Extension of the Generic Amyloid Hypothesis to Non-Proteinaceous Metabolite Nano-Assemblies

The formation of ordered amyloid fibrils is associated with several notable human disorders. These nano-scale assemblies are predominantly rich in β-sheet secondary structure and specifically bind dyes, such as ThT and Congo-red. The formation of the amyloid fibrils or earlier pre-fibrillar forms correlates to an apoptotic effect in various tissues. While the formation of these cytotoxic supramolecular entities has previously been linked to proteins and peptides, it was later demonstrated that phenylalanine, as a single amino-acid, can also self-assemble to form amyloid-like fibrils possessing typical ultrastructural, biophysical and biochemical properties. Moreover, it was demonstrated that these phenylalanine assemblies are cytotoxic and antibodies raised against these species deplete fibril toxicity. The generation of antibodies in a phenylketonuria (PKU) mice model and identification of aggregate deposits post mortem in patients` brains suggested a pathological role for these assemblies. To study whether these observations represent a general amyloid-like mechanism prevalent in other metabolic disorders, we have screened metabolites that accumulate in inborn error of metabolism disorders. Here, we reveal that several other metabolites can self-assemble to form ordered amyloid-like ultrastructure in solution with the molecular dimensions and dye-binding specificity similar to canonical amyloid fibrils. In addition, we show that these fibrillar self-assemblies are cytotoxic by the induction of apoptotic programmed cell death, as observed for many amyloid disorders. These results suggest that the formation of nano-scale amyloid-like self-assemblies by metabolites indicate to a general phenomenon of amyloid formation beyond proteins and peptides and offer a new paradigm for metabolic diseases. This may lead to new therapeutic directions of treatments for these disorders beyond a highly-restrictive diet.