Amyloid beta-protein oligomerization - Prenucleation interactions revealedby photo-induced cross-linking of unmodified proteins

Assembly of the amyloid beta -protein (A beta) into neurotoxic oligomers an d fibrils is a seminal event in Alzheimer's disease. Understanding the earl iest phases of A beta assembly, including prenucleation and nucleation, is essential for the development of rational therapeutic strategies. We have a pplied a powerful new method, photoinduced cross-linking of unmodified prot eins (PI-CUP), to the study of A beta oligomerization. Significant advantag es of this method include an extremely short reaction time, enabling the id entification and quantification of short lived metastable assemblies, and t he fact that no pre facto structural modification of the native peptide is required. Using PICUP, the distribution of A beta oligomers existing prior to assembly was defined. A rapid equilibrium was observed involving monomer , dimer, trimer, and tetramer. A similar distribution was seen in studies o f an unrelated amyloidogenic peptide, whereas nonamyloidogenic peptides yie lded distributions indicative of a lack of monomer preassociation. These re sults suggest that simple nucleation-dependent polymerization models are in sufficient to describe the dynamic equilibria associated with prenucleation phases of A beta assembly.