AMYLOID BETA-PROTEIN FIBRILLOGENESIS - DETECTION OF A PROTOFIBRILLAR INTERMEDIATE

Fibrillogenesis of the amyloid beta-protein (A beta) is a seminal path ogenetic event in Alzheimer's disease, Inhibiting fibrillogenesis is t hus one approach toward disease therapy, Rational design of fibrilloge nesis inhibitors requires elucidation of the stages and kinetics of A beta fibrillogenesis, We report results of studies designed to examine the initial stages of A beta oligomerization, Size exclusion chromato graphy, quasielastic light scattering spectroscopy, and electron micro scopy were used to characterize fibrillogenesis intermediates, After d issolution in 0.1 M Tris-HCl, pH 7.4, and removal of preexistent seeds , A beta chromatographed almost exclusively as a single peak, The mole cules composing the peak had average hydrodynamic radii of 1.8 +/- 0.2 nm, consistent with the predicted size of dimeric A beta. Over time, an additional peak, with a molecular weight >100,000, appeared, This p eak contained predominantly curved fibrils, 6-8 nm in diameter and <20 0 nm in length, which we have termed ''protofibrils.'' The kinetics of protofibril formation and disappearance are consistent with protofibr ils being intermediates in the evolution of amyloid fibers, Protofibri ls appeared during the polymerization of A beta-(1-40), A beta-(1-42), and A beta-(1-40)-Gln(22), peptides associated with both sporadic and inherited forms of Alzheimer's disease, suggesting that protofibril f ormation may be a general phenomenon in A beta fibrillogenesis. If so, protofibrils could be attractive targets for fibrillogenesis inhibito rs.