Endorphin-Functional Amyloid with Controlled Fibril Length

The structure of amyloid fibrils is characterised by a flat single-chain form, using a β-type structuring that provides stabilisation mainly by an optimal arrangement of inter-chain hydrogen bonds. An essential feature of amyloid fibrils as a cause of neurodegenerative diseases is their unrestricted propagation as linear fibrils. The identification of the functional amyloid form, which is formed by endorphin, is surprising. The fibril structure of this protein satisfies all the features mentioned except for the feasibility of fibril propagation, limiting its size to a number of chains below 10. A proposed mechanism for the natural termination of fibril size limited to a specific number of chains is discussed in this paper. The characteristics of the endorphin fibril were compared with those of a pathological A-β amyloid. It enables identification of the mechanism present in the structure of the functional amyloid that endorphin forms.