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

Abstract

All rights reserved EuroPEAN JourNAL of MASS SPEctroMEtry oxytocin secreted in the posterior pituitary is a well characterized peptide hormone that elicits contraction of the uterus, smoothes muscles during lactation and feels an affinity with the brain.1 oxytocin consists of nine amino acids (cysteine1-tyrosine2-Isoluecine3-Glutamine4-Asparagine5-cysteine6-Proline7-Leucine8-Glycine9) and an amidated c-terminus.2 the synthesis of an octapeptide amide with the hormonal activity was reported by Vigneaud et al. 3 A cyclic structure involving the formation of a cys1-cys6 disulfide bridge of oxytocin has been proposed.2,4 two b-turn structures were also reported on the basis of the results of NMr spectroscopy experiments involving oxytocin. [5][6][7] A first b-turn structure was proposed in a cyclic cys1-tyr2-Ile3-Gln4-Asn5-cys6 pentapeptide involving the sequence tyr2-Ile3-Gln4-Asn5, and a second b-turn structure was proposed in the c-terminal sequence cys6-Pro7-Leu8-Gly9.the structure of oxytocin complexed with a receptor 8-9 and the biological activities of [metal ion---oxytocin] complex [10][11][12][13][14][15][16][17] have been studied by many research groups.

Binding of Cu+ and Cu2+ with peptides: Peptides = oxytocin, Arg8‐vasopressin, bradykinin, angiotensin‐I, substance‐P, somatostatin, and neurotensin

“…However, ligation of Cu 2+ is predicted to be −4 N of Ile 3 ‐Gln 4 ‐Asn 5 ‐Cys 6 at pH ~7, and it changes to −4 N of Cys 1 ‐Tyr 2 ‐Ile 3 ‐Gln 4 at pH ~5 to 7. At pH ~3, Cu 2+ binds with −4O instead of −4 N amide of Tyr 2 ‐Ile 3 ‐Cys 6 ‐Gly 9 residues . In addition, the [OT‐Cu 2+ ] complex shows unique fragmentation pattern with abundant b ‐type ions in CID, ECD, and electron transfer dissociation, which is assumed to be the reduction of Cu 2+ to Cu + by electron capture/transfer processes .…”

“…It was found that the divalent ions, in particular, Zn 2+ , in the aspirate buffer is more effective in improving its thermal stability. 54 Recently, Clemmer's group [59][60][61][62] In addition, the [OT-Cu 2+ ] complex shows unique fragmentation pattern with abundant b-type ions in CID, ECD, and electron transfer dissociation, which is assumed to be the reduction of Cu 2+ to Cu + by electron capture/transfer processes. 63,64 Thus, most of the MS studies deal with fragmentation pattern, pHdependent binding behavior, and the AAs involved in the binding of Cu 2+ and OT.…”

Electrospray Ionization Mass Spectrometric Approach of Conformationally-Induced Metal Binding to Oligopeptides

“…1 for example, the structures of oxytocin complexes with nickel and copper ions were investigated by this technique. 2 tandem mass spectrometry has been used to yield singly-and multiply charged fragment ions that can be assigned to the known sequence of the protein. 3 ESI tandem mass spectrometry (MS/MS) experiments were used to provide evidence regarding the sites of interactions between zinc metal ions and angiotensin peptides.…”

“…6 conformations of metal ions binding to peptides have been studied to explain the biological activity difference in the physiological solution. 2 Besides, the copper(II) and nickel(II) binding ability of the multi-histidine peptide N-acetyl-His-Pro-His-His-NH 2 has been studied by combined pH-potentiometry and visible, circular dichroism (cD) and electron paramagnetic resonance (EPr) spectroscopies. 7 conformationally-induced metal ion binding to peptides seems to be involved in the generation of reactive oxygen species and mitochondrial dysfunction, being implicated in numerous but devastating classes of neurodegenerative disorders.…”

Investigation of metal modulation of oxytocin structure receptor-mediated signaling

“…3 These discrepancies may be in part due to the strong pHdependence of Cu(II) complexation. 4,9,10 CID and electron-capture dissociation (ECD) MS measurements alongside calculations have shown that at pH 10, Cu(II) coordinates the backbone nitrogens of Cys1, Cys6, Leu8, and Gly9. 11 Lowering the pH to pH 5 allows Cu(II) to coordinate the backbone nitrogens of the Cys1, Tyr2, Ile3, Gln4 segment.…”