The body manufactures proteins by chaining together smaller molecules called amino acids. Once the amino acids are chained together, they fold into complex three-dimensional shapes. How a protein folds determines what a protein does.
In the 1950s, Nobel laureate Linus Pauling figured out that for most proteins, there are two preferred basic shapes:
- An alpha helix, where the protein folds into a right-handed spiral coil; and
- A beta sheet configuration, like a stack of folded cardboard panels.
Chris Dobson, the head of Cambridge’s chemistry department, is one of the world’s leading experts on proteins. He found that proteins don’t always fold up correctly into their native state. Using chemical agents and heat energy, Dobson showed that it was easy to unfold protein molecules. And once unfolded, the misfolded molecules can morph into long, thin “fibrils” that stick together and grow into clumps, or amyloids, which over time could lead to amyloid diseases.
Such amyloids almost never build up in healthy living cells because the cells have control systems to prevent molecules from misfolding. But these cellular controls can fail for multiple reasons such as genes, environment, and age. Even though each disease involves a different protein – alpha-synuclein is involved with PD, tau and amyloid-beta with Alzheimer’s, and huntingtin with Huntinton’s disease – the cellular control systems fail in much the same way.
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In 1972, a physician named Stanley Prusiner watched one of his patients die of a rare condition called Creutzfeldt-Jakob disease. In this rapidly progressing disease, patients suffer dementia, memory loss, and hallucinations. He discovered that this disease had linked to two other infectious neurodegenerative disease: scrapie – a disease that affects sheep and goats with a kind of animal dementia; and kuru – a disease of the Fore tribe in New Guinea. Prusiner noted that the three diseases had much in common. All were 100 percent fatal. All left sponge-like holes in their victims’ brains. All killed without evoking an immune response. All required long incubation times – generally measured in years. All appeared to be contagious; when brain tissue from deceased sheep or people was injected into healthy animals, the recipients got sick.
In the 1980s and 1990s, scientists found four other diseases that behaved like scrapie, kuru, and Credtzfeldt-Jakob disease: bovine spongiform encephalopathy (BSE), or mad cow disease; a new variant of Creutzfeldt-Jakob disease resulting from eating BSE-diseased cattle (vCJD), something that had caused a massive public health scare in Britain; and two very rare hereditary diseases, fatal familial insomnia and Gerstmann-Sträussler-Scheinker disease.
But most remarkable was that this set of diseases appeared to be carried by a pathogen unlike anything seen in the history of medicine. The mysterious entity was very difficult to kill. Scrapie brain tissue, for example, remained infectious even after being frozen, boiled in water, soaked in formaldehyde, exposed to ionizing radiation, and flooded with intense ultraviolet light- processes that were known to rapidly destroy the DNA and RNA inside pathogens like viruses and bacteria.
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Prusiner spend years trying to isolate the infectious agent. He found no virus. He claimed that the disease was directly spread by proteins – not just any proteins, but infectious ones, which he called prions. In 1997, Prusiner received the Nobel Prize for “discovery” of prions.
Something similar seems to happen with all amyloid diseases: misfolded single proteins (monomers) stick to other molecules to form oligomers, which grow into fibrils, which become amyloid plaques. Along the way, growing fibril structures can break off and serve as templates for secondary amyloid growth. The secondary spread of fibrils is quicker in pure prion diseases like scrapie; that’s what may account for prion diseases’ animal-to-animal contagiousness. But the idea is the same for noncontagious diseases like PD. And compelling evidence that alpha-synuclein could spread in a prion-like manner in fact emerged in 2007, data that persuaded neuroscientists and chemist.
In 2007, by performing autopsies of neural grafting patients, Swedish scientist Patrik Brundin and the neuropathologist Jeff Kordower came up with two conclusion. First, the fetal transplants did not stop the progression of the disease; even after the transplanting of the new cells, the disease process continued. Second, the misfolded alpha-synuclein was truly capable of jumping from cell to cell in a prion-like fashion. Given time, the misfolded protein could spread throughout the brain. This was somewhat of a paradigm shift, and a new era in PD research started.
Dobson believes these protein-folding disease will be easier to cure than cancer. To slow down Alzheimer’s and PD, you need to reduce the amount of beta amyloid and alpha-synuclein. One compound named Anle138b has proved effective in mouse models of PD. It crossed the blood-brain barrier, caused no adverse effects at high doses, and significantly reduced oligomer accumulation. As a result, Anle138b-treated parksinsonian mice experience less nerve call degeneration and survived much longer than untreated controls.
- Misfolded proteins can morph into an amyloid form leading to amyloid diseases such as PD, Alzheimer’s, and Huntingon’s disease.
- Stanley Prusiner discovered prion, an infectious agent composed entirely of protein material, that can fold in multiple ways, leading to disease similar to viral infection.
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