ABSTRACT:
Morris2009 - α-Synuclein aggregation
variable temperature and pH
This model is described in the article:
Alpha-synuclein aggregation
variable temperature and variable pH kinetic data: a
re-analysis using the Finke-Watzky 2-step model of nucleation
and autocatalytic growth.
Morris AM, Finke RG.
Biophys. Chem. 2009 Mar; 140(1-3):
9-15
Abstract:
The aggregation of proteins is believed to be intimately
connected to many neurodegenerative disorders. We recently
reported an "Ockham's razor"/minimalistic approach to analyze
the kinetic data of protein aggregation using the Finke-Watzky
(F-W) 2-step model of nucleation (A-->B, rate constant k(1))
and autocatalytic growth (A+B-->2B, rate constant k(2)).
With that kinetic model we have analyzed 41 representative
protein aggregation data sets in two recent publications,
including amyloid beta, alpha-synuclein, polyglutamine, and
prion proteins (Morris, A. M., et al. (2008) Biochemistry 47,
2413-2427; Watzky, M. A., et al. (2008) Biochemistry 47,
10790-10800). Herein we use the F-W model to reanalyze protein
aggregation kinetic data obtained under the experimental
conditions of variable temperature or pH 2.0 to 8.5. We provide
the average nucleation (k(1)) and growth (k(2)) rate constants
and correlations with variable temperature or varying pH for
the protein alpha-synuclein. From the variable temperature
data, activation parameters DeltaG(double dagger),
DeltaH(double dagger), and DeltaS(double dagger) are provided
for nucleation and growth, and those values are compared to the
available parameters reported in the previous literature
determined using an empirical method. Our activation parameters
suggest that nucleation and growth are energetically similar
for alpha-synuclein aggregation (DeltaG(double
dagger)(nucleation)=23(3) kcal/mol; DeltaG(double
dagger)(growth)=22(1) kcal/mol at 37 degrees C). From the
variable pH data, the F-W analyses show a maximal k(1) value at
pH approximately 3, as well as minimal k(1) near the
isoelectric point (pI) of alpha-synuclein. Since solubility and
net charge are minimized at the pI, either or both of these
factors may be important in determining the kinetics of the
nucleation step. On the other hand, the k(2) values increase
with decreasing pH (i.e., do not appear to have a minimum or
maximum near the pI) which, when combined with the k(1) vs. pH
(and pI) data, suggest that solubility and charge are less
important factors for growth, and that charge is important in
the k(1), nucleation step of alpha-synuclein. The chemically
well-defined nucleation (k(1)) rate constants obtained from the
F-W analysis are, as expected, different than the 1/lag-time
empirical constants previously obtained. However, k(2)x[A](0)
(where k(2) is the rate constant for autocatalytic growth and
[A](0) is the initial protein concentration) is related to the
empirical constant, k(app) obtained previously. Overall, the
average nucleation and average growth rate constants for
alpha-synuclein aggregation as a function of pH and variable
temperature have been quantitated. Those values support the
previously suggested formation of a partially folded
intermediate that promotes aggregation under high temperature
or acidic conditions.
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