Exploring metal complexes-protein/peptide interactions by high resolution mass spectrometry

Electrospray ionization high resolution mass spectrometry was used to explore the interactions occurring between metal complexes and proteins/peptides. In a first study three medicinally relevant compounds, cisplatin, transplatin and the organometallic ruthenium compound RAPTA-C, were reacted with a pool of three proteins, ubiquitin, cytochrome c and superoxide dismutase, and the reaction products were analysed using high resolution mass spectrometry. The formation of metal-protein adducts was clearly observed for the three proteins. In addition, valuable information was obtained on the nature of the protein-bound metallofragments, on their distribution among the three different proteins and on the binding kinetics. The platinum compounds were less reactive and considerably less selective in protein binding than RAPTA-C, which showed a high affinity towards ubiquitin and cytochrome c, but not superoxide dismutase. In addition, competition studies between cisplatin and RAPTA-C showed that the two metallodrugs upon protein binding manifest high affinity for the same amino acid residues. In a second study the ruthenium complex fac-[Ru(CO)3Cl2(N1-thz)] was reacted with two peptides, human β amyloid 1-42 and human β amyloid 1-28, and the reaction products were analysed using high resolution mass spectrometry. The MS spectra suggested a prevalent 1:1 metal-peptides stoichiometry and disclosed the nature of peptide-bound metallic fragments.