Elucidation of the binding sites of two novel Ru(II) complexes on bovine serum albumin

• Ru(II) complexes have been characterized by mass spectrometry (MS).
• The binding of the complexes to bovine serum albumin has been conclusively proved.
• Qualitative and quantitative determination of the binding sites has been performed.
• The application of MS for determination of the binding sites is discussed.

Hyphenated mass spectrometry (MS) techniques have attained an important position in analysis of covalent and non-covalent interactions of metal complexes with peptides and proteins. The aim of the present study was to qualitatively and quantitatively determine ruthenium binding sites on a protein using tandem mass spectrometry and allied techniques, i.e. liquid chromatography (LC) and inductively coupled plasma optical emission spectrometry (ICP-OES). For that purpose, two newly synthesized Ru(II) complexes of a meridional geometry, namely mer-[Ru(4′ Cl-tpy)(en)Cl]+ (1) and mer-[Ru(4′ Cl-tpy)(dach)Cl]+ (2) (where 4′ Cl-tpy = 4′-chloro-2,2′:6′,2″-terpyridine, en = 1,2-diaminoethane and dach = 1,2-diaminocyclohexane), and bovine serum albumin were used. The binding of the complexes to the protein was investigated by means of size exclusion- and reversed phase-LC, ICP OES, matrix-assisted laser desorption ionization MS and MS/MS. Ruthenated peptide sequence and a binding target amino acid were revealed through accurate elucidation of MS/MS spectra. The results obtained in this study suggest a high binding capacity of the protein towards both complexes, with up to 5.77 ± 0.14 and 6.95 ± 0.43 mol of 1 and 2 bound per mol of protein, respectively. The proposed binding mechanism for the selected complexes includes the release of Cl ligand, its replacement with water molecule and further coordination to electron donor histidine residue.

The binding of mer-[Ru(4′ Cl-tpy)(en)Cl]+ and mer-[Ru(4′ Cl-tpy)(dach)Cl]+ (where 4′ Cl-tpy = 4′-chloro-2,2′:6′,2″-terpyridine, en = 1,2-diaminoethane and dach = 1,2-diaminocyclohexane) to bovine serum albumin has been investigated using tandem mass spectrometry and allied techniques. Histidine is revealed to be the target amino acid for the binding of both complexes.Figure optionsDownload as PowerPoint slide