Research, Lucknow, who was not associated with the study, said, “The potential clinical relevance of the findings, as evidenced by the increased risk of Parkinson’s disease in patients with end-stage renal disease, adds an important dimension to the study. The use of AlphaFold2 and all-atom MD simulation to model the interaction between β2-microglobulin and ⍺-synuclein provides a cutting-edge approach to understanding protein interactions and their implications in disease pathogenesis. Furthermore, it demonstrates the integration of cutting-edge computational approaches with experimental data, highlighting the interdisciplinary nature of the study, which is crucial for gaining a comprehensive understanding of complex biological processes and disease mechanisms.”