The many faces of amyloid: Protein misfolding: failure or function?

The ability of proteins to recognize, bind and manipulate a wide range of other molecules lies at the heart of virtually every cellular process. In order to achieve this, proteins must fold into a precise three-dimensional structure. A failure to achieve this structure, and the associated loss of protein stability and function, results in diseases such as muscular dystrophy and cystic fibrosis. In addition, the misfolding and aggregation of proteins to form fibrillar species is associated with the progression of amyloid diseases such as Alzheimer's and Huntington's and prion diseases including Creutzfeldt– Jakob disease and bovine spongiform encephalopathy (BSE, or ‘mad cow disease’). In this article, we consider advances in the study of protein folding and misfolding and their relevance to biological function. We also explore the issue of protein ‘misfolding’ to form functional aggregated structures, such as the mode of epigenetic inheritance mediated by fungal prions and the formation of amyloid fibrils with positive biological functions in bacteria.