High Resolution Structure of the Manganese Derivative of Insulin

The structure of the human manganese derivative of insulin was determined using the single crystal X-ray diffraction method. Single crystals were grown by the hanging drop vapour diffusion crystallization method using zinc-free insulin and manganese(II) sulphate monohydrate in citrate buffer at pH = 6.4. It crystallizes in the trigonal system in the space group R 3 with the unit cell parameters: a = b = 81.70 angstrom and c = 33.73 angstrom. There are two manganese ions per insulin hexamer in the human manganese-insulin derivative. The manganese ions lie on the three-fold crystallographic axis on opposite sides of the hexamer. Both manganese ions are octahedrally coordinated by three N-epsilon 2 atoms from the imidazolyl side chains of three symmetry-related HisB10/HisD10 and three oxygen atoms of three symmetry-related water molecules. The investigated human manganese-insulin derivative adopts the T-6 conformation. (doi: 10.5562/cca2108)