Kinetic Modeling and Determination of Reaction Constants of Alzheimer's β-Amyloid Fibril Extension and Dissociation Using Surface Plasmon Resonance

Abstract

To establish the kinetic model of the extension and dissociation of beta-amyloid fibrils (f(A)beta) in vitro, we analyzed these reactions using a surface plasmon resonance (SPR) biosensor. Sonicated f(A)beta were immobilized on the surface of the SPR sensor chip as seeds. The SPR signal increased linearly as a function of time after amyloid beta-peptides (Abeta) were injected into the f(A)beta-immobilized chips. The extension of f(A)beta was confirmed by atomic force microscopy. When flow cells were washed with running buffer, the SPR signal decreased with time after the extension reaction. The curve fitting resolved the dissociation reaction into the fast exponential and slow linear decay phases. Kinetic analysis of the effect of Abeta/f(A)beta concentrations on the reaction rate indicated that both the extension reaction and the slow linear phase of the dissociation were consistent with a first-order kinetic model; i.e., the extension/dissociation reactions proceed via consecutive association/dissociation of Abeta onto/from the end of existing fibrils. On the basis of this model, the critical monomer concentration ([M](e)) and the equilibrium association constant (K) were calculated, for the first time, to be 20 nM and 5 x 10(7) M(-1), respectively. Alternatively, [M](e) was directly measured as 200 nM, which may represent the equilibrium between the extension reaction and the fast phase of the dissociation. The SPR biosensor is a useful quantitative tool for the kinetic and thermodynamic study of the molecular mechanisms of f9A)beta formation in vitro.

Non-steroidal anti-inflammatory drugs have anti-amyloidogenic effects for Alzheimer's β-amyloid fibrils in vitro

“…2E, at a constant fAß(1-40) concentration, a good linearity was observed between the Aß(1-40) concentration and the initial rate of fAß(1-40) extension both in the presence and absence of Ibu. This linearity is again consistent with a first-order kinetic model and indicates that at each Aß(1-40) concentration, the net rate of fAß(1-40) extension is the sum of the rates of polymerization and depolymerization (Naiki and Nakakuki, 1996;Hasegawa et al, 2002). In the presence of 10 µΜ Ibu, the slope of the straight line decreased to about 36%.…”

“…2E, the extension of fAß(1-40) followed a first-order kinetic model even in the presence of Ibu. The net rate of fAß(1-40) extension is the sum of the rates of polymerization and depolymerization (Naiki and Nakakuki, 1996;Hasegawa et al, 2002). Thus, one possible explanation for the finding in Fig.…”

Pressure effects on α-synuclein amyloid fibrils: An experimental investigation on their dissociation and reversible nature

“…The dissociation constants are reported in Table 2 in units of s −1 , in order to be easily compared to literature. In particular, our resulting constants are of the same size of those derived by Hasegawa et al [69] for dissociation of amyloid-β fibrils. Results relative to WT and A30P kinetics show that the kinetic constants k dis increase with pressure.…”

Aβ and tau form soluble complexes that may promote self aggregation of both into the insoluble forms observed in Alzheimer’s disease

“…Surface plasmon resonance is a technique for quantitating protein-protein interaction (8,9). Experiments were performed by using a Biacore 3000 instrument, and results were analyzed with the BIAEVALUTION 4.1 software (Biacore International AB, Uppsala, Sweden).…”