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Biophys. J. BioFAST: First Published March 13, 2006. doi:10.1529/biophysj.105.070912
© 2006 by the Biophysical Society.

A more recent version of this article appeared on June 1, 2006.
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PROTEINS

Sulfates dramatically stabilize a salt dependent type of glucagon fibrils

Jesper Søndergaard Pedersen 1, James M Flink 2, Dantcho Dikov 3 and Daniel E. Otzen 4*

1 Department of Life Sciences, Aalborg University, Sohngaardsholmsvej 49, DK-9000 Aalborg
2 Novo Nordisk A/S, Novo Alle, DK-2880 Bagsværd, DENMARK
3 Novo Nordisk A/S, Brogaardsvej 66, DK-2820 Gentofte, DENMARK
4 Aalborg University

* To whom correspondence should be addressed. E-mail: dao{at}bio.aau.dk.

Submitted on July 21, 2005
Revised on September 26, 2005
Accepted on 2 February 2006


  Abstract
Recent work suggests that protein fibrillation mechanisms and the structure of the resulting protein fibrils are very sensitive to environmental conditions such as temperature and ionic strength. Here we report the effect of several inorganic salts on the fibrillation of glucagon. At acidic pH fibrillation is much less influenced by cations than anions, for which the effects follow the electroselectivity series; e.g., the effect of sulfate is ~65-fold higher than that of chloride per mole. Increased salt concentrations generally accelerate fibrillation, but result in formation of an alternate type of fibrils. Stability of these fibrils is highly affected by changes in anion concentration; the apparent melting temperature is increased by ~22°C for any 10-fold concentration increase, indicating that the fibrils cannot exist without anions. In contrast, fibrillation under alkaline conditions is more affected by cations than anions. We conclude that ions interact directly as structural ligands with glucagon fibrils where they coordinate charges and assist in formation of new fibrils. As ex vivo amyloid plaques often contain large amounts of highly sulfated organic molecules, the specific effects of sulfate ions on glucagon may have general relevance in the study of amyloidosis and other protein deposition diseases.

Key Words: Amyloid, Fibrillation, Kinetics, Polymorphism




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Copyright © 2006 by the Biophysical Society.