Negative ion cleavages of (M-H) anions of peptides. Part 3. Post-translational modifications.

It is now 25 years since we commenced the study of the negative-ion fragmentations of peptides and we have recently concluded this research with investigations of the negative-ion chemistry of most post-translational functional groups. Our first negative-ion peptide review (Bowie, Brinkworth, & Dua, 2002) dealt with the characteristic backbone fragmentations and side-chain cleavages from (M-H) ions of underivatized peptides, while the second (Bilusich & Bowie, 2009) included negative-ion backbone cleavages for Ser and Cys and some initial data on some post-translational groups including disulfides. This third and final review provides a brief summary of the major backbone and side chain cleavages outlined before (Bowie, Brinkworth, & Dua, 2002) and describes the quantum mechanical hydrogen tunneling associated with some proton transfers in enolate anion/enolate systems.

Diagnostic di- and triphosphate cyclisation in the negative ion electrospray mass spectra of phosphoSer peptides.

It has been shown previously that [M-H](-) anions of small peptides containing two phosphate residues undergo cyclisation of the phosphate groups, following collision-induced dissociation (CID), to form a characteristic singly charged anion A (H3P2O7(-), m/z 177). In the present study it is shown that the precursor anions derived from the diphosphopeptides of caerin 1.1 [GLLSVLGSVAKHVLPHVVPVIAEHL(NH2)] and frenatin 3 [GLMSVLGHAVGNVLGGLFKPKS(OH)] also form the characteristic product anion A (m/z 177).

Histidine-containing host-defence skin peptides of anurans bind Cu2+. An electrospray ionisation mass spectrometry and computational modelling study.

Anuran peptides which contain His, including caerin 1.8 (GLFKVLGSVAKHLLPHVVPVIAEKL-NH(2)), caerin 1.2 (GLLGVLGSVAKHVLPHVVPVIAEHL-NH(2)), Ala(15) maculatin 1.

The application of negative ion electrospray mass spectrometry for the sequencing of underivatized disulfide-containing proteins: insulin and lysozyme.

Negative ion electrospray mass spectra of the peptides produced by tryptic and chymotrypsin digests of bovine insulin, and from the tryptic digest of lysozyme identify at least 80% of the sequences of these proteins. In particular, negative ion mass spectrometry identifies and positions disulfide moieties, and is the method of choice for identifying this post-translational modification in these two proteins. Intramolecular disulfide functionality is identified by the fragmentation [(M - H)(-)- H(2)S(2)](-) in a digest peptide, and CID of that fragment anion provides amino acid sequencing information.

Negative ion fragmentations of deprotonated peptides. The unusual case of isoAsp: a joint experimental and theoretical study. Comparison with positive ion cleavages.

The following peptides have been examined in this study: GLDFG(OH), caeridin 1.1 [GLLDGLLGLGGL(NH(2))], 11 Ala citropin 1.1 [GLFDVIKKVAAVIGGL(NH(2))], Crinia angiotensin [APGDRIYVHPF(OH)] and their isoAsp isomers.

Negative ion fragmentations of deprotonated peptides containing post-translational modifications: diphosphorylated systems containing Ser, Thr and Tyr. A characteristic phosphate/phosphate cyclisation. A joint experimental and theoretical study.

[M-H](-) anions from small diphosphopeptides (phosphate groups on Ser, Thr or Tyr) show characteristic peaks corresponding to m/z 177 (H(3)P(2)O(7) (-)), 159 (HP(2)O(6) (-)) and sometimes [(M-H)(-)-H(4)P(2)O(7)](-). M/z 177 and m/z 159 are major peaks in the spectra of small peptides with 1,2, 1,3, 1,4, 1,5 and 1,6 diphosphate substitution, which means that the decomposing [M-H](-) anions must have flexible structures in order for the two phosphate groups to interact with each other. Peptides where the two phosphate groups are more than six amino acid residues apart have not been studied.

Negative ion fragmentations of deprotonated peptides containing post-translational modifications. An unusual cyclisation/rearrangement involving phosphotyrosine; a joint experimental and theoretical study.

The characteristic fragmentations of a pTyr group in the negative ion electrospray mass spectrum of the [M-H](-) anion of a peptide or protein involve the formation of PO(3) (-) (m/z 79) and the corresponding [(M-H)(-)-HPO(3)](-) species. In some tetrapeptides where pTyr is the third residue, these characteristic anion fragmentations are accompanied by ions corresponding to H(2)PO(4) (-) and [(M-H)(-)-H(3)PO(4)](-) (these are fragmentations normally indicating the presence of pSer or pThr). These product ions are formed by rearrangement processes which involve initial nucleophilic attack of a C-terminal -CO(2) (-) [or -C(==NH)O(-)] group at the phosphorus of the Tyr side chain [an S(N)2(P) reaction].

Characteristic negative ion fragmentations of deprotonated peptides containing post-translational modifications: mono-phosphorylated Ser, Thr and Tyr. A joint experimental and theoretical study.

Peptides and proteins may contain post-translationally modified phosphorylated amino acid residues, in particular phosphorylated serine (pSer), threonine (pThr) and tyrosine (pTyr). Following earlier work by Lehmann et al., the [M-H]- anions of peptides containing pSer and pThr functionality show loss of the elements of H3PO4.

The formation of the stable radicals .CH2CN, CH3.CHCN and .CH2CH2CN from the anions -CH2CN, CH3-CHCN and -CH2CH2CN in the gas phase. A joint experimental and theoretical study.

Franck-Condon one-electron oxidation of the stable anions -CH2CN, CH3-CHCN and -CH2CH2CN (in the collision cell of a reverse-sector mass spectrometer) produce the radicals .CH2CN, CH3.CHCN and .