Probing the stability and structure of metalloporphyrin complexes with basic peptides by mass spectrometry

Eur. J. Mass Spectrom. 11, 65–75 (2005)
DOI: 10.1255/ejms.704

Probing the stability and structure of metalloporphyrin complexes with basic peptides by mass spectrometry

Emily E. Jellen and Victor Ryzhov^*
Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115, USA

ABSTRACT:

The stability and structure of non-covalent complexes of various peptides contatining basic amino acid residues (Arg, Lys) with metalloporphyrins were studied in a quadrupole ion trap mass spectrometer. The complexes of heme and three other metalloporphyrins with a variety of basic peptides and model systems were formed via electrospray ionization (ESI) and their stability was probed by energy- variable collision-induced dissociation (CID). A linear dependence for basic peptides and model compounds/metalloporphyrin complexes was observed in the plots of stability versus degrees of freedom and was used to evaluate relative bond strength. These results were then compared with previous data obtained for complexes of metalloporphyrins with His-containing peptides and peptides containing no basic amino acids. The binding strengths of Lys-containing peptide complexes in the gas phase was found to be almost as strong as that of Arg-containing complexes. Both systems showed stronger binding than His-containing peptides studied previously. To probe the structure of Arg and Lys non- covalent complexes (charge solvation versus salt bridges), two techniques, CID and ion–molecule reactions, were used. CID experiments indicate that the gas-phase complexes are most likely formed by charge solvation of the central metal ion in the metalloporphyrin by basic side chains of Arg or Lys. Results from the ion–molecule reaction studies are consistent with the charge solvation structure as well.

Keywords: non-covalent complexes, quadrupole ion trap mass spectrometry, collision-induced dissociation, ion- molecule reactions, metalloporphyrin-ligand binding.

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