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Crystallization and structure of the human Co- insuln derivative-a new crystal form

Insulin is synthesized in humans and other mammals within the beta cells of the islets of Langerhans in the pancreas. It is structured as a two polypeptide chains (chain A consists of 21 and chain B of 30 amino acids) linked by two sulfur bridges. Insulin is used medically in Type 1 diabetes mellitus. As a part of our ongoing research on the crystallization and structural studies on human insulin derivatives [1], [2] in the present study the zinc ions in insulin were substituted with cobalt. Cobalt plays numerous biological roles and is essential to all animals. It is a key constituent of cobalamin-based and other enzymes. Crystals of a new form of the human Co-insulin derivative were grown by the hanging drop vapour diffusion method using Zn-free insulin. The single crystal diffraction data were collected at the ELETTRA Synchrotron Light Laboratory, beam line XRD-1, to 1.23 Å resolution. The investigated insulin derivative belongs to the R3 space group (hexagonal setting) with cell parameters a = b = 45.87, c = 116.84 Å,  = 120°. There are two cobalt ions in the hexamer, coordinated octahedrally by three histidines and three water molecules. The coordination is similar as in the 2Zn-insulin in the T6 form. However, the packing of the hexamers in the unit cell is quite different than in the Zn-derivative. [1] Prugovečki B., Dodson E.J., Dodson G.G., Matković-Čalogović D. Croat. Chem. Acta, 2009, 82 (2), 433-438. [2] Prugovečki, B. ; PhD Thesis, University of Zagreb, 2005.

insulin; cobalt; X-ray

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