Controlled Self-Assembly of Re-engineered Insulin by FeII

Self-assembly of proteins mediated by metal ions is crucial in biological systems and a better understanding and novel strategies for its control are important. An abiotic metal ion ligand in a protein offers the prospect of control of the oligomeric state, if a selectivity over binding to the native side chains can be achieved. Insulin binds Zn-II to form a hexamer, which is important for its storage in vivo and in drug formulations. We have re-engineered an insulin variant to control its self-assembly by covalent attachment of 2,2'-bipyridine. The use of Fe-II provided chemoselective binding over the native site, forming a homotrimer in a reversible manner, which was easily followed by the characteristic color of the Fe-II complex. This provided the first well-defined insulin trimer and the first insulin variant for which self-assembly can be followed visually.