Islet amyloid: Phase partitioning and secondary nucleation are central to the mechanism of fibrillogenesis

Shae B. Padrick, Andrew D. Miranker

Research output: Contribution to journalArticle

249 Citations (Scopus)

Abstract

Islet amyloid polypeptide (IAPP) contributes to the pathogenesis of type II diabetes by depositing as cytotoxic amyloid fibers in the endocrine pancreas. Fiber formation occurs with a marked conformational change from an unstructured precursor. Using real-time quantitative kinetic methods, fibrillogenesis was characterized as a function of protein, denaturant, and seed concentration. Several observations are in sharp contrast to the expectations for nucleation-dependent polymerization. First, the half-time of conversion for both de novo and seeded kinetics were found to be independent of protein concentration. Second, while elongation kinetics scale linearly with protein concentration, they are relatively insensitive to changes in the total seed concentration. Third, seeded bypass of de novo fiber formation kinetics shows a lag phase. The seeded lag phase is eliminated by a time delay before the introduction of seed to a de novo reaction. Last, conversion is highly cooperative, with the time required for 10-90% conversion occurring much faster than the lag time. At a minimum, four kinetic steps are required to describe these observations: activation, fiber independent nucleation, fiber-dependent nucleation, and elongation. Furthermore, we invoke a phase transition in which protein initially forms an off-pathway dispersion. This single construct allows us to model both the concentration independence of the de novo reaction time and the first-order concentration dependence of the elongation kinetics. Marked acceleration of this reaction by hexafiuoro-2-propanol reinforces this view by altering the relative solubility of the two phases and/or by stabilizing hydrogen-bonded structures in the transition states of the reaction pathway.

Original languageEnglish (US)
Pages (from-to)4694-4703
Number of pages10
JournalBiochemistry
Volume41
Issue number14
DOIs
StatePublished - Apr 9 2002

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Amyloid
Nucleation
Kinetics
Fibers
Seed
Elongation
Seeds
Proteins
Islet Amyloid Polypeptide
2-Propanol
Phase Transition
Medical problems
Islets of Langerhans
Polymerization
Solubility
Type 2 Diabetes Mellitus
Hydrogen
Time delay
Phase transitions
Chemical activation

ASJC Scopus subject areas

  • Biochemistry

Cite this

Islet amyloid : Phase partitioning and secondary nucleation are central to the mechanism of fibrillogenesis. / Padrick, Shae B.; Miranker, Andrew D.

In: Biochemistry, Vol. 41, No. 14, 09.04.2002, p. 4694-4703.

Research output: Contribution to journalArticle

Padrick, Shae B. ; Miranker, Andrew D. / Islet amyloid : Phase partitioning and secondary nucleation are central to the mechanism of fibrillogenesis. In: Biochemistry. 2002 ; Vol. 41, No. 14. pp. 4694-4703.
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