Direct conversion of an oligopeptide from a beta-sheet to an alpha-helix: a model for amyloid formation.
A 16-amino acid oligopeptide forms a stable beta-sheet structure in water. In physiological solutions it is able to self-assemble to form a macroscopic matrix that stains with Congo red. On raising the temperature of the aqueous solution above 70 degrees C, an abrupt structural transition occurs in the CD spectra from a beta-sheet to a stable alpha-helix without a detectable random-coil intermediate. With cooling, it retained the alpha-helical form and took several weeks at room temperature to partially return to the beta-sheet form. Slow formation of the stable beta-sheet structure thus shows kinetic irreversibility. Such a formation of very stable beta-sheet structures is found in the amyloid of a number of neurological diseases. This oligopeptide could be a model system for studying the protein conformational changes that occurs in scrapie or Alzheimer disease. The abrupt and direct conversion from a beta-sheet to an alpha-helix may also be found in other processes, such as protein folding and protein-protein interaction. Furthermore, such drastic structure changes may also be exploited in biomaterials designed as sensors to detect environmental changes.
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Department of Biology, Center for Biomedical Engineering, Massachusetts Institute of Technology, Cambridge 02139-4307, USA. Shuguang@MIT.EDU
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D000595:Amino Acid Sequence; D000682:Amyloid / Q000737:chemistry*; D000818:Animals; D002942:Circular Dichroism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D009422:Nervous System Diseases / Q000209:etiology; D009842:Oligopeptides / Q000737:chemistry*; D009994:Osmolar Concentration; D017433:Protein Structure, Secondary; D014461:Ultracentrifugation
D000682:Amyloid; D009842:Oligopeptides