This paper presents results of the structural investigation on the human insulin hexamer derivative stabilised by nickel coordination. Single crystals of the Ni-insulin derivative were prepared by the hanging drop vapour diffusion crystallisation method using metal-free insulin and nickel(II) acetate tetrahydrate. The low-temperature crystal structure was determined by the single crystal X-ray crystallographic method with data extending to 1.35 Å spacing. The investigated insulin derivative exhibits the T6 form of insulin and crystallizes in the trigonal system in space group R3, with the unit cell parameters a = b = 81.41 Å and c = 33.75 Å. There are two nickel atoms per insulin hexamer and both are octahedrally coordinated by three Nε2 atoms of three symmetry-related HisB10/HisD10 and three oxygen atoms of three symmetry-related water molecules
