Metal induced structural changes observed in hexameric insulin

Abstract The metal ions in insulin hexamer play a crucial role in the T to R conformational transitions. We have determined the crystal structures of 2Mn 2+ , 1Rb 1+ and 4Ni 2+ human arg-insulin and compared them with the 2Zn 2+ structure. The first two structures exist in the T3R3 f state like the native 2Zn 2+ arg-insulin, while the 4Ni 2+ adopts a T6 conformation. The metal coordination is found to be tetrahedral in all the structures except that of nickel where a dual octahedral and tetrahedral coordination is found at one site. Rubidium occupies only one of the high affinity metal binding sites. The metal induced structural changes observed, have been explained.