prionoid

Prionoid is a term used in molecular biology to describe proteins or protein-based elements that display prion-like properties, notably the ability to adopt an alternative conformational state that templates its own propagation and induces heritable phenotypic changes in cells. Unlike bona fide prions, which are infectious between individuals, prionoids may propagate within a cell or lineage without clear evidence of inter-host transmission.

Mechanistically, prionoids typically form amyloid or beta-sheet–rich aggregates that recruit soluble protein and convert it into the prion form. Propagation is often aided by cellular chaperones and can produce heritable traits during cell division. In yeast, well-characterized prion elements such as [PSI+] and [URE3] are often described as prion-like elements or prionoids, illustrating epigenetic-like inheritance without outside infection. In mammals, several proteins with prion-like domains, including RNA-binding proteins with low-complexity regions, can form self-templating aggregates; these are discussed as prionoids when they demonstrate prion-like propagation, though their role in infectious disease remains debated.

Prionoids are studied to understand normal cellular regulation and the potential role of prion-like propagation in development and disease, including neurodegenerative conditions in which protein aggregation is implicated. The term is not universally standardized and is used variably; some researchers reserve “prionoid” for non-infectious or cell-to-cell propagating amyloids, while others apply it more broadly to any prion-like, self-templating protein.