Site-specific modification of de novo designed coiled-coil polypeptides with inorganic redox complexes

A stepwise procedure for preparing of site-specific binuclear metallopeptides is described. The modification procedure involves the alkylation of a cysteine side chain by reaction with [Ru(bpy)(2)(phen-ClA)](2+), where bpy = 2,2'-bipyridine and phen-ClA = 5-chloroacetamido-1,10-phenanthroline, followed by the coordination of a ruthenium pentammine complex to a histidine residue located elsewhere along the sequence. The apo and metalated versions of the peptides C10H21(30-mer) and H10C21(30-mer) display circular dichroism spectra having minima at 208 and 222 nm, with theta(222)/theta(208) = 1.04 to indicate that these peptides exist as alpha-helical coiled-coils in aqueous solution. When the ruthenium polypyridyl complex is attached to C10H21(30-mer), the Delta-l and Lambda-l diastereomers of the resulting metallopeptide can be readily separated from each other by reversed-phase HPLC. However, in the case of the related H10C21(30-mer) metallopeptide, the two diastereomers cannot be chromatographically resolved. These results indicate how the subtle interplay between peptide conformation/sequence and metal complex geometry may alter some of the physical characteristics of metallopeptides.