Speciation of Cyclo(Pro-Gly) 3 and Its Divalent Metal-Ion Complexes by Electrospray Ionization Mass Spectrometry

• Published in: Journal of the American Society for Mass Spectrometry Vol. 16; no. 9; pp. 1536 - 1544
• Main Authors: Ross, Andrew R.S., Luettgen, Sarah L.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01-09-2005; Elsevier Science; Springer Nature B.V
• Subjects: Abundance; Acetonitrile; Ammonium acetate; Atomic properties; Binding; Binding Sites; Chemistry; Coordination compounds; Copper; Electrospraying; Exact sciences and technology; Inorganic chemistry and origins of life; Ionization; Ions; Manganese; Mass spectrometry; Metal ions; Metals - chemistry; Models, Chemical; Models, Molecular; Nickel; Oxygen atoms; Peptide Mapping - methods; Peptides; Peptides, Cyclic - chemistry; Preparations and properties; Scientific imaging; Speciation; Spectrometry, Mass, Electrospray Ionization - methods; Spectroscopy; Strontium; Divalent metal Complexes; Collisional activation; Stability; Peptides; Cyclic peptides; Organic ligand; Fragmentation pattern; Alkaline earth metal Complexes; Transition metal Complexes; Experimental study; Electrospray; Hexapeptide; Mixed solvent; Mass spectrometry MS/MS; Hydroorganic solvent; Mass spectrometry; Speciation
• DOI: 10.1016/j.jasms.2005.05.002
• EISSN: 1879-1123
• ISSN: 1044-0305

Electrospray ionization mass spectrometry (ESI-MS) was used to study the binding of selected group II and divalent transition-metal ions by cyclo(Pro-Gly)
3 (CPG3), a model ion carrier peptide. Metal salts (CatX
n) were combined with the peptide (M) at a molar ratio of 1:10 M/Cat in aqueous solvents containing 50% vol/vol acetonitrile or methanol and 1 or 10 mM ammonium acetate (NH
4Ac). Species detected include [M + H]
+, [M + Cat − H]
+, [M
2 + Cat]
2+, [M + Cat + Ac]
+, and [M + Cat + X]
+. The relative stabilities of complexes formed with different cations (Mg
2+, Ca
2+, Sr
2+, Mn
2+, Co
2+, Ni
2+, Cu
2+, and Zn
2+) were determined from the abundance of 1:1 and 2:1 M/Cat species relative to that of the unbound peptide. The largest metal ions (Ca
2+, Sr
2+, and Mn
2+) formed the most stable complexes. Reducing the buffer concentration increased the overall extent of metal binding. Results show that the binding specificity of CPG3 depends upon the size of the metal ion and its propensity for electrostatic interaction with oxygen atoms. Product ion tandem mass spectrometry of [M + H]
+ and [M + Cu − H]
+ confirmed the cyclic structure of the peptide, although the initial site(s) of metal attachment could not be determined.