Metal ion assisted folding and supramolecular organization of a de novo designed metalloprotein

This paper describes the supramolecular organization of a novel de novo designed metalloprotein, which consists of two N-terminal terpyridine modified coiled-coil protein folding motif sequences held together by an iron(II) ion. The self-assembly of the metalloprotein is the result of the interplay of metal ion complexation and protein folding, and can be manipulated by changes in concentration, temperature, and solvent. At low concentrations, folding and organization of the metalloprotein resembles that of the native coiled-coil peptide. Besides unimeric species, also dimeric and tetrameric metalloprotein assemblies were found. Several indications suggest that at least part of these unimeric species may exist as intramolecularly folded coiled-coils, however, unambiguous proof is lacking at the moment. At higher concentrations, folding and organization is dominated by the large octahedral [Fe-II(terpy)(2)] complexes (terpy = 2,2':6',2'-terpyridine) and considerable amounts of large, ill-defined aggregates are formed.