Tag Archives: Protein Misfolding Cyclic Amplification

The prion battles continue with a historical note at the end

Now that we know proteins don’t have just one shape, and that 30% of them have unstructured parts, it’s hard to remember just how radical that Prusiner’s proposal that a particular conformation (PrPSc) of the normal prion protein (PrPC) caused other prion proteins to adopt it and cause disease was back in the 80s. Actually Kurt Vonnegut got there first with Ice-9 in “Cat’s Cradle ” in 1963. If you’ve never read it, do so, you’ll like it.

There was huge resistance to Prusiner’s idea, but eventually it became accepted except by Laura Manuelidis (about which more later). People kept saying the true infectious agent was a contaminant in the preparations Prusiner used to infect mice and that the prion protein (called PrPC) was irrelevant.

The convincing argument that Prusiner was right (for me at least) was PMCA (Protein Misfolding Cyclic Amplification) in which you start with a seed of PrPSc (the misfolded form of the normal prion protein PrPC), incubate it with a 10,000 fold excess of normal PrPC, which is converted by the evil PrPSC to more of itself. Then you sonicate what you’ve got breaking it into small fragments, and continue the process with another 10,000 fold excess of normal PrPC. Repeat this 20 times. This should certainly dilute out any infectious agent along for the ride (no living tissue is involved at any point). You still get PrPSc at the end. For details see Cell vol. 121 pp. 195 – 206 ’05.

Now comes [ Proc. Natl. Acad. Sci. vol. 117 pp. 23815 – 23822 ’20 ] which claims to be able to separate the infectivity of prions from their toxicity. Highly purified mouse prions show no signs of toxicity (neurite fragmentation, dendritic spine density changes) in cell culture, but are still infectious producing disease when injected into another mouse brain.

Even worse treatment of brain homogenates from prion infected mice with sodium laroylsarcosine destroys the toxicity to cultured neurons without reducing infectivity to the next mouse.

So if this paper can be replicated it implies that the prion protein triggers some reaction in the intact brain which then kills the animals.

Manuelidis thought in 2011 that the prion protein is a reaction to infection, and that we haven’t found the culprit. I think the PCMA pretty much destroyed that idea.

So basically we’re almost back to square one with what causes prion disease. Just to keep you thinking. Consider this. We can knock out the prion protein gene in mice. Guess what? The mice are normal. However, injection of the abnormal prion protein (PrPSc) into their brains (which is what researchers do to transmit the disease) doesn’t cause any disease.

Historical notes: I could have gone to Yale Med when Manuelidis was there, but chose Penn instead. According to Science vol. 332 pp. 1024 – 1027 ’11 she was one of 6 women in the class, and married her professor (Manuelidis) aged 48 when she was 24 graduating in 1967. In today’s rather Victorian standards of consent, power differential between teacher and student, that would probably have gotten both of them bounced out.

So I went to Penn Med. graduating in ’66. Prusiner graduated in ’68. He and I were in the same medical fraternity (Nu Sigma Nu). Don’t think animal house, medical fraternities were a place to get some decent food, play a piano shaped object and very occasionally party. It’s very likely that we shared a meal, but I have no recollection.

Graduating along with me was another Nobel Laureate to be — Mike Brown, he of the statins. Obviously a smart guy, but he didn’t seem outrageously smarter than the rest of us.