Mass and charge state assignment for proteins and peptide mixtures via noncovalent adduction in electrospray mass spectrometry

Abstract

A method has been developed that takes advantage of the formation of noncovalent compounds in electrospray mass spectrometry. Mixtures of proteins and peptides are shown to produce an intense ion that corresponds to a 1:1 complex with a crown ether (18-crown-6). Although the crown ether may be added directly to the solution, for the current experiments it is introduced via the methanol liquid sheath. The spacing of these complexed species in the mass spectrum allows unambiguous determination of the charge state of the ions and their actual mass. Through constant neutral loss scans, charge state may be determined, mass assigned, spectra simplified, and chemical noise may be reduced for the analysis of complex peptide samples without Chromatographic separation. Finally, the prevalence of single complexation permits mass assignments based on the mass difference of a single protein ion and its complexed form at any charge state. In essence, the method performs a separation based on charge state. It can be used to complement Chromatographic separation and deconvolution algorithms for the electrospray mass spectrometry analysis of peptide-protein mixtures.

Non-covalent complexes between DNA-binding drugs and double-stranded deoxyoligonucleotides: a study by ionspray mass spectrometry

“…In cases where sufficient resolution to assign the charge state from the isotopic pattern is not available, such as often happens with linear quadrupole analysers, the correct assignment can be made by measuring the distance between the signal and known adducts with some components of the mobile phase, either occurring incidentally such as sodium and/or potassium ions, or added on purpose such as crown ethers. 51 In the present case, the correct assignment to the monomer is possible by looking at the sodium adducts of m/z 1214 (di †ering from the deprotonated ion by 22/3 u) and m/z 1822 (di †ering by 22/2 u). Incidentally, the term "adductÏ does not appear to be strictly correct to describe such ions, since e †ectively here a sodium ion has replaced one mobile hydrogen in the molecule, and is not simply added to it ; however, it is generally accepted in similar cases, and hence it will be used also in this paper.…”

Characterization of permethylated β-cyclodextrin-peptide noncovalently bound complexes using electron capture dissociation mass spectrometry (ECD MS)

“…FTICR operational parameters were optimized to maximize the abundance of the [A:CD+2H] 2+ peak, which was then subject to SWIFT isolation and to the subsequent ECD MS. The generation of noncovalent complexes [M:CD+2H] 2+ has previously been well documented in the literature [13][14][15][16][17][18][19][20][21][22][23][24][25][26]. The formation of noncovalent complexes, not covalent ones, was confirmed by performing sustained off-resonance irradiation collisionally activated dissociation (SORI-CAD) on the complex, which resulted in disassembly of the complex into its constituent ␤-CD and peptide (data not shown here) [48].…”

“…Many investigators have reported, on the basis of favorable 1:1 complex formation with aromatic group-containing compounds, that CD-guest noncovalent complexes formed in the gas phase were inclusion complexes that reflected the interactions in solution [14][15][16][17][18][19][20]. In contrast, Cunniff and Vouros reported that CD mixtures with amino acids or small peptides that might be least likely to form hydrophobic inclusion complexes in solution generally showed the most intense complex ions in their ESI-MS experiments [13]. Based on this finding, they suggested that the CD complexes were likely to be electrostatic adducts formed during the ESI process.…”

“…However, there has been an ongoing debate about whether mass spectrometric detection of noncovalent complexes in the gas-phase genuinely reflects interactions in solution. For gas-phase host-guest complexes involving CDs, extensive studies have been carried out due to this system's potential for examining inclusion complexes [4,[13][14][15][16][17][18][19][20][21][22][23][24][25][26]. Using electrospray ionization mass spectrometry (ESI-MS), a variety of CD-guest (e.g., drugs, steroid hormones, amino acids, and peptides) noncovalent complexes have been detected and analyzed.…”

Theoretical study of the separation of valine enantiomers by β-cyclodextrin with different solvents: a molecular mechanics and dynamics simulation

“…8,9 Inclusion complex formation and chiral separation of amino acids and amino acid derivatives by CDs have been studied with different experimental techniques such as electrospray mass spectrometry, capillary electrophoresis and gas chromatography. [10][11][12][13][14] They have also been theoretically studied by molecular mechanics 15 and dynamics. 13,16,17 In these theoretical studies the presence of organic modifiers is represented by different values of the dielectric constant in the electrostatic contribution to the interaction energy.…”