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Glycobiology, 2001, Vol. 11, No. 6 473-479
© 2001 Oxford University Press

Sulfatide promotes the folding of proinsulin, preserves insulin crystals, and mediates its monomerization

Thomas Osterbye1,2, Klavs H. Jørgensen2, Pam Fredman3, Jørgen Tranum-Jensen4, Anne Kaas2, Jens Brange5, Jean L. Whittingham6 and Karsten Buschard2

2Bartholin Instituttet, Kommunehospitalet, DK-1399 Copenhagen K, Denmark, 3Institute of Clinical Neuroscience, University of Göteborg, Mölndal sjukhus, SE-431 80 Mölndal, Sweden, 4Department of Medical Anatomy, Panum Instituttet, University of Copenhagen, DK-2200 Copenhagen N, Denmark, 5Brange Consult, DK-2930 Klampenborg, Denmark, and 6Department of Chemistry, University of York, Heslington, York Y010 5DD, England

Sulfatide is a glycolipid that has been associated with insulin-dependent diabetes mellitus. It is present in the islets of Langerhans and follows the same intracellular route as insulin. However, the role of sulfatide in the beta cell has been unclear. Here we present evidence suggesting that sulfatide promotes the folding of reduced proinsulin, indicating that sulfatide possesses molecular chaperone activity. Sulfatide associates with insulin by binding to the insulin domain A8–A10 and most likely by interacting with the hydrophobic side chains of the dimer-forming part of the insulin B-chain. Sulfatide has a dual effect on insulin. It substantially reduces deterioration of insulin hexamer crystals at pH 5.5, conferring stability comparable to those in beta cell granules. Sulfatide also mediates the conversion of insulin hexamers to the biological active monomers at neutral pH, the pH at the beta-cell surface. Finally, we report that inhibition of sulfatide synthesis with chloroquine and fumonisine B1 leads to inhibition of insulin granule formation in vivo. Our observations suggest that sulfatide plays a key role in the folding of proinsulin, in the maintenance of insulin structure, and in the monomerization process.

1 To whom correspondence should be addressed


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