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Li Y, Li M, Spencer DM, Martens J, Berden G, Oomens J, Siu CK, Chu IK. Mechanistic examination of C α -C β tyrosyl bond cleavage: Spectroscopic investigation of the generation of α-glycyl radical cations from tyrosyl (glycyl/alanyl)tryptophan. JOURNAL OF MASS SPECTROMETRY : JMS 2020; 56:e4630. [PMID: 32812311 DOI: 10.1002/jms.4630] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Revised: 07/20/2020] [Accepted: 07/21/2020] [Indexed: 06/11/2023]
Abstract
In this study, dissociative one-electron transfer dissociation of [CuII (dien)Y(G/A)W]•2+ [dien = diethylenetriamine; Y(G/A)W = tyrosyl (glycyl/alanyl)tryptophan] was used to generate the tripeptide radical cations [Y(G/A)W]•+ ; subsequent loss of the Tyr side chain formed [Gα • (G/A)W]+ . The π-centered species [YGWπ • ]+ generated the α-centered species [Gα • GW]+ through Cα -Cβ bond cleavage, as revealed using infrared multiple photon dissociation (IRMPD) measurements and density functional theory (DFT) calculations. Comparisons of experimental and theoretical IR spectra confirmed that both the charge and spin densities of [Y(G/A)Wπ • ]+ were delocalized initially at the tryptophan indolyl ring; subsequent formation of the final [Gα • (G/A)W]+ structure gave the highest spin density at the α-carbon atom of the N-terminal glycine residue, with a proton solvated by the first amide oxygen atom. The IRMPD mass spectra and action spectra of the [Gα • (G/A)W]+ species were all distinctly different from those of their isomeric [G(G/A)Wπ • ]+ species. The mechanism of formation of the captodative [Gα • (G/A)W]+ species-with the charge site separated from the radical site-from [Y(G/A)Wπ • ]+ has been elucidated. DFT calculations suggested that the Cα -Cβ bond cleavage of the tyrosine residue in the radical cationic [Y(G/A)Wπ • ]+ precursor involves (a) through-space electron transfer between the indolyl and phenolic groups; (b) formation of proton-bound dimers through Cα -Cβ cleavage of the tyrosine residue; and (c) a concerted proton rearrangement from the phenolic OH group to the carboxyl group and formation of the α-carbon-centered product [Gα • (G/A)W]+ through hydrogen bond cleavage. The barriers for the electron transfer (a), the Cα -Cβ cleavage (b), and the protonation rearrangement (c) were 12.8, 26.5, and 10.3 kcal mol-1 , respectively.
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Affiliation(s)
- Yinan Li
- Department of Chemistry, The University of Hong Kong, Pokfulam, Hong Kong SAR, China
| | - Mengzhu Li
- Department of Chemistry, The University of Hong Kong, Pokfulam, Hong Kong SAR, China
| | - Daniel M Spencer
- Department of Chemistry, The University of Hong Kong, Pokfulam, Hong Kong SAR, China
| | - Jonathan Martens
- FELIX Laboratory, Institute for Molecules and Materials, Radboud University, Nijmegen, The Netherlands
| | - Giel Berden
- FELIX Laboratory, Institute for Molecules and Materials, Radboud University, Nijmegen, The Netherlands
| | - Jos Oomens
- FELIX Laboratory, Institute for Molecules and Materials, Radboud University, Nijmegen, The Netherlands
| | - Chi-Kit Siu
- Department of Chemistry, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China
| | - Ivan K Chu
- Department of Chemistry, The University of Hong Kong, Pokfulam, Hong Kong SAR, China
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2
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Mu X, Lau JKC, Lai CK, Siu KWM, Hopkinson AC, Chu IK. Isomerization versus dissociation of phenylalanylglycyltryptophan radical cations. Phys Chem Chem Phys 2017. [PMID: 28631796 DOI: 10.1039/c7cp02355c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Four isomers of the radical cation of tripeptide phenylalanylglycyltryptophan, in which the initial location of the radical center is well defined, have been isolated and their collision-induced dissociation (CID) spectra examined. These ions, the π-centered [FGWπ˙]+, α-carbon- [FGα˙W]+, N-centered [FGWN˙]+ and ζ-carbon- [Fζ˙GW]+ radical cations, were generated via collision-induced dissociation (CID) of transition metal-ligand-peptide complexes, side chain fragmentation of a π-centered radical cation, homolytic cleavage of a labile nitrogen-nitrogen single bond, and laser induced dissociation of an iodinated peptide, respectively. The π-centered and tryptophan N-centered peptide radical cations produced almost identical CID spectra, despite the different locations of their initial radical sites, which indicated that interconversion between the π-centered and tryptophan N-centered radical cations is facile. By contrast, the α-carbon-glycyl radical [FGα˙W]+, and ζ-phenyl radical [Fζ˙GW]+, featured different dissociation product ions, suggesting that the interconversions among α-carbon, π-centered (or tryptophan N-centered) and ζ-carbon-radical cations have higher barriers than those to dissociation. Density functional theory calculations have been used to perform systematic mechanistic investigations on the interconversions between these isomers and to study selected fragmentation pathways for these isomeric peptide radical cations. The results showed that the energy barrier for interconversion between [FGWπ˙]+ and [FGWN˙]+ is only 31.1 kcal mol-1, much lower than the barriers to their dissociation (40.3 kcal mol-1). For the [FGWπ˙]+, [FGα˙W]+, and [Fζ˙GW]+, the barriers to interconversion are higher than those to dissociation, suggesting that interconversions among these isomers are not competitive with dissociations. The [z3 - H]˙+ ions isolated from [FGα˙W]+ and [Fζ˙GW]+ show distinctly different fragmentation patterns, indicating that the structures of these ions are different and this result is supported by the DFT calculations.
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Affiliation(s)
- Xiaoyan Mu
- Department of Chemistry, The University of Hong Kong, Hong Kong, China.
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3
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Mu X, Song T, Siu CK, Chu IK. Tautomerization and Dissociation of Molecular Peptide Radical Cations. CHEM REC 2017. [DOI: 10.1002/tcr.201700013] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- Xiaoyan Mu
- Department of Chemistry; University of Hong Kong; Pokfulam, Hong Kong SAR P. R. China
| | - Tao Song
- Department of Chemistry; University of Hong Kong; Pokfulam, Hong Kong SAR P. R. China
| | - Chi-Kit Siu
- Department of Biology and Chemistry; City University of Hong Kong; 83 Tat Chee Avenue Kowloon Tong, Hong Kong SAR P. R. China
| | - Ivan K. Chu
- Department of Chemistry; University of Hong Kong; Pokfulam, Hong Kong SAR P. R. China
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Jang I, Lee SY, Hwangbo S, Kang D, Lee H, Kim HI, Moon B, Oh HB. TEMPO-Assisted Free Radical-Initiated Peptide Sequencing Mass Spectrometry (FRIPS MS) in Q-TOF and Orbitrap Mass Spectrometers: Single-Step Peptide Backbone Dissociations in Positive Ion Mode. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2017; 28:154-163. [PMID: 27686973 DOI: 10.1007/s13361-016-1508-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2016] [Revised: 08/15/2016] [Accepted: 09/13/2016] [Indexed: 06/06/2023]
Abstract
The present study demonstrates that one-step peptide backbone fragmentations can be achieved using the TEMPO [2-(2,2,6,6-tetramethyl piperidine-1-oxyl)]-assisted free radical-initiated peptide sequencing (FRIPS) mass spectrometry in a hybrid quadrupole time-of-flight (Q-TOF) mass spectrometer and a Q-Exactive Orbitrap instrument in positive ion mode, in contrast to two-step peptide fragmentation in an ion-trap mass spectrometer (reference Anal. Chem. 85, 7044-7051 (30)). In the hybrid Q-TOF and Q-Exactive instruments, higher collisional energies can be applied to the target peptides, compared with the low collisional energies applied by the ion-trap instrument. The higher energy deposition and the additional multiple collisions in the collision cell in both instruments appear to result in one-step peptide backbone dissociations in positive ion mode. This new finding clearly demonstrates that the TEMPO-assisted FRIPS approach is a very useful tool in peptide mass spectrometry research. Graphical Abstract ᅟ.
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Affiliation(s)
- Inae Jang
- Department of Chemistry, Sogang University, Seoul, 04107, Korea
| | - Sun Young Lee
- College of Pharmacy, Kyung Hee University, Seoul, 02447, Korea
| | - Song Hwangbo
- Department of Chemistry, Sogang University, Seoul, 04107, Korea
| | - Dukjin Kang
- Center for Bioanalysis, Division of Metrology for Quality of Life, Korea Research Institute of Standards and Science, Daejeon, 34113, Korea
| | - Hookeun Lee
- Gachon Institute of Pharmaceutical Sciences, Gachon University, Incheon, 21936, Korea
| | - Hugh I Kim
- Department of Chemistry, Korea University, Seoul, 02841, Korea
| | - Bongjin Moon
- Department of Chemistry, Sogang University, Seoul, 04107, Korea
| | - Han Bin Oh
- Department of Chemistry, Sogang University, Seoul, 04107, Korea.
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Mu X, Lau JKC, Lai CK, Siu KWM, Hopkinson AC, Chu IK. Nucleophilic substitution by amide nitrogen in the aromatic rings of [zn - H]˙⁺ ions; the structures of the [b₂ - H - 17]˙⁺ and [c1 - 17]⁺ ions. Phys Chem Chem Phys 2016; 18:11168-75. [PMID: 27048940 DOI: 10.1039/c6cp00405a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Peptide radical cations that contain an aromatic amino acid residue cleave to give [zn - H]˙⁺ ions with [b2 - H - 17]˙⁺ and [c1 - 17](+) ions, the dominant products in the dissociation of [zn - H]˙⁺, also present in lower abundance in the CID spectra. Isotopic labeling in the aromatic ring of [Yπ˙GG](+) establishes that in the formation of [b2 - H - 17]˙⁺ ions a hydrogen from the δ-position of the Y residue is lost, indicating that nucleophilic substitution on the aromatic ring has occurred. A preliminary DFT investigation of nine plausible structures for the [c1 - 17](+) ion derived from [Y(π)˙GG](+) shows that two structures resulting from attack on the aromatic ring by oxygen and nitrogen atoms from the peptide backbone have significantly better energies than other isomers. A detailed study of [Y(π)˙GG](+) using two density functionals, B3LYP and M06-2X, with a 6-31++G(d,p) basis set gives a higher barrier for attack on the aromatic ring of the [zn - H]˙⁺ ion by nitrogen than by the carbonyl oxygen. However, subsequent rearrangements involving proton transfers are much higher in energy for the oxygen-substituted isomer leading to the conclusion that the [c1 - 17](+) ions are the products of nucleophilic attack by nitrogen, protonated 2,7-dihydroxyquinoline ions. The [b2 - H - 17]˙⁺ ions are formed by loss of glycine from the same intermediates involved in the formation of the [c1 - 17](+) ions.
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Affiliation(s)
- Xiaoyan Mu
- Department of Chemistry, The University of Hong Kong, Hong Kong, China.
| | - Justin Kai-Chi Lau
- Department of Chemistry and Centre for Research in Mass Spectrometry, York University, 4700 Keele Street, Toronto ON, M3J 1P3, Canada. and Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset Avenue, Windsor, ON N9B 3P4, Canada
| | - Cheuk-Kuen Lai
- Department of Chemistry, The University of Hong Kong, Hong Kong, China.
| | - K W Michael Siu
- Department of Chemistry and Centre for Research in Mass Spectrometry, York University, 4700 Keele Street, Toronto ON, M3J 1P3, Canada. and Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset Avenue, Windsor, ON N9B 3P4, Canada
| | - Alan C Hopkinson
- Department of Chemistry and Centre for Research in Mass Spectrometry, York University, 4700 Keele Street, Toronto ON, M3J 1P3, Canada.
| | - Ivan K Chu
- Department of Chemistry, The University of Hong Kong, Hong Kong, China.
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Tang WK, Leong CP, Hao Q, Siu CK. Theoretical examination of competitive β-radical-induced cleavages of N–Cα and Cα–C bonds of peptides. CAN J CHEM 2015. [DOI: 10.1139/cjc-2015-0208] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Selective cleavages of N–Cα and Cα–C bonds of β-radical tautomers of amino acid residues in radical peptides have been examined theoretically by means of the density functional theory at the M06-2X/6-311++G(d,p) level. The majority of the bond cleavages are homolytic via β-scission. Their energy barriers depend largely on the ability of the radical being stabilized in the transition structures and the availability of a mobile proton in the vicinity of the β-radical center. The N–Cα bond is less favorably cleaved than the Cα–C bond (except Ser and Thr) for systems without a mobile proton. It is because, firstly, the homolytic cleavage is less favorable for the more polar N–Cα bond than for the less polar Cα–C bond. Secondly, a less stable σ-radical localized on the amide nitrogen atom of the incipient N-terminal fragment is formed for the former, while a more stable radical delocalized in a π*(CO)-like orbital of the incipient C-terminal fragment is formed for the latter. In the presence of a mobile proton N-terminal to the β-radical center, some degrees of heterolytic cleavage character, as preferred by the polar N–Cα bond, are observed. Consequently, its barrier is reduced. If the mobile proton is located at the C-terminal amide oxygen of the β-radical center, the Cα–C bond cleavage will be significantly suppressed. It is because the radical in the incipient C-terminal fragment becomes more localized as a σ-radical on the carbon atom of its protonated amide group. With basic amino acid residues, the Cα–C bond cleavage can be reactivated. Heterolytic cleavage of the polar N–Cα bond can be largely facilitated if a mobile proton N-terminal to the β-radical center is available and the radical in the incipient C-terminal fragment is sufficiently stabilized, for instance, by the aromatic side chain of Trp and Tyr. Therefore, cleavages of the N–Cα bond induced by the β-radical tautomer of Trp and Tyr are often preferred as compared with cleavages of the Cα–C bond in peptide radical cations containing mobile protons.
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Affiliation(s)
- Wai-Kit Tang
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
| | - Chun-Ping Leong
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
| | - Qiang Hao
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
| | - Chi-Kit Siu
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
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7
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Piatkivskyi A, Happ M, Lau JKC, Siu KWM, Hopkinson AC, Ryzhov V. Investigation of Fragmentation of Tryptophan Nitrogen Radical Cation. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2015; 26:1388-1393. [PMID: 25962366 DOI: 10.1007/s13361-015-1134-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2015] [Accepted: 03/10/2015] [Indexed: 06/04/2023]
Abstract
This work describes investigation of the fragmentation mechanism of tryptophan N-indolyl radical cation, H3N(+)-TrpN(•) (m/z 204) studied via DFT calculations and several gas-phase experimental techniques. The main fragment ion at m/z 131, shown to be a mixture of up to four isomers including 3-methylindole (3MI) π-radical cation, was found to undergo further loss of an H atom to yield one of the two isomeric m/z 130 ions. 3-Methylindole radical cation generated independently (via CID of [Cu(II)(terpy)3MI](•2+)) displayed gas-phase reactivity partially similar to that of the m/z 131 fragment, further confirming our proposed mechanism. CID of deuterated tryptophan N-indolyl radical cation (m/z 208) suggested that up to six H atoms are involved in the pathway to formation of the m/z 131 ion, consistent with hydrogen atom scrambling during CID of protonated Trp.
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Affiliation(s)
- Andrii Piatkivskyi
- Department of Chemistry and Biochemistry, and Center for Biochemical and Biophysical Studies, Northern Illinois University, DeKalb, IL, 60115, USA
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8
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Williams D, Lau JKC, Zhao J, Mädler S, Wang Y, Saminathan IS, Hopkinson AC, Siu KWM. Radical-induced, proton-transfer-driven fragmentations in [b(5)-H]˙(+) ions derived from pentaalanyl tryptophan. Phys Chem Chem Phys 2015; 17:10699-707. [PMID: 25811808 DOI: 10.1039/c5cp00178a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The collision-induced dissociation (CID) of [b5 - H]˙(+) ions containing four alanine residues and one tryptophan give identical spectra regardless of the initial location of the tryptophan indicating that, as proposed for b5(+) ions, sequence scrambling occurs prior to dissociation. Cleavage occurs predominantly at the peptide bonds and at the N-Cα bond of the alanine residue that is attached to the N-terminus of the tryptophan residue. The product of the latter pathway, an ion at m/z 240, is the base peak in all the mass spectra. With the exception of one minor channel giving a b3(+) ion, the product ions retain both the tryptophan residue and the radical. Experiments with one trideuterated alanine established the sequences of loss of alanine residues. Formation of identical products implies a common intermediate, a [b5 - H]˙(+) ion that has a 'linear' structure in which the tryptophan residue is present as an α-radical located in the oxazolone ring, structure Ie. Density functional theory calculations show this structure to be at the global minimum, 14.6 kcal mol(-1) below the macrocyclic structure, ion II. Loss of CO from the [b5 - H]˙(+) ions is inhibited by the presence of the radical centre in the oxazolone ring and migration of the proton from the oxazolone ring onto the peptide backbone induces cleavage of an N-Cα or peptide bond. Three calculated structures for the ion at m/z 240 all have an oxazolone ring. Two of these structures may be formed from Ie, depending upon which proton migrates onto the peptide chain prior to the dissociation. The barrier to interconversion between these two structures requires a 1,3-hydrogen atom shift and is high (51.0 kcal mol(-1)), but both can convert into a third isomer that readily loses CO2 (barrier 38.7 kcal mol(-1)). The lowest barrier to the loss of CO, the usual fragmentation path observed for protonated oxazolones, is 47.0 kcal mol(-1).
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Affiliation(s)
- Declan Williams
- Department of Chemistry and Centre for Research in Mass Spectrometry, York University, 4700 Keele Street, Toronto, Ontario M3J 1P3, Canada
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9
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Oh HB, Moon B. Radical-driven peptide backbone dissociation tandem mass spectrometry. MASS SPECTROMETRY REVIEWS 2015; 34:116-132. [PMID: 24863492 DOI: 10.1002/mas.21426] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2012] [Revised: 05/06/2013] [Accepted: 11/20/2013] [Indexed: 06/03/2023]
Abstract
In recent years, a number of novel tandem mass spectrometry approaches utilizing radical-driven peptide gas-phase fragmentation chemistry have been developed. These approaches show a peptide fragmentation pattern quite different from that of collision-induced dissociation (CID). The peptide fragmentation features of these approaches share some in common with electron capture dissociation (ECD) or electron transfer dissociation (ETD) without the use of sophisticated equipment such as a Fourier-transform mass spectrometer. For example, Siu and coworkers showed that CID of transition metal (ligand)-peptide ternary complexes led to the formation of peptide radical ions through dissociative electron transfer (Chu et al., 2000. J Phys Chem B 104:3393-3397). The subsequent collisional activation of the generated radical ions resulted in a number of characteristic product ions, including a, c, x, z-type fragments and notable side-chain losses. Another example is the free radical initiated peptide sequencing (FRIPS) approach, in which Porter et al. and Beauchamp et al. independently introduced a free radical initiator to the primary amine group of the lysine side chain or N-terminus of peptides (Masterson et al., 2004. J Am Chem Soc 126:720-721; Hodyss et al., 2005 J Am Chem Soc 127: 12436-12437). Photodetachment of gaseous multiply charged peptide anions (Joly et al., 2008. J Am Chem Soc 130:13832-13833) and UV photodissociation of photolabile radical precursors including a C-I bond (Ly & Julian, 2008. J Am Chem Soc 130:351-358; Ly & Julian, 2009. J Am Soc Mass Spectrom 20:1148-1158) also provide another route to generate radical ions. In this review, we provide a brief summary of recent results obtained through the radical-driven peptide backbone dissociation tandem mass spectrometry approach.
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Affiliation(s)
- Han Bin Oh
- Department of Chemistry, Sogang University, Seoul, 121-742, Republic of Korea
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10
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Mu X, Song T, Xu M, Lai CK, Siu CK, Laskin J, Chu IK. Discovery and mechanistic studies of facile N-terminal Cα-C bond cleavages in the dissociation of tyrosine-containing peptide radical cations. J Phys Chem B 2014; 118:4273-81. [PMID: 24678922 DOI: 10.1021/jp410525f] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Fascinating N-terminal Cα-C bond cleavages in a series of nonbasic tyrosine-containing peptide radical cations have been observed under low-energy collision-induced dissociation (CID), leading to the generation of rarely observed x-type radical fragments, with significant abundances. CID experiments of the radical cations of the alanyltyrosylglycine tripeptide and its analogues suggested that the N-terminal Cα-C bond cleavage, yielding its [x2 + H](•+) radical cation, does not involve an N-terminal α-carbon-centered radical. Theoretical examination of a prototypical radical cation of the alanyltyrosine dipeptide, using density functional theory calculations, suggested that direct N-terminal Cα-C bond cleavage could produce an ion-molecule complex formed between the incipient a1(+) and x1(•) fragments. Subsequent proton transfer from the iminium nitrogen atom in a1(+) to the acyl carbon atom in x1(•) results in the observable [x1 + H](•+). The barriers against this novel Cα-C bond cleavage and the competitive N-Cα bond cleavage, forming the complementary [c1 + 2H](+)/[z1 - H](•+) ion pair, are similar (ca. 16 kcal mol(-1)). Rice-Ramsperger-Kassel-Marcus modeling revealed that [x1 + H](•+) and [c1 + 2H](+) species are formed with comparable rates, in agreement with energy-resolved CID experiments for [AY](•+).
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Affiliation(s)
- Xiaoyan Mu
- Department of Chemistry, The University of Hong Kong , Hong Kong, China
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11
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Lai CK, Mu X, Hao Q, Hopkinson AC, Chu IK. Formation, isomerization, and dissociation of ε- and α-carbon-centered tyrosylglycylglycine radical cations. Phys Chem Chem Phys 2014; 16:24235-43. [DOI: 10.1039/c4cp03119a] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The CID spectra of [Yε˙GG]+ and [YGGα˙]+ are identical, showing that interconversion occurs prior to dissociation. For [Yε˙GG]+, [Yπ˙GG]+ and [YGα˙G]+, the dissociation products are all distinctly different, indicating that dissociation occurs more readily than isomerization.
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Affiliation(s)
- Cheuk-Kuen Lai
- Department of Chemistry
- The University of Hong Kong
- Hong Kong, China
| | - Xiaoyan Mu
- Department of Chemistry
- The University of Hong Kong
- Hong Kong, China
| | - Qiang Hao
- Department of Chemistry
- The University of Hong Kong
- Hong Kong, China
| | - Alan C. Hopkinson
- Department of Chemistry and Centre for Research in Mass Spectrometry
- York University
- Toronto, Canada
| | - Ivan K. Chu
- Department of Chemistry
- The University of Hong Kong
- Hong Kong, China
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12
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Lee J, Park H, Kwon H, Kwon G, Jeon A, Kim HI, Sung BJ, Moon B, Oh HB. One-Step Peptide Backbone Dissociations in Negative-Ion Free Radical Initiated Peptide Sequencing Mass Spectrometry. Anal Chem 2013; 85:7044-51. [DOI: 10.1021/ac303517h] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- Jihye Lee
- Department
of Chemistry, Sogang University, Seoul
121-742, Korea
| | - Hyeyeon Park
- Department
of Chemistry, Sogang University, Seoul
121-742, Korea
| | - Hyuksu Kwon
- Department
of Chemistry, Sogang University, Seoul
121-742, Korea
| | - Gyemin Kwon
- Department
of Chemistry, Sogang University, Seoul
121-742, Korea
| | - Aeran Jeon
- Department
of Chemistry, Sogang University, Seoul
121-742, Korea
| | - Hugh I. Kim
- Department
of Chemistry, Pohang University of Science and Technology, Pohang
790-784, Korea
| | - Bong June Sung
- Department
of Chemistry, Sogang University, Seoul
121-742, Korea
| | - Bongjin Moon
- Department
of Chemistry, Sogang University, Seoul
121-742, Korea
| | - Han Bin Oh
- Department
of Chemistry, Sogang University, Seoul
121-742, Korea
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Lai CK, Ng DCM, Pang HF, Le Blanc JCY, Hager JW, Fang DC, Cheung ASC, Chu IK. Laser-induced dissociation of singly protonated peptides at 193 and 266 nm within a hybrid linear ion trap mass spectrometer. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2013; 27:1119-27. [PMID: 23592116 DOI: 10.1002/rcm.6545] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2012] [Revised: 02/08/2013] [Accepted: 02/13/2013] [Indexed: 05/16/2023]
Abstract
RATIONALE We implemented, for the first time, laser-induced dissociation (LID) within a modified hybrid linear ion trap mass spectrometer, QTrap, while preserving the original scanning capabilities and routine performance of the instrument. METHODS Precursor ions of interest were mass-selected in the first quadrupole (Q1), trapped in the radiofrequency-only quadrupole (q2), photodissociated under irradiation with a 193- or 266-nm laser beam in the third quadrupole (q3), and mass-analyzed using the linear ion trap. RESULTS LID of singly charged protonated peptides revealed, in addition to conventional amide-bond cleavages, preferential fragmentation at Cα -C/N-Cα bonds of the backbone as well as at the Cα -Cβ /Cβ -Cγ bonds of the side-chains. The LID spectra of [M+H](+) featured product ions that were very similar to the observed radical-induced fragmentations in the CID spectra of analogous odd-electron radical cations generated through dissociative electron-transfer in metal-ligand-peptide complexes or through laser photolysis of iodopeptides. CONCLUSIONS LID of [M+H](+) ions results in fragmentation channels that are comparable with those observed upon the CID of M(•+) ions, with a range of fascinating radical-induced fragmentations.
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Affiliation(s)
- Cheuk-Kuen Lai
- Department of Chemistry, The University of Hong Kong, Hong Kong, China
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14
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Affiliation(s)
- František Tureček
- Department of Chemistry, Bagley Hall, University of Washington , Seattle, Washington 98195-1700, United States
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15
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Love CB, Tan L, Francisco JS, Xia Y. Competition of Charge- versus Radical-Directed Fragmentation of Gas-Phase Protonated Cysteine Sulfinyl Radicals. J Am Chem Soc 2013; 135:6226-33. [PMID: 23527556 DOI: 10.1021/ja4008744] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Chasity B. Love
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084,
United States
| | - Lei Tan
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084,
United States
| | - Joseph S. Francisco
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084,
United States
| | - Yu Xia
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084,
United States
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16
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Piatkivskyi A, Osburn S, Jaderberg K, Grzetic J, Steill JD, Oomens J, Zhao J, Lau JKC, Verkerk UH, Hopkinson AC, Siu KWM, Ryzhov V. Structure and reactivity of the distonic and aromatic radical cations of tryptophan. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2013; 24:513-523. [PMID: 23512424 DOI: 10.1007/s13361-013-0594-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/02/2012] [Revised: 01/24/2013] [Accepted: 01/30/2013] [Indexed: 06/01/2023]
Abstract
In this work, we regiospecifically generate and compare the gas-phase properties of two isomeric forms of tryptophan radical cations-a distonic indolyl N-radical (H3N(+) - TrpN(•)) and a canonical aromatic π (Trp(•+)) radical cation. The distonic radical cation was generated by nitrosylating the indole nitrogen of tryptophan in solution followed by collision-induced dissociation (CID) of the resulting protonated N-nitroso tryptophan. The π-radical cation was produced via CID of the ternary [Cu(II)(terpy)(Trp)](•2+) complex. CID spectra of the two isomeric species were found to be very different, suggesting no interconversion between the isomers. In gas-phase ion-molecule reactions, the distonic radical cation was unreactive towards n-propylsulfide, whereas the π radical cation reacted by hydrogen atom abstraction. DFT calculations revealed that the distonic indolyl radical cation is about 82 kJ/mol higher in energy than the π radical cation of tryptophan. The low reactivity of the distonic nitrogen radical cation was explained by spin delocalization of the radical over the aromatic ring and the remote, localized charge (at the amino nitrogen). The lack of interconversion between the isomers under both trapping and CID conditions was explained by the high rearrangement barrier of ca.137 kJ/mol. Finally, the two isomers were characterized by infrared multiple-photon dissociation (IRMPD) spectroscopy in the ~1000-1800 cm(-1) region. It was found that some of the main experimental IR features overlap between the two species, making their distinction by IRMPD spectroscopy in this region problematic. In addition, DFT theoretical calculations showed that the IR spectra are strongly conformation-dependent.
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Affiliation(s)
- Andrii Piatkivskyi
- Department of Chemistry and Biochemistry, and Center for Biochemical and Biophysical Studies, Northern Illinois University, DeKalb, IL 60115, USA
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17
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Lau JKC, Lo S, Zhao J, Siu KWM, Hopkinson AC. Fragmentation chemistry of [Met-Gly]•+, [Gly-Met]•+, and [Met-Met]•+ radical cations. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2013; 24:543-553. [PMID: 23440718 DOI: 10.1007/s13361-013-0581-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2012] [Accepted: 01/04/2013] [Indexed: 06/01/2023]
Abstract
Radical cations [Met-Gly](•+), [Gly-Met](•+), and [Met-Met](•+) have been generated through collision-induced dissociation (CID) of [Cu(II)(CH3CN)2(peptide)](•2+) complexes. Their fragmentation patterns and dissociation mechanisms have been studied both experimentally and theoretically using density functional theory at the UB3LYP/6-311++G(d,p) level. The captodative structure, in which the radical is located at the α-carbon of the N-terminal residue and the proton is on the amide oxygen, is the lowest energy structure on each potential energy surface. The canonical structure, with the charge and spin both located on the sulfur, and the distonic ion with the proton on the terminal amino group, and the radical on the α-carbon of the C-terminal residue have similar energies. Interconversion between the canonical structures and the captodative isomers is facile and occurs prior to fragmentation. However, isomerization to produce the distonic structure is energetically less favorable and cannot compete with dissociation except in the case of [Gly-Met](•+). Charge-driven dissociations result in formation of [b(n) - H](•+) and a(1) ions. Radical-driven dissociation leads to the loss of the side chain of methionine as CH3-S-CH=CH2 producing α-glycyl radicals from both [Gly-Met](•+) and [Met-Met](•+). For [Met-Met](•+), loss of the side chain occurs at the C-terminal as shown by both labeling experiments and computations. The product, the distonic ion of [Met-Gly](•+), NH3 (+)CH(CH2CH2SCH3)CONHCH(•)COOH dissociates by loss of CH3S(•). The isomeric distonic ion NH3 (+)CH2CONHC(•)(CH2CH2SCH3)COOH is accessible directly from the canonical [Gly-Met](•+) ion. A fragmentation pathway that characterizes this ion (and the distonic ion of [Met-Met](•+)) is homolytic fission of the Cβ-Cγ bond to lose CH3SCH2(•).
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Affiliation(s)
- Justin Kai-Chi Lau
- Department of Chemistry and Centre for Research in Mass Spectrometry, York University, Toronto, ON, Canada
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18
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Zhang X, Julian RR. Exploring radical migration pathways in peptides with positional isomers, deuterium labeling, and molecular dynamics simulations. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2013; 24:524-533. [PMID: 23361370 DOI: 10.1007/s13361-012-0540-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2012] [Revised: 11/08/2012] [Accepted: 11/09/2012] [Indexed: 06/01/2023]
Abstract
One of the keys for understanding radical directed dissociation in peptides is a detailed knowledge of the factors that mediate radical migration. Peptide radicals can be created by a variety of means; however, in most circumstances, the originally created radicals must migrate to alternate locations in order to facilitate fragmentation such as backbone cleavage or side chain loss. The kinetics of radical migration are examined herein by comparing results from ortho-, meta-, and para-benzoyl radical positional isomers for several peptides. Isomers of a constrained cyclic peptide generated by several orthogonal radical initiators are also probed as a function of charge state. Cumulatively, the results suggest that small changes in radical position can significantly impact radical migration, and overall structural flexibility of the peptide is also an important controlling factor. A particularly interesting pathway for the peptide RGYALG that is sensitive to ortho versus meta or para substitution was fully mapped out by a suite of deuterium labeled peptides. This data was then used to optimize parameters in molecular dynamics-based simulations, which were subsequently used to obtain further insight into the structural underpinnings that most strongly influence the kinetics of radical migration.
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Affiliation(s)
- Xing Zhang
- Department of Chemistry, University of California, Riverside, CA 92521, USA
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19
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Jones AW, Winn PJ, Cooper HJ. The radical ion chemistry of S-nitrosylated peptides. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2012; 23:2063-2074. [PMID: 23055078 DOI: 10.1007/s13361-012-0492-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2012] [Revised: 07/11/2012] [Accepted: 07/20/2012] [Indexed: 06/01/2023]
Abstract
The radical ion chemistry of a suite of S-nitrosopeptides has been investigated. Doubly and triply-protonated ions of peptides NYCGLPGEYWLGNDK, NYCGLPGEYWLGNDR, NYCGLPGERWLGNDR, NACGAPGEKWAGNDK, NYCGLPGEKYLGNDK, NYGLPGCEKWYGNDK and NYGLPGEKWYGCNDK were subjected to electron capture dissociation (ECD), and collision-induced dissociation (CID). The peptide sequences were selected such that the effect of the site of S-nitrosylation, the nature and position of the basic amino acid residues, and the nature of the other amino acid side chains, could be interrogated. The ECD mass spectra were dominated by a peak corresponding to loss of (•)NO from the charge-reduced precursor, which can be explained by a modified Utah-Washington mechanism. Some backbone fragmentation in which the nitrosyl modification was preserved was also observed in the ECD of some peptides. Molecular dynamics simulations of peptide ion structure suggest that the ECD behavior was dependent on the surface accessibility of the protonated residue. CID of the S-nitrosylated peptides resulted in homolysis of the S-N bond to form a long-lived radical with loss of (•)NO. The radical peptide ions were isolated and subjected to ECD and CID. ECD of the radical peptide ions provided an interesting comparison to ECD of the unmodified peptides. The dominant process was electron capture without further dissociation (ECnoD). CID of the radical peptide ions resulted in cysteine, leucine, and asparagine side chain losses, and radical-induced backbone fragmentation at tryptophan, tyrosine, and asparagine residues, in addition to charge-directed backbone fragmentation.
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Affiliation(s)
- Andrew W Jones
- School of Biosciences, College of Life and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom
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20
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Kong RPW, Quan Q, Hao Q, Lai CK, Siu CK, Chu IK. Formation and dissociation of phosphorylated peptide radical cations. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2012; 23:2094-2101. [PMID: 22968907 PMCID: PMC3514703 DOI: 10.1007/s13361-012-0479-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/03/2012] [Revised: 08/14/2012] [Accepted: 08/14/2012] [Indexed: 06/01/2023]
Abstract
In this study, we generated phosphoserine- and phosphothreonine-containing peptide radical cations through low-energy collision-induced dissociation (CID) of the ternary metal-ligand phosphorylated peptide complexes [Cu(II)(terpy)(p)M](·2+) and [Co(III)(salen)(p)M](·+) [(p)M: phosphorylated angiotensin III derivative; terpy: 2,2':6',2''-terpyridine; salen: N,N'-ethylenebis(salicylideneiminato)]. Subsequent CID of the phosphorylated peptide radical cations ((p)M(·+)) revealed fascinating gas-phase radical chemistry, yielding (1) charge-directed b- and y-type product ions, (2) radical-driven product ions through cleavages of peptide backbones and side chains, and (3) different degrees of formation of [M - H(3)PO(4)](·+) species through phosphate ester bond cleavage. The CID spectra of the (p)M(·+) species and their non-phosphorylated analogues featured fragment ions of similar sequence, suggesting that the phosphoryl group did not play a significant role in the fragmentation of the peptide backbone or side chain. The extent of neutral H(3)PO(4) loss was influenced by the peptide sequence and the initial sites of the charge and radical. A preliminary density functional theory study, at the B3LYP 6-311++G(d,p) level of theory, of the neutral loss of H(3)PO(4) from a prototypical model--N-acetylphosphorylserine methylamide--revealed several factors governing the elimination of neutral phosphoryl groups through charge- and radical-induced mechanisms.
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Affiliation(s)
- Ricky P. W. Kong
- Department of Chemistry, University of Hong Kong, Hong Kong, China
| | - Quan Quan
- Department of Chemistry, University of Hong Kong, Hong Kong, China
| | - Qiang Hao
- Department of Biology and Chemistry, City University of Hong Kong, Hong Kong, China
| | - Cheuk-Kuen Lai
- Department of Chemistry, University of Hong Kong, Hong Kong, China
| | - Chi-Kit Siu
- Department of Biology and Chemistry, City University of Hong Kong, Hong Kong, China
| | - Ivan K. Chu
- Department of Chemistry, University of Hong Kong, Hong Kong, China
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21
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Tan L, Xia Y. Gas-phase peptide sulfinyl radical ions: formation and unimolecular dissociation. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2012; 23:2011-2019. [PMID: 22911098 DOI: 10.1007/s13361-012-0465-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2012] [Revised: 07/27/2012] [Accepted: 07/31/2012] [Indexed: 06/01/2023]
Abstract
A variety of peptide sulfinyl radical (RSO•) ions with a well-defined radical site at the cysteine side chain were formed at atmospheric pressure (AP), sampled into a mass spectrometer, and investigated via collision-induced dissociation (CID). The radical ion formation was based on AP reactions between oxidative radicals and peptide ions containing single inter-chain disulfide bond or free thiol group generated from nanoelectrospray ionization (nanoESI). The radical induced reactions allowed large flexibility in forming peptide radical ions independent of ion polarity (protonated or deprotonated) or charge state (singly or multiply charged). More than 20 peptide sulfinyl radical ions in either positive or negative ion mode were subjected to low energy collisional activation on a triple-quadrupole/linear ion trap mass spectrometer. The competition between radical- and charge-directed fragmentation pathways was largely affected by the presence of mobile protons. For peptide sulfinyl radical ions with reduced proton mobility (i.e., singly protonated, containing basic amino acid residues), loss of 62 Da (CH(2)SO), a radical-initiated dissociation channel, was dominant. For systems with mobile protons, this channel was suppressed, while charge-directed amide bond cleavages were preferred. The polarity of charge was found to significantly alter the radical-initiated dissociation channels, which might be related to the difference in stability of the product ions in different ion charge polarities.
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Affiliation(s)
- Lei Tan
- Department of Chemistry, Purdue University, West Lafayette, IN 47907-2084, USA
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22
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Kalli A, Hess S. Electron capture dissociation of hydrogen-deficient peptide radical cations. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2012; 23:1729-1740. [PMID: 22855421 DOI: 10.1007/s13361-012-0433-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2012] [Revised: 06/05/2012] [Accepted: 06/12/2012] [Indexed: 06/01/2023]
Abstract
Hydrogen-deficient peptide radical cations exhibit fascinating gas phase chemistry, which is governed by radical driven dissociation and, in many cases, by a combination of radical and charge driven fragmentation. Here we examine electron capture dissociation (ECD) of doubly, [M + H](2+•), and triply, [M + 2H](3+•), charged hydrogen-deficient species, aiming to investigate the effect of a hydrogen-deficient radical site on the ECD outcome and characterize the dissociation pathways of hydrogen-deficient species in ECD. ECD of [M + H](2+•) and [M + 2H](3+•) precursor ions resulted in efficient electron capture by the hydrogen-deficient species. However, the intensities of c- and z-type product ions were reduced, compared with those observed for the even electron species, indicating suppression of N-C(α) backbone bond cleavages. We postulate that radical recombination occurs after the initial electron capture event leading to a stable even electron intermediate, which does not trigger N-C(α) bond dissociations. Although the intensities of c- and z-type product ions were reduced, the number of backbone bond cleavages remained largely unaffected between the ECD spectra of the even electron and hydrogen-deficient species. We hypothesize that a small ion population exist as a biradical, which can trigger N-C(α) bond cleavages. Alternatively, radical recombination and N-C(α) bond cleavages can be in competition, with radical recombination being the dominant pathway and N-C(α) cleavages occurring to a lesser degree. Formation of b- and y-type ions observed for two of the hydrogen-deficient peptides examined is also discussed.
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Affiliation(s)
- Anastasia Kalli
- Proteome Exploration Laboratory, Division of Biology, Beckman Institute, California Institute of Technology, Pasadena, 91125, USA
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23
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Song T, Ma CY, Chu IK, Siu CK, Laskin J. Mechanistic Examination of Cβ–Cγ Bond Cleavages of Tryptophan Residues during Dissociations of Molecular Peptide Radical Cations. J Phys Chem A 2012; 117:1059-68. [PMID: 22697598 DOI: 10.1021/jp303562e] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Tao Song
- Department
of Chemistry and ‡School of Biological Sciences, The University of Hong Kong, Hong Kong, China
| | - Ching-Yung Ma
- Department
of Chemistry and ‡School of Biological Sciences, The University of Hong Kong, Hong Kong, China
| | - Ivan K. Chu
- Department
of Chemistry and ‡School of Biological Sciences, The University of Hong Kong, Hong Kong, China
| | - Chi-Kit Siu
- Department
of Biology and Chemistry, City University of Hong Kong, Hong Kong,
China
| | - Julia Laskin
- Chemical
and Materials Sciences Division, Pacific Northwest National Laboratory, Richland, Washington
99354, United States
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24
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Hao Q, Song T, Ng DCM, Quan Q, Siu CK, Chu IK. Arginine-Facilitated Isomerization: Radical-Induced Dissociation of Aliphatic Radical Cationic Glycylarginyl(iso)leucine Tripeptides. J Phys Chem B 2012; 116:7627-34. [DOI: 10.1021/jp301882p] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Qiang Hao
- Department of Chemistry, The University of Hong Kong, Hong Kong, China
- Department
of Biology and Chemistry, City University of Hong Kong, Hong Kong, China
| | - Tao Song
- Department of Chemistry, The University of Hong Kong, Hong Kong, China
| | - Dominic C. M. Ng
- Department of Chemistry, The University of Hong Kong, Hong Kong, China
| | - Quan Quan
- Department of Chemistry, The University of Hong Kong, Hong Kong, China
| | - Chi-Kit Siu
- Department
of Biology and Chemistry, City University of Hong Kong, Hong Kong, China
| | - Ivan K. Chu
- Department of Chemistry, The University of Hong Kong, Hong Kong, China
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25
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Song T, Hao Q, Law CH, Siu CK, Chu IK. Novel Cβ-Cγ bond cleavages of tryptophan-containing peptide radical cations. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2012; 23:264-273. [PMID: 22135037 PMCID: PMC3264861 DOI: 10.1007/s13361-011-0295-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2011] [Revised: 10/24/2011] [Accepted: 10/29/2011] [Indexed: 05/31/2023]
Abstract
In this study, we observed unprecedented cleavages of the C(β)-C(γ) bonds of tryptophan residue side chains in a series of hydrogen-deficient tryptophan-containing peptide radical cations (M(•+)) during low-energy collision-induced dissociation (CID). We used CID experiments and theoretical density functional theory (DFT) calculations to study the mechanism of this bond cleavage, which forms [M - 116](+) ions. The formation of an α-carbon radical intermediate at the tryptophan residue for the subsequent C(β)-C(γ) bond cleavage is analogous to that occurring at leucine residues, producing the same product ions; this hypothesis was supported by the identical product ion spectra of [LGGGH - 43](+) and [WGGGH - 116](+), obtained from the CID of [LGGGH](•+) and [WGGGH](•+), respectively. Elimination of the neutral 116-Da radical requires inevitable dehydrogenation of the indole nitrogen atom, leaving the radical centered formally on the indole nitrogen atom ([Ind](•)-2), in agreement with the CID data for [WGGGH](•+) and [W(1-CH3)GGGH](•+); replacing the tryptophan residue with a 1-methyltryptophan residue results in a change of the base peak from that arising from a neutral radical loss (116 Da) to that arising from a molecule loss (131 Da), both originating from C(β)-C(γ) bond cleavage. Hydrogen atom transfer or proton transfer to the γ-carbon atom of the tryptophan residue weakens the C(β)-C(γ) bond and, therefore, decreases the dissociation energy barrier dramatically.
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Affiliation(s)
- Tao Song
- Department of Chemistry, The University of Hong Kong, Hong Kong, China
| | - Qiang Hao
- Department of Chemistry, The University of Hong Kong, Hong Kong, China
- Department of Biology and Chemistry, City University of Hong Kong, Hong Kong, China
| | - Chun-Hin Law
- Department of Chemistry, The University of Hong Kong, Hong Kong, China
| | - Chi-Kit Siu
- Department of Biology and Chemistry, City University of Hong Kong, Hong Kong, China
| | - Ivan K. Chu
- Department of Chemistry, The University of Hong Kong, Hong Kong, China
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26
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Zhao J, Song T, Xu M, Quan Q, Siu KWM, Hopkinson AC, Chu IK. Intramolecular hydrogen atom migration along the backbone of cationic and neutral radical tripeptides and subsequent radical-induced dissociations. Phys Chem Chem Phys 2012; 14:8723-31. [DOI: 10.1039/c2cp40708f] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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