The Aβ40 and Aβ42 peptides self-assemble into separate homomolecular fibrils in binary mixtures but cross-react during primary nucleation

. Therefore we conclude that fibril-catalysed nucleus formation and elongation are highly sequence specific events but Aβ40 and Aβ42 interact during primary nucleation. These results provide a molecular level description of homomolecular and heteromolecular aggregation steps in mixtures of polypeptide sequence variants.