Henry J. Heinz claimed to have 57 varieties of pickles in 1896, but Cell [ vol. 184 pp. 4857 – 4873 ’21 ] Page 4862 claims that 24 amyloid polymorphs of alpha-synuclein have been found and structurally characterized.
What does this actually mean in English? The previous 3 articles in this series have discussed the structure of amyloid — the most relevant being https://luysii.wordpress.com/2021/10/11/amyloid-structure-at-last/
Basically, in amyloid some of the protein backbone flattens out so it lies in a single plane, and thousands of the planes stack on top of each other producing the amyloid fiber. In the case of alpha-synuclein some 56 of the 144 amino acids comprising the protein flatten out. Just as throwing a chain with 56 links on the floor will give different conformations of the chain, the conformation of alpha-synuclein is different in each of the polymorphs.
So what?
Well, different polymorphs of another protein, the tau protein which forms the neurofibrillary tangle in Alzheimer’s give rise to at least 25 clinically distinct neurological diseases called tauopathies (3 more are chronic traumatic encephalopathy, corticobasal degeneration, and Pick’s disease). In each of the these four diseases, a different conformation of tau is seen.
Then Nature [ vol. 598, pp. 359 – 363 ’21] blows the field wide open, finding 19 different conformations of tau in clinically distinct diseases. Each clinical disease appears to be associated with a distinct polymorphism. This is also true for the polymorphisms of alpha-synuclein, with distinct conformations being seen in each of Parkinsonism, multiple system atrophy and Lewy body dementia.
In none of the above diseases is there a mutation (change in amino acid sequence) in the protein
Back to alpha-synuclein. How did they get the 24 different conformations? They incubated the protein under different conditions (e.g. different salt concentrations, different alpha-synuclein concentrations, different salts).
Why is this incredibly good news?
Because it moves us past amyloid itself, to the conditions which cause amyloid to form. Certainly, removing amyloid or attacking it hasn’t resulted in any clinical benefit for the Alzheimer patient despite billions being spent by Big Pharma to do so.
We will start to study the ‘root causes’ of amyloid formation. The amino acid sequence of each protein is identical despite the different conformations of the chain in the amyloid. Clearly the causes must be different for each of the different polymorphs of the protein. This just has to be true.
Some cynic said that people who talk about the root causes of crime never get their hands dirty. Hopefully neuroscience is about to take off its gloves.
This is why alternative approaches to Alzheimer’s disease, such as Cassava Biosciences manipulation of filamin A, might bear fruit. For details please see — https://luysii.wordpress.com/2021/03/25/the-science-behind-cassava-sciences-sava/
Just got this back from one of the authors of the Nature paper
“Yes, studying the conditions that lead to all these different structures
is certainly high on our to-do list now.”
Chemiotics II 