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Issue 13, 2011
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Effect of the N-terminal basic residue on facile Cα–C bond cleavages of aromatic-containing peptide radical cations

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Abstract

Fragmentation of radical cationic peptides [R(G)n−2X(G)7−n+ and [R(G)m−2XG]˙+ (X = Phe or Tyr; m = 2–5; n = 2–7) leads selectively to an+ product ions through in situ Cα–C peptide backbone cleavage at the aromatic amino acid residues. In contrast, substituting the arginine residue with a less-basic lysine residue, forming [K(G)n−2X(G)7−n+ (X = Phe or Tyr; n = 2–7) analogs, generates abundant b–y product ions; no site-selective Cα–C peptide bond cleavage was observed. Studying the prototypical radical cationic tripeptides [RFG]˙+ and [KFG]˙+ using low-energy collision-induced dissociation and density functional theory, we have examined the influence of the basicity of the N-terminal amino acid residue on the competition between the isomerization and dissociation channels, particularly the selective Cα–C bond cleavage via β-hydrogen atom migration. The dissociation barriers for the formation of a2+ ions from [RFG]˙+ and [KFG]˙+via their β-radical isomers are comparable (33.1 and 35.0 kcal mol−1, respectively); the dissociation barrier for the charge-induced formation of the [b2 − H]˙+ radical cation from [RFG]˙+via its α-radical isomer (39.8 kcal mol−1) was considerably higher than that from [KFG]˙+ (27.2 kcal mol−1). Thus, the basic arginine residue sequesters the mobile proton to promote the charge-remote selective Cα–C bond cleavage by energetically hindering the competing charge-induced pathways.

Graphical abstract: Effect of the N-terminal basic residue on facile Cα–C bond cleavages of aromatic-containing peptide radical cations

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Publication details

The article was received on 24 Jun 2010, accepted on 20 Jan 2011 and first published on 17 Feb 2011


Article type: Paper
DOI: 10.1039/C0CP00974A
Citation: Phys. Chem. Chem. Phys., 2011,13, 5888-5896
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    Effect of the N-terminal basic residue on facile Cα–C bond cleavages of aromatic-containing peptide radical cations

    M. Xu, T. Song, Q. Quan, Q. Hao, D. Fang, C. Siu and I. K. Chu, Phys. Chem. Chem. Phys., 2011, 13, 5888
    DOI: 10.1039/C0CP00974A

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