Specific photodissociation of peptides with multi‐stage mass spectrometry

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A set of three heparin-derived disaccharide deprotonated ions was isolated in a linear ion trap and subjected to UV laser irradiation in the 220 -290 nm wavelength range. The dissociation yields of the deprotonated molecular ions were recorded as a function of laser wavelength. They revealed maximum absorption at 220 nm for the nonsulfated disaccharide, but centered at 240 nm for the sulfated species. The comparison of the fragmentation patterns between ultraviolet photodissociation (UVPD) at 240 nm and CID modes showed roughly the same distribution of fragment ions resulting from glycosidic bond cleavages. Interestingly, UVPD favored additional cross ring cleavages of A and X type ion series enabling easier sulfate group location. It also reduced small neutral losses ( T he major advances achieved in mass spectrometry have revolutionized the structural analysis of proteins and led to the emergence of proteomic strategies. Although software-assisted de novo sequencing of peptides resulting from unknown proteins has become a routine task, the structural assignment of complex N-and O-glycans is much less trivial. Unlike proteins accurately translated from a unique template that follows a universal code, a similar set of glycosyl transferases may, across different species, build oligosaccharides of different structure according to an a priori unpredictable chronological catalysis activity.Compared with N-and O-linked glycans, the issue of structural complexity is continuing to increase in the world of glycosaminoglycans. Glycosaminoglycans are linear polymerized disaccharidic repeating units containing hexuronic acids and hexosamines. Their essential roles in governing numerous biologic functions [1] have led many groups to focus their efforts on defining generic strategies based on mass spectrometry, to obtain the structural definition of these acidic oligosaccharides. In the case of oligosaccharides derived from heparin or heparane sulfate, both glucuronic and iduronic acids and glucosamine may be sulfated at their OH and NH 2 groups. The fragmentation behavior of heparin-derived oligosaccharides has proven to be difficult to predict. Sulfate groups often impede access to exhaustive structural information by collision induced dissociation (CID)-MS/MS. Indeed, when the charge state of the selected molecular ion is low, neutral SO 3 losses most often predominate in comparison with glycosidic backbone cleavages [2]. This situation can be improved by combining MS/MS data resulting from different charge states.Very recently, Amster and coworkers published outstanding results showing how promising the electron detachment dissociation (EDD) of deprotonated sulfated oligosaccharides can be in providing informative fragment ions [3]. In particular, they documented the discrimination between the C5 epimeric glucuronic and iduronic acids based on specific fragment ions [4]. As in CID mode, they also observed that SO 3 loss can be dramatically reduced when EDD is performed on the charge states where the carboxylate group is ...

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Wavelength-tunable ultraviolet photodissociation (UVPD) of heparin-derived disaccharides in a linear ion trap

Racaud

Antoine

Joly

et al. 2009

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“…After excitation, direct dissociation in excited states competes with internal conversion to the electronic ground state and with radiative de-excitation. In particular, in UVPD, specific fragmentation channels are detected, namely formation of radical cations following a hydrogen atom loss and C α -C β bond cleavage fragments [4,5]. The above mentioned UV excitations rely on the existence of aromatic amino acids in the peptide sequence.…”

Section: Introductionmentioning

confidence: 99%

Formation and Fragmentation of Radical Peptide Anions: Insights from Vacuum Ultra Violet Spectroscopy

Brunet

Antoine

Dugourd

et al. 2011

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We have studied the photodissociation of gas-phase deprotonated caerulein anions by vacuum ultraviolet (VUV) photons in the 4.5 to 20 eV range, as provided by the DESIRS beamline at the synchrotron radiation facility SOLEIL (France). Caerulein is a sulphated peptide with three aromatic residues and nine amide bonds. Electron loss is found to be the major relaxation channel at every photon energy. However, an increase in the fragmentation efficiency (neutral losses and peptide backbone cleavages) as a function of the energy is also observed. The oxidized ions, generated by electron photodetachment were further isolated and activated by collision (CID) in a MS 3 scheme. The branching ratios of the different fragments observed by CID as a function of the initial VUV photon energy are found to be independent of the initial photon energy. Thus, there is no memory effect of the initial excitation energy on the fragmentation channels of the oxidized species on the time scale of our tandem MS experiment. We also report photofragment yields as a function of photon energy for doubly deprotonated caerulein ions, for both closed-shell ([M -2H] 2-) non-radical ions and open-shell ([M -3H] 2-• ) radical ions. These latter ions are generated by electron photodetachment from [M -3H] 3-precursor ions. The detachment yield increases monotonically with the energy with the appearance of several absorption bands. Spectra for radical and non-radical ions are quite similar in terms of observed bands; however, the VUV fragmentation yield is enhanced by the presence of a radical in caerulein peptides.

“…Successful photodissociation of peptides has been demonstrated using a CO 2 laser (10.6 μm, 0.1 eV per photon) [8,[17][18][19], an F 2 excimer laser (157 nm, 7.9 eV per photon) [20][21][22], an ArF excimer (193 nm, 6.4 eV per photon) [23,24], a Nd:YAG laser (266 nm, 4.7 eV per photon or 355 nm, 3.5 eV per photon) [25][26][27][28][29][30][31][32], and a femtosecond titanium sapphire laser (800 nm, 1.5 eV per photon) [33]. For example, Reilly et al reported the UVPD of peptides that involved 157 nm photodissociation with an F 2 excimer laser [20].…”

Section: Introductionmentioning

confidence: 99%

Ultraviolet Photodissociation of Carboxylate-Derivatized Peptides in a Quadrupole Ion Trap

Brodbelt

2011

The fragmentation patterns obtained by ultraviolet photodissociation (UVPD) and collisioninduced dissociation (CID) in a quadrupole ion trap mass spectrometer were compared for peptides modified at their C-termini and at acidic amino acids. Attachment of Alexa Fluor 350 or 7-amino-4-methyl-coumarin chromophores at the C-terminal and acidic residues enhances the UV absorptivity of the peptides and all fragment ions that retain the chromophore, such as the y ions that contain the chromophore-modified C-terminus. Whereas CID results in the formation of the typical array of mainly y-type and a/b-type fragment ions, UVPD produces predominantly a/ b-type ions with greatly reduced abundances of y ions. Immonium ions, mostly ones from aromatic or basic amino acids, are also observed in the low m/z range upon UVPD. UVPD of peptides containing two chromophore moieties (with one at the C-terminus and another at an acidic residue) results in even more efficient photodissociation at the expense of the annihilation of almost all diagnostic b and y ions containing the chromophore.