A new scientific report reveals that the protein aggregates associated with Parkinson’s disease are not inert clumps of cellular waste, but rather are chemically active structures that can systematically destroy the primary energy molecule used by brain cells. The research, published in the journal Advanced Science, demonstrates that these protein plaques can function like tiny, rogue enzymes, breaking down adenosine triphosphate and potentially starving neurons of the power they need to survive and function.
Scientists have long sought to understand how the accumulation of protein clumps, known as amyloids, leads to the devastating neuronal death seen in neurodegenerative conditions like Parkinson’s disease. These clumps are primarily made of a misfolded protein called alpha-synuclein.
The prevailing view has been that these aggregates cause harm by physically disrupting cellular processes, poking holes in membranes, or sequestering other important proteins. However, a team of researchers led by Pernilla Wittung-Stafshede at Rice University suspected there might be more to the story.
Previous work from the same group had shown that alpha-synuclein amyloids were not chemically inactive. They could facilitate certain chemical reactions on simple model compounds in a test tube. This led the researchers to question if these amyloids could also act on biologically significant molecules inside a cell. They focused on one of the most fundamental molecules in all of life: adenosine triphosphate, the universal energy currency that powers nearly every cellular activity.
Neurons have exceptionally high energy demands and cannot store fuel, making them particularly vulnerable to any disruption in their adenosine triphosphate supply. The team hypothesized that if amyloids could break down this vital molecule, it would represent a completely new way these pathological structures exert their toxicity.
To investigate this possibility, the scientists conducted a series of experiments. First, they needed to confirm that adenosine triphosphate even interacts with the alpha-synuclein amyloids. They used a chemical reaction they had previously studied, where the amyloids break down a substance called para-nitrophenyl orthophosphate.
When they added adenosine triphosphate to this mixture, the original reaction stopped. This competitive effect suggested that adenosine triphosphate was binding to the same active location on the amyloid surface, pushing the other substance out of the way.
Having established that adenosine triphosphate binds to the amyloids, the researchers then tested whether it was being broken down. They mixed prepared alpha-synuclein amyloids with a solution of adenosine triphosphate and used a diagnostic tool called the Malachite Green assay, which changes color in the presence of free phosphate, a byproduct of adenosine triphosphate breakdown.
They observed a steady increase in free phosphate over time, confirming that the amyloids were indeed cleaving the phosphate bonds in adenosine triphosphate. This activity was catalytic, meaning a single amyloid structure could process many molecules of adenosine triphosphate, one after another. The same experiment performed with individual, non-clumped alpha-synuclein proteins showed no such effect, indicating this energy-draining ability is a feature specific to the aggregated, amyloid form.
To understand the mechanism behind this chemical activity, the team used a powerful imaging technique known as cryogenic electron microscopy. This method allowed them to visualize the structure of the alpha-synuclein amyloid at a near-atomic level of detail while it was bound to adenosine triphosphate.
The resulting images revealed a remarkable transformation. The amyloid itself was formed from two intertwined filaments, creating a cavity between them. When adenosine triphosphate entered this cavity, a normally flexible and disordered segment of the alpha-synuclein protein, consisting of amino acids 16 through 22, folded into an ordered beta-strand. This newly formed structure acted like a lid, closing over the cavity and trapping the adenosine triphosphate molecule inside.
This enclosed pocket was lined with several positively charged amino acids called lysines. Since the phosphate tail of adenosine triphosphate is strongly negatively charged, these lysines likely serve to attract and hold the energy molecule in a specific orientation. The structure suggested that this induced-fit mechanism, where the amyloid changes its shape upon binding its target, was a key part of its chemical function.
To prove that these specific lysine residues were responsible for the activity, the researchers genetically engineered several mutant versions of the alpha-synuclein protein. In each version, they replaced one or more of the key lysines in the cavity with a neutral amino acid, alanine. These mutant proteins were still able to form amyloid clumps that looked similar to the original ones.
When they tested the mutant amyloids for their ability to break down adenosine triphosphate, they found the activity was almost completely gone. This result confirmed that the positively charged lysines are essential for the amyloid’s ability to perform the chemical reaction.
In a final step, the scientists solved the high-resolution structure of one of the inactive mutant amyloids (K21A) while it was bound to adenosine triphosphate. The images showed that the energy molecule could still sit in the cavity, but its orientation was different from that seen in the active, non-mutant amyloid.
More importantly, in this inactive complex, the flexible protein segment did not fold over to form the enclosing lid. This finding provided strong evidence that both the proper positioning of adenosine triphosphate by the lysines and the structural rearrangement that closes the cavity are necessary for the breakdown to occur.
The study does have some limitations. The experiments were conducted in a controlled laboratory setting, not in living cells or organisms. The specific structural form of the alpha-synuclein amyloid studied, known as polymorph type 1A, has not yet been identified in the brains of Parkinson’s patients, although similar structures exist.
Also, the rate at which the amyloids broke down adenosine triphosphate was slow compared to natural enzymes. Future research will need to determine if this process occurs within the complex environment of a neuron and if other, more clinically relevant amyloid forms share this toxic capability.
Despite these caveats, the findings introduce a new and potentially significant mechanism of neurodegeneration. The researchers suggest that even a slow reaction could have a profound local effect. An amyloid plaque contains a very high density of these active sites. This could create a zone of severe energy depletion in the immediate vicinity of the plaque, disabling essential cellular machinery.
For instance, cells use chaperone proteins that require adenosine triphosphate to try to break up these very amyloids. If the chaperones approach an amyloid plaque and enter an energy-depleted zone, their rescue function could be disabled, effectively allowing the plaque to protect itself and persist. This work transforms the view of amyloids from passive obstacles into active metabolic drains, opening new avenues for understanding and potentially treating Parkinson’s disease.
The study, “ATP Hydrolysis by α-Synuclein Amyloids is Mediated by Enclosing β-Strand,” was authored by Lukas Frey, Fiamma Ayelen Buratti, Istvan Horvath, Shraddha Parate, Ranjeet Kumar, Roland Riek, and Pernilla Wittung-Stafshede.
