engleski

Coordination of metal ions in the 2-Mo and 2-Ni type of insulin

Insulin is a metalloprotein and in the rhombohedral crystalline form named 2-Zn insulin it is organised as a hexamer with the zinc ion octahedrally coordinated by three His imidazole ligands and three water molecules. It has been known for many years that different ions can substitute the zinc ion [1], however only a few of such complexes have been structurally characterized [2]. In the present study the zinc ion in insulin was substituted with Mo6+ and Ni2+ ions in order to investigate the difference in their metal coordination. Crystals of these insulin derivatives were obtained from zinc-free insulin under conditions analoguous to those for 2-Zn insulin but with addition of the above mentioned metal salts. The X-ray diffraction data have been collected at the synchrotron Elettra in Trieste for the 2-Ni insulin to 1.3 Å ; ; ; and at ESRF in Grenoble for the 2-Mo insulin to 1.1 Å ; ; ; resolution. In the 2-Mo insulin, one of Mo6+ ions is octahedrally coordinated by three His imidazole ligands and three water molecules, while the other is disordered with both octahedral and tetrahedral coordination present. In the 2-Ni insulin both Ni2+ ions are octahedrally coordinated by three His imidazole ligands and three water molecules. [1] T. Blundell, G. Dodson, D. Hodgkin & D. Mercola, Adv. Protein Chem. 26 (1972) 279-402. [2] C. P. Hill, Z. Dauter, E. J. Dodson, G. Dodson & M. F. Dunn, Biochemistry 30 (1991) 917-924.

insulin; metal coordination; metal replacement

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