Intramolecular condensation reactions in protonated dipeptides: Carbon monoxide, water, and ammonia losses in competition

We present a full molecular description of fragmentation reactions of protonated diglycine (H + GG) by studying their collision-induced dissociation (CID) with Xe using a guided ion beam tandem mass spectrometer (GIBMS). Analysis of the kinetic energy-dependent CID cross sections provides the 0 K barriers for the sequential H 2 O+CO and CO+NH 3 losses from H + GG as well as for the reactions involved in y 1 and a 1 ion formation, after accounting for unimolecular decay rates, internal energy of reactant ions, and multiple ionmolecule collisions. Here, seven energetic barriers are measured for the fragmentation processes of H + GG, including the loss of H 2 O and of CO at~140 and~156 kJ/mol, the combined loss of (H 2 O+CO) and of (CO+NH 3 ) at~233 and~185 kJ/mol, and formation of y 1 and a 1 ions at~191 and~212 kJ/mol, respectively, with a second channel for a 1 formation opening at~326 kJ/mol. Theoretical energies from the preceding paper are compared with our experimental energies and found to be in good agreement. This validates the mechanisms explored computationally, including unambiguous identification of the b 2 ion as protonated 2-aminomethyl-5-oxazolone, thereby allowing a complete characterization of the elementary steps of H + GG decomposition. These results also demonstrate that all reactive species are available from the ground state conformation, as opposed to involving an initial broad distribution of protonated conformers. This result verifies the utility of the "mobile proton" model for understanding the fragmentation of protonated proteins.

Section: Cross Sections For Collision-induced Dissociationsupporting

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Thermodynamics and Mechanisms of Protonated Diglycine Decomposition: A Guided Ion Beam Study

Armentrout

Heaton

2011

“…The experiments were conducted on a Finnigan MAT LCQ ion trap (IT) instrument (San Jose, CA) with ESI [40,41], an Applied Biosystems 4700 Proteomics Analyzer MALDI-TOF/TOF [42][43][44] with MALDI, and a Micromass AutoSpec-Q hybrid tandem MS with FAB ionization (Manchester, UK) [32,45].°Samples°for°the°IT°experiments were prepared by dissolving AGG in acetonitrile/water/ acetic acid 30/70/0.1 (vol:vol) to form a 2 ϫ 10 Ϫ5 mol L Ϫ1 solution, which was infused into the ESI source at a rate of 10 L min…”

Section: Tandem Mass Spectrometry (Ms/ms) Experimentsmentioning

confidence: 99%

Backbone cleavages and sequential loss of carbon monoxide and ammonia from protonated AGG: A combined tandem mass spectrometry, isotope labeling, and theoretical study

Bythell

Barofsky

Pingitore

et al. 2007

Self Cite

The fragmentation characteristics of protonated alanylglycylglycine, [AGG ϩ H] ϩ , were investigated by tandem mass spectrometry in MALDI-TOF/TOF, ion trap, and hybrid sector instruments. b 2 is the most abundant fragment ion in MALDI-TOF/TOF, ion trap, and hybrid sector metastable ion (MI) experiments, while y 2 is slightly more abundant than b 2 in collision activated dissociation (CAD) performed in the sector instrument. The A-G amide bond is cleaved on the a 1 -y 2 pathway resulting in a proton-bound dimer of GG and MeCHϭNH. Depending on the fragmentation conditions employed, this dimer can then (1) [3,4] have enabled tandem mass spectrometry (MS/MS) to become the standard tool for elucidation of peptide sequence. Gas-phase protonated peptides can be isolated, activated (usually by collision(s) with an inert gas), dissociated, and detected. The resulting spectra show that protonated peptides undergo backbone cleavages, dissociations in the side chains and losses of small neutrals (water, ammonia, carbon monoxide), or an amalgamation of these [5][6][7][8]. Experimental and computational studies have been undertaken on the backbone and side-chain fragmentations [9 -32] as well as neutral losses [11, 18, 19, 27-29, 31, 32].Peptide fragment ion spectra are utilized to sequence peptides and proteins with the help of various bioinformatics tools. Candidate peptides and their theoretical MS/MS spectra are generated in silico using protein and/or DNA databases and fragmentation models. The in silico spectra are then compared with the experimental MS/MS spectrum to find the most closely matching sequences. The success of this computer-aided peptide sequencing approach is directly related to the quality of the applied fragmentation models that summarize our present understanding of gas-phase peptide chemistry [7].The "mobile proton" fragmentation model [26,33] takes into account the energetics and reactivity of the various protonation sites of peptides. Upon excitation, the extra proton is transferred from a usually unreactive site of higher gas-phase basicity (arginine, R, or lysine, K, side chain or the N-terminal amino group) to form an energetically less favored but reactive, backboneamide-protonated species. Protonation of the amide Address reprint requests to Dr.

“…ϩ , at m/z ϭ 228, of the dipeptide is a low-energy process and typically does°not°involve°backbone°cleavages° [27].°The°onset for loss of H 2 O in HF and FH occurred at about 10V for°both°dipeptides°(Figure°4).°Sequential°losses°of ammonia dominated the high mass region of arginine containing dipeptides. It was also interesting to note the loss of NH 3 was primarily a second generation product°in°VK°(246°Ͼ°147°Ͼ°130°in°Figure°3)°and°a first generation product in the product ion spectra of KV°(246°Ͼ°229°in°Figure°5).°These°data°also°suggested the possibility of more than one competing mechanism as a possible alternative to fragmentation from a common intermediate.…”

Section: O From (M ϩ H)mentioning

confidence: 99%

A study of b₁+H₂O and b₁-ions in the product ion spectra of dipeptides containing N-terminal basic amino acid residues

Hiserodt

Brown

Swijter

et al. 2007

The product ion spectra of approximately 200 dipeptides were acquired under low-energy conditions using a triple quadrupole mass spectrometer. The spectra of dipeptides containing an N-terminal arginine (R), histidine (H), or lysine (K) were observed to yield a b 1 ϩ H 2 O ion corresponding to the protonated basic amino acid. This was equivalent to the y 1 -ion in the corresponding C-terminal isomer. The formation of a b 1 ϩ H 2 O ion was not a significant fragmentation channel in any dipeptides analyzed including those containing a C-terminal basic amino acid unless they also contained an N-terminal basic amino acid. Occurring simultaneously and under equal energy conditions an apparent b 1 -ion was formed, which has its corresponding C-terminal equivalent in the y 1 -H 2 O ion. Energy resolved mass spectrometry (ERMS), deuterium labeling, and accurate mass experiments as well as data reported were used to show the relationships between the b 1 ϩH 2 O and b 1 -ions in the dipeptides containing an N-terminal basic amino acid and the y 1 and y 1 -H 2 O ions in the corresponding C-terminal isomers. (J Am Soc Mass Spectrom 2007, 18, 1414 -1422) © 2007 American Society for Mass Spectrometry C ollision induced dissociation (CID) in a triple quadrupole mass spectrometer utilizing electrospray ionization (ESI) is a widely used technique for obtaining product ion spectra for the characterization of peptides. The spectrometric information in the product ion spectrum acquired at a single collision energy is limited and can be significantly enhanced utilizing energy resolved mass spectrometry (ERMS), where product ion spectra are acquired at increasingly greater collision cell energies. This results in an increase in the internal energy of the precursor ion, which leads to further dissociation. A plot of relative intensity versus collision energy of selected fragment ions leads to the generation of breakdown curves [1,2]. Evaluation of these breakdown curves can provide information on fragmentation mechanisms such as distinguishing between competitive and consecutive fragmentation pathways, the stability of product ions, and identification of first and subsequent generation product ions [3][4][5][6][7][8]; identification of isomers and tautomers [9 -11]; and development of library searchable product ion spectra [12,13]. Since the internal energy of the precursor ion is not rigorously known, breakdown curves provide a qualitative picture of a fragmentation mechanism.Using these analytical tools, our laboratory analyzed ϳ200 dipeptides and have made some noteworthy observations in the product ion spectra of dipeptides containing N-terminal arginine (R), histidine (H), and lysine (K) and their C-terminal isomers. We used the single letter abbreviations for amino acids in dipeptides throughout this paper.The first was the observation of a fragment ion that corresponded to the mass of the protonated molecule (M ϩ H) ϩ of the basic amino acid. This was observed at m/z ϭ 175 for arginine, m/z ϭ 156 for histidine, and m/z ϭ 147 fo...