The clue came from a disease endemic to the Fore people in Papua New Guinea, who happened to be occasional cannibals.
It took scientists decades to figure out that infectious misfolded protein aggregates, called prions, were the causal agent responsible for the disease, called Kuru. The specific type of encephalopathy involved in Kuru spread through consumption of human tissues containing the misfolded protein aggregates. Infectious protein aggregates are, of course, not how most communicable diseases spread (often, the nucleic acids (DNA or RNA) in viruses or bacteria are the causal factors).
The symptoms of the disease included uncontrollable shaking, due to the neurotoxic effect of the prion aggregates. Even in popular culture, sometimes cannibalism is associated with loss of motor skills (see "The Book of Eli” starring Denzel Washington). We now know a host of prion diseases — most notably Cruetzfeldt-Jacob disease.
Pathological prion aggregates tend to be rich in a form of protein structure: called beta sheet. Imagine a stack of protein strands that form tape like filaments — that’s what beta-sheet structures look like under electron microscopes. Beta sheets are stabilized by both hydrophobic effect and inter-peptide hydrogen bonds and they can be extremely stable and strong. They show up in super-strong structural proteins such as spider silk and squid suckerin.
Misfolded beta sheet aggregates have been implicated in many neurodegenerative diseases: amyloid beta for Alzheimer’s, polyglutamine for Huntington’s, and alpha-synuclein for Parkinson’s. However, targeting such amyloid aggregates has led to multiple failed clinical trials in recent years.
There is a benign side of beta sheets, which can be useful for the host organism. For example, bacteria such as E. coli use amyloid proteins to build functional fibers called curli. And, in fact, a few researchers have suggested possible positive effects of amyloid proteins against microbial infection. Traditionally, biology and materials science have been treated as two very different subjects but now they're intertwined in a most intriguing way — as research groups around the world build beta sheet based nanofibrous materials as functional biomaterials!
Thus, it’s undoubtedly true that beta sheet protein fibers can be strong functional materials, even if formation of pathological beta sheet aggregates can be disastrous for the host. What doesn't kill you, perhaps, can make you stronger indeed!
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