Determination of a Binding Site of Cu and Ni Metal Ions with Oxytocin Peptide by Electrospray Tandem Mass Spectrometry and Multiple Mass Spectrometry

Abstract

The structures of a [Ni(II), Cu(II)- - -oxytocin] complex were investigated by electrospray ionization-mass spectrometry in positive mode. The fragmentation patterns of the [Ni(II), Cu(II) + OT](2+) complex were analyzed by tandem mass spectrometry and multiple mass spectrometry in the gas-phase. Conformations of metalII ion binding to oxytocin (OT) have been studied to explain the biological activity difference in the physiological solution. The [Ni(II) + OT](2+) and [Cu(II) + OT](2+) complexes were observed as the main ions in MS spectra. The Cys1-Tyr2-Ile3-Gln4 sequence of oxytocin is suggested to be a binding site for the [Ni(II) + OT](2+) gas-phase complex and Ile3-Gln4-Asn5-Cys6 sequence for the [Cu(II) + OT](2+) gas-phase complex. The specific binding site of CuII ion in the [Cu(II) + OT](2+) complex is explained as a reason of the negligible effect on the [Cu(II)- - -oxytocin] biological activity in aqueous solution.