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Spectroscopic studies on native and protofibrillar insulin.
1Bioorganic and Neurochemistry Laboratory, Central Leather Research Institute, Adyar, Chennai 600 020, India.
Journal of Structural Biology
|May 4, 2005
Summary
Insulin amyloid fibrils form toxic protofibrils with flexible monomers and a hydrophobic cavity. These structures are stabilized by beta-sheets but can be unfolded by GdnHCl, revealing a "zipping" mechanism.
Area of Science:
- Biochemistry
- Structural Biology
- Biophysics
Background:
- Amyloid fibrils are associated with various diseases.
- The protofibrillar (PF) state is often the most toxic intermediate in amyloid formation.
- Previous studies showed insulin amyloid fibrils adopt a well-folded conformation.
Purpose of the Study:
- To characterize the structural and dynamic properties of insulin protofibrils (PFs).
- To investigate the binding interactions of PFs with ANS.
- To understand the stability and unfolding mechanisms of insulin PFs.
Main Methods:
- Cryoelectron microscopy
- Fluorescence spectroscopy (FRET)
- Chemical denaturation (GdnHCl)
- Solvent-induced conformational changes (TFE)
Main Results:
- Insulin PFs consist of flexible monomers with a hydrophobic cavity capable of binding ANS.
- ANS binding sites are close to insulin tyrosine residues, as shown by FRET.
- PFs exhibit beta-sheet, helical, and turn structures, indicating conformational dynamics.
- PFs can be unfolded by GdnHCl, suggesting a "zipping" assembly, and dissociated by TFE, highlighting the role of beta-sheets.
Conclusions:
- Insulin PFs are dynamic structures with flexible monomers and a distinct hydrophobic cavity.
- The stability of insulin PFs is attributed to beta-sheet structures and a "zipping" mechanism.
- Understanding PF structure and dynamics is crucial for developing therapeutic strategies against amyloid diseases.