SpectroscopyNOW- Imaging Parkinson's protein: NMR and EPR

Imaging Parkinson's protein: NMR and EPR

Combined effort

A combined approach using nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy reveals details of the changes that occur in the protein α-synuclein in Parkinson's disease.

The protein α-synuclein is found mainly in the brain, although it also occurs in heart tissue, muscles and elsewhere. It is present mainly at the tips of neurons in the presynaptic terminals. The protein is thought to play a critical role in Parkinson's disease and other neurodegenerative disorders. Science already knows quite a lot about the structure of the protein within the Parkinson's-typical amyloid deposits that apparently give rise to the symptoms of the disease. However, until now nothing was known about the original state of the protein in the healthy cell.

Now, researchers at the Leibniz-Institut für Molekulare Pharmakologie (FMP) in Berlin, Germany, have used NMR and EPR together to visualize for the first time the healthy form of this protein in healthy cells. Paradoxically, it seems to exist in an unstructured state one that might in a different protein under different circumstances be described as misfolded and perhaps itself a cause of disease. The team describes their findings in two papers published in the journal Nature and its sibling publication Nature Communications. It is also now obvious that the structure of this protein changes dramatically through the course of the disease.

Amyloid aggregates

Accumulation of misfolded proteins, so-called amyloid aggregates, are known to be present in the brains of patients with a range of neurodegenerative diseases including Parkinson's, Alzheimer's and Huntington's. Amyloids are essentially any protein fragments made by the body that present in this particular manner and are ultimately responsible for the demise of neurons. The protein α-synuclein is known to be a primary constituent of these amyloid aggregates and so is thought to play a significant role in the development of Parkinson's disease.

The structure of this protein in disease is well known but understanding what it looks like in otherwise healthy cells is important to understanding the pathology and progression of the disease. The NMR and EPR spectra have now given the team an atomic resolution image of the "healthy" form of the protein.

"We discovered the unstructured state that the protein also has in the purified state," explains biophysicist Philipp Selenko, Head of the In-cell NMR Spectroscopy research group. "This is actually rather surprising, because it was inconceivable up to now that such an unstructured state can survive at all in a cellular milieu."

It seems from the insights revealed in the Nature paper that a specific region -the NAC region - of this protein protects healthy cells from penetration by foreign molecules. However, this central region also plays an important part in the formation of highly structured amyloid aggregates. Why the protective properties of the protein are lost in neurodegenerative diseases is one of the key questions that researchers hope one day to be able to answer. "In the diseased state, this protein must change structurally to such an extent that the NAC region becomes accessible for other molecules, so that these regions can accumulate, start to grow and thus form the amyloid structures," Selenko suspects.

Research might now build on these new findings. The Berlin team is for instance already planning to generate artificially aged cells in the laboratory and to introduce the amyloid protein into them and see what impact that has on the spectra. Parkinson's and other neurodegenerative diseases are generally age-related diseases, except in certain inherited early-onset forms and other special cases. Ultimately, the researchers want to home in on the cellular state that corresponds to the beginnings of the disease. "We hope to watch the protein as the protection of the NAC region is gradually lost and how it begins to form amyloid-like structures," explains Selenko.

Repairing neurodegeneration

In the second paper, the team reported on the effects of their deliberately damaging the protein at particular points along its amino acid chain to again mimic the effects of age. When these damaged proteins were introduced into young, healthy cells, the team could study how cell repair processes could reverse the damage in some regions but not in others. The irreparable region was the one most critical to the protein's functionality. The team now plans to investigate what causes the repair mechanisms to fail and to see whether that is the underlying problem that leads to neurodegenerative processes.