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A microbeam X-ray diffraction study of insulin spherulites.
1Japan Synchrotron Radiation Research Institute, SPring-8, Kouto, Sayo, Hyogo 679-5198, Japan. yagi@spring8.or.jp
Journal of Molecular Biology
|August 22, 2006
Summary
Insulin forms amyloid fibrils within spherulites. X-ray fiber diffraction reveals their symmetric growth and beta-sheet structure, proposing a molecular model for these insulin aggregates.
Area of Science:
- Biophysics
- Structural Biology
- Materials Science
Background:
- Insulin can aggregate into spherical structures called spherulites under specific conditions (low pH, high temperature).
- These spherulites are composed of a core and radiating fibrils, hypothesized to be amyloid fibers with beta-sheet structures.
Purpose of the Study:
- To investigate the structural organization of insulin spherulites and their constituent fibrils using advanced X-ray diffraction techniques.
Main Methods:
- X-ray fiber diffraction was employed to analyze insulin spherulites (50-100 micrometers in diameter) using a microbeam (6 micrometers).
- Two-dimensional diffraction patterns were collected and analyzed to determine fibril arrangement and spacing.
Main Results:
- Diffraction patterns exhibited centrosymmetric scatter, indicating symmetric fibril growth.
- Key Bragg spacings were identified: 0.48 nm (along fibrils, indicating beta-strand hydrogen bonds), 1.2 nm (peptide chain arrangement), 3.3 nm (protofilament arrangement), and 23 nm (fibril separation).
Conclusions:
- The study provides detailed structural insights into insulin spherulites and their amyloid fibrils.
- A model for the fibril structure, incorporating the extended insulin molecule, is proposed based on the diffraction data.