Polyamino acids take amyloid form

The folding of a polypeptide is a tug-of-war with bonds within the main chain fighting against interactions between the side chains, according to new results from Marcus Fändrich (IMB, Jena, Germany) and Christopher Dobson (University of Cambridge, Cambridge, UK). The winner determines whether a polypeptide forms a well-behaved globular structure or the dangerous amyloid fibrils that are associated with diseases such as Alzheimer's or Parkinson's.

Protein folding depends on specific side–chain interactions, but the new results show that amyloid formation does not. The authors examined polyamino acids (PAAs), peptide repeats of one amino acid that cannot fold into globular structures. Repeats of lysine, glutamine, and other amino acids were, however, able to form fibers with the distinctive cross-β structure of amyloids. “Proteins are defined by the sequence of their side chains,” says Fändrich. “PAAs...