Kamihira2000 - calcitonin fibrillation kinetics

Kamihira2000 - calcitonin fibrillation kinetics

This model studies the kinetics of human calcitonin fibrillation described as a two-step process. Empirical data is used to determine the parameter values. Results show that the first step in fibrillation is a slow homogenous reaction and the second step is a fast autocatalytic heterogenous reaction.

This model is described in the article:

Conformational transitions
and fibrillation mechanism of human calcitonin as studied by
high-resolution solid-state 13C NMR.

Kamihira M, Naito A, Tuzi S, Nosaka
AY, Saitô H.
Protein Sci. 2000 May; 9(5):
867-877
Abstract:

Conformational transitions of human calcitonin (hCT) during
fibril formation in the acidic and neutral conditions were
investigated by high-resolution solid-state 13C NMR
spectroscopy. In aqueous acetic acid solution (pH 3.3), a local
alpha-helical form is present around Gly10 whereas a random
coil form is dominant as viewed from Phe22, Ala26, and Ala31 in
the monomer form on the basis of the 13C chemical shifts. On
the other hand, a local beta-sheet form as viewed from Gly10
and Phe22, and both beta-sheet and random coil as viewed from
Ala26 and Ala31 were detected in the fibril at pH 3.3. The
results indicate that conformational transitions from
alpha-helix to beta-sheet, and from random coil to beta-sheet
forms occurred in the central and C-terminus regions,
respectively, during the fibril formation. The increased 13C
resonance intensities of fibrils after a certain delay time
suggests that the fibrillation can be explained by a two-step
reaction mechanism in which the first step is a homogeneous
association to form a nucleus, and the second step is an
autocatalytic heterogeneous fibrillation. In contrast to the
fibril at pH 3.3, the fibril at pH 7.5 formed a local
beta-sheet conformation at the central region and exhibited a
random coil at the C-terminus region. Not only a hydrophobic
interaction among the amphiphilic alpha-helices, but also an
electrostatic interaction between charged side chains can play
an important role for the fibril formation at pH 7.5 and 3.3
acting as electrostatically favorable and unfavorable
interactions, respectively. These results suggest that hCT
fibrils are formed by stacking antiparallel beta-sheets at pH
7.5 and a mixture of antiparallel and parallel beta-sheets at
pH 3.3.

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