Search

The interaction of a series of doubly charged metal cations (M2+ = Ca, Co, Ni, Cu, and Zn) with angiotensin I (AngI, Asp1-Arg2-Val3-Tyr4-Ile5-His6-Pro7-Phe8-His9-Leu10) is examined by collision-induced dissociation (CID) and ion mobility spectrometry–mass spectrometry (IMS–MS). The series of CID patterns combined with IMS–MS data for [AngI+M+H]3+ ions provides information about the metal–peptide binding sites. Overall, Ca2+ favors association with oxygen atoms spanning the peptide backbone; whereas, the transition metals favor binding at a site that involves association at the His6 and His9 sites. From these experiments, it is possible to derive insight into the populations of different metal coordination sites that are sampled in solution prior to introduction of species into the gas phase.

Ion mobility/mass spectrometry techniques have been used to generate a cross section database containing 1772 entries (147 singly-, 1325 doubly-, and 300 triply-charged) for protonated and alkalated tryptic peptide ions. Such a large number of values make it possible to assess the influence of alkali metal cations [where the cation (M+) corresponds to Li+ ,N a + ,K + ,o r Cs +] on peptide ion conformation. Peptide ion sizes generally increase with increasing cation size relative to the respective singly- or doublyprotonated species. Intrinsic size parameters for individual amino acid residues for alkali [Pep+M+H] 2+

Cross sections for 61 palmitoylated peptides and 73 cysteine-unmodified peptides are determined and used together with a previously obtained tryptic peptide library to derive a set of intrinsic size parameters (ISPs) for the palmitoyl (Pal) group (1.26 ± 0.04), carboxyamidomethyl (Am) group (0.92 ± 0.04), and the 20 amino acid residues to assess the influence of Pal- and Am-modification on cysteine and other amino acid residues. These values highlight the influence of the intrinsic hydrophobic and hydrophilic nature of these modifications on the overall cross sections. As a part of this analysis, we find that ISPs derived from a database of a modifier on one amino acid residue (Cys Pal ) can be applied on the same modification group on different amino acid residues (Ser Pal and Tyr Pal ). Using these ISP values, we are able to calculate peptide cross sections to within ±2% of experimental values for 83% of Pal-modified peptide ions and 63% of Am-modified peptide ions. We propose that modification groups should be treated as individual contribution factors, instead of treating the combination of the particular group and the amino acid residue they are on as a whole when considering their effects on the peptide ion mobility features.