Sulfatide Preserves Insulin Crystals Not by Being Integrated in the Lattice but by Stabilizing Their Surface

Figure 1

(a) Electron microscopy of a beta cell stained for sulfatide with colloidal gold granules as secondary indications. Close relationship to the insulin crystals is clearly seen. At the surface at the beta cells an insulin crystal close to exocytosis is clearly seen at one quartile from the right in the horizontal axis and half down in the vertical axis. (b) Upon crystallization, insulin formed hexamers of approximately 100 μm diameter. ((c) and (d)) Structure of insulin crystallized in the presence of sulfatide shows classic features of zinc bound insulin hexamers. (c) The crystals structure of insulin (PDB code 4XC4). Zinc is depicted as gray spheres. (d) An electron density map surrounding the disulfide bond linking cysteine chain A 20 to cysteine chain B 19.

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