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?CN 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. 相似文献
As a means of generating fixed-charge peptide radicals in the gas phase we have examined the collision-induced dissociation (CID) chemistry of ternary [Cu(II)(terpy)(TMPP-M)]2+ complexes, where terpy = 2,2':6'2'-terpyridine and TMPP-M represents a peptide (M) modified by conversion of the N-terminal amine to a [tris(2,4,6-trimethoxyphenyl)phosphonium]acetamide (TMPP-) fixed-charge derivative. The following modified peptides were examined: oligoglycines, (Gly)n (n = 1-5), alanylglycine, glycylalanine, dialanine, trialanine and leucine-enkephaline (YGGFL). The [Cu(II)(terpy)(TMPP-M)]2+ complexes are readily formed upon electrospray ionization (ESI) of a mixture of derivatized peptide and [Cu(II)(terpy)(NO3)2] and generally fragment to form transient peptide radical cations, TMPP-M+*, which undergo rapid decarboxylation for the simple aliphatic peptides. This is contrasted with the complexes containing the unmodified peptides, which predominantly undergo fragmentation of the coordinated peptide. These differences demonstrate the importance of proton mobility in directing fragmentation of ternary copper(II) peptide complexes. In the case of leucine-enkephaline, a sufficient yield of the radical cation was obtained to allow further CID. The TMPP-YGGFL+* ion showed a rich fragmentation chemistry, including CO2 loss, side-chain losses of an isopropyl radical, 2-methylpropene and p-quinomethide, and *a1 and *a4 sequence ion formation. In contrast, the even-electron TMPP-YGGFL+ ion fragments to form *a(n) and *b(n) sequence ions as well as the [*b4 + H2O]+ rearrangement ion. 相似文献
Our previous study showed that selenamide reagents such as ebselen and N-(phenylseleno)phthalimide (NPSP) can be used for selective and rapid derivatization of protein/peptide thiols in high conversion
yield. This paper reports the systematic investigation of MS/MS dissociation behaviors of selenamide-derivatized peptide ions
upon collision induced dissociation (CID) and electron transfer dissociation (ETD). In the positive ion mode, derivatized
peptide ions exhibit tag-dependent CID dissociation pathways. For instance, ebselen-derivatized peptide ions preferentially
undergo Se–S bond cleavage upon CID to produce a characteristic fragment ion, the protonated ebselen (m/z 276), which allows selective identification of thiol peptides from protein digest as well as selective detection of thiol
proteins from protein mixture using precursor ion scan (PIS). In contrast, NPSP-derivatized peptide ions retain their phenylselenenyl
tags during CID, which is useful in sequencing peptides and locating cysteine residues. In the negative ion CID mode, both
types of tags are preferentially lost via the Se–S cleavage, analogous to the S–S bond cleavage during CID of disulfide-containing
peptide anions. In consideration of the convenience in preparing selenamide-derivatized peptides and the similarity of Se–S
of the tag to the S–S bond, we also examined ETD of the derivatized peptide ions to probe the mechanism for electron-based
ion dissociation. Interestingly, facile cleavage of Se–S bond occurs to the peptide ions carrying either protons or alkali
metal ions, while backbone cleavage to form c/z ions is severely inhibited. These results are in agreement with the Utah-Washington mechanism proposed for depicting electron-based
ion dissociation processes. 相似文献
Electron capture dissociation (ECD) studies of two modified amyloid beta peptides (20-29 and 25-35) were performed to investigate the role of H* radicals in the ECD of peptide ions and the free-radical cascade (FRC) mechanism. 2,4,6-Trimethylpyridinium (TMP) was used as the fixed charge tag, which is postulated to both trap the originally formed radical upon electron capture and inhibit the H* generation. It was found that both the number and locations of the fixed charge groups influenced the backbone and side-chain cleavages of these peptides in ECD. In general, the frequency and extent of backbone cleavages decreased and those of side-chain cleavages increased with the addition of fixed charge tags. A singly labeled peptide with the tag group farther away from the protonated site experienced a smaller abundance decrease in backbone cleavage fragments than the one with the tag group closer to the protonated site. Despite the nonprotonated nature of all charge carriers in doubly labeled peptide ions, several c and z* ions were still observed in their ECD spectra. Thus, although H* transfer may be important for the NC(alpha) bond cleavage, there also exist other pathways, which would require a radical migration via H* abstraction through space or via an amide superbase mechanism. Finally, internal fragment ions were observed in the ECD of these linear peptides, indicating that the important role of the FRC in backbone cleavages is not limited to the ECD of cyclic peptides. 相似文献
The number and types of diagnostic ions obtained by infrared multiphoton dissociation (IRMPD) and collision-induced dissociation
(CID) were evaluated for supercharged peptide ions created by electrospray ionization of solutions spiked with m-nitrobenzyl alcohol. IRMPD of supercharged peptide ions increased the sequence coverage compared with that obtained by CID
for all charge states investigated. The number of diagnostic ions increased with the charge state for IRMPD; however, this
trend was not consistent for CID because the supercharged ions did not always yield the greatest number of diagnostic ions.
Significantly different fragmentation pathways were observed for the different charge states upon CID or IRMPD with the latter
yielding far more immonium ions and often fewer uninformative ammonia, water, and phosphoric acid neutral losses. Pulsed-Q
dissociation resulted in an increase in the number of internal product ions, a decrease in sequence-informative ions, and
reduced overall ion abundances. The enhanced sequence coverage afforded by IRMPD of supercharged ions was demonstrated for
a variety of model peptides, as well as for a tryptic digest of cytochrome c. 相似文献
Electron capture dissociation (ECD) and collision-induced dissociation (CID), the two complementary fragmentation techniques, are demonstrated to be effective in the detection and localization of the methionine sulfoxide [Met(O)] residues in peptides using Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. The presence of Met(O) can be easily recognized in the low-energy CID spectrum showing the characteristic loss of methanesulfenic acid (CH(3)SOH, 64 Da) from the side chain of Met(O). The position of Met(O) can then be localized by ECD which is capable of providing extensive peptide backbone fragmentation without detaching the labile Met(O) side chain. We studied CID and ECD of several Met(O)-containing peptides that included the 44-residue human growth hormone-releasing factor (GRF) and the human atrial natriuretic peptide (ANP). The distinction and complementarity of the two fragmentation techniques were particularly remarkable in their effects on ANP, a disulfide bond-containing peptide. While the predominant fragmentation pathway in CID of ANP was the loss of CH(3)SOH (64 Da) from the molecular ion, ECD of ANP resulted in many sequence-informative products, including those from cleavages within the disulfide-bonded cyclic structure, to allow for the direct localization of Met(O) without the typical procedures for disulfide bond reduction followed by [bond]SH alkylation. 相似文献
Lasso peptides constitute a class of bioactive peptides sharing a knotted structure where the C-terminal tail of the peptide is threaded through and trapped within an N-terminal macrolactam ring. The structural characterization of lasso structures and differentiation from their unthreaded
topoisomers is not trivial and generally requires the use of complementary biochemical and spectroscopic methods. Here we
investigated two antimicrobial peptides belonging to the class II lasso peptide family and their corresponding unthreaded
topoisomers: microcin J25 (MccJ25), which is known to yield two-peptide product ions specific of the lasso structure under
collision-induced dissociation (CID), and capistruin, for which CID does not permit to unambiguously assign the lasso structure.
The two pairs of topoisomers were analyzed by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry
(ESI-FTICR MS) upon CID, infrared multiple photon dissociation (IRMPD), and electron capture dissociation (ECD). CID and ECD
spectra clearly permitted to differentiate MccJ25 from its non-lasso topoisomer MccJ25-Icm, while for capistruin, only ECD
was informative and showed different extent of hydrogen migration (formation of c•/z from c/z•) for the threaded and unthreaded topoisomers. The ECD spectra of the triply-charged MccJ25 and MccJ25-lcm showed a series
of radical b-type product ions ( b¢n · ) \left( {b{\prime}_n^{ \bullet }} \right) . We proposed that these ions are specific of cyclic-branched peptides and result from a dual c/z• and y/b dissociation, in
the ring and in the tail, respectively. This work shows the potentiality of ECD for structural characterization of peptide
topoisomers, as well as the effect of conformation on hydrogen migration subsequent to electron capture. 相似文献
This tutorial presents the most common ion activation techniques employed in tandem mass spectrometry. In-source fragmentation and metastable ion decompositions, as well as the general theory of unimolecular dissociations of ions, are initially discussed. This is followed by tandem mass spectrometry, which implies that the activation of ions is distinct from the ionization step, and that the precursor and product ions are both characterized independently by their mass/charge ratios. In collision-induced dissociation (CID), activation of the selected ions occurs by collision(s) with neutral gas molecules in a collision cell. This experiment can be done at high (keV) collision energies, using tandem sector and time-of-flight instruments, or at low (eV range) energies, in tandem quadrupole and ion trapping instruments. It can be performed using either single or multiple collisions with a selected gas and each of these factors influences the distribution of internal energy that the activated ion will possess. While CID remains the most common ion activation technique employed in analytical laboratories today, several new methods have become increasingly useful for specific applications. More recent techniques are examined and their differences, advantages and disadvantages are described in comparison with CID. Collisional activation upon impact of precursor ions on solid surfaces, surface-induced dissociation (SID), is gaining importance as an alternative to gas targets and has been implemented in several different types of mass spectrometers. Furthermore, unique fragmentation mechanisms of multiply-charged species can be studied by electron-capture dissociation (ECD). The ECD technique has been recognized as an efficient means to study non-covalent interactions and to gain sequence information in proteomics applications. Trapping instruments, such as quadrupole ion traps and Fourier transform ion cyclotron resonance instruments, are particularly useful for the photoactivation of ions, specifically for fragmentation of precursor ions by infrared multiphoton dissociation (IRMPD). IRMPD is a non-selective activation method and usually yields rich fragmentation spectra. Lastly, blackbody infrared radiative dissociation is presented with a focus on determining activation energies and other important parameters for the characterization of fragmentation pathways. The individual methods are presented so as to facilitate the understanding of each mechanism of activation and their particular advantages and representative applications. 相似文献
A radio frequency-free electromagnetostatic (EMS) cell devised for electron-capture dissociation (ECD) of ions has been retrofitted into the collision-induced dissociation (CID) section of a triple quadrupole mass spectrometer to enable recording of ECD product-ion mass spectra and simultaneous recording of ECD-CID product-ion mass spectra. This modified instrument can be used to produce easily interpretable ECD and ECD-CID product-ion mass spectra of tyrosine-phosphorylated peptides that cover over 50% of their respective amino-acid sequences and readily identify their respective sites of phosphorylation. ECD fragmentation of doubly protonated, tyrosine-phosphorylated peptides, which was difficult to observe with FT-ICR instruments, occurs efficiently in the EMS cell. Figure
The fragmentation behavior of nitrated and S-nitrosylated peptides were studied using collision induced dissociation (CID)
and metastable atom-activated dissociation mass spectrometry (MAD-MS). Various charge states, such as 1+, 2+, 3+, 2–, of modified
and unmodified peptides were exposed to a beam of high kinetic energy helium (He) metastable atoms resulting in extensive
backbone fragmentation with significant retention of the post-translation modifications (PTMs). Whereas the high electron
affinity of the nitrotyrosine moiety quenches radical chemistry and fragmentation in electron capture dissociation (ECD) and
electron transfer dissociation (ETD), MAD does produce numerous backbone cleavages in the vicinity of the modification. Fragment
ions of nitrosylated cysteine modifications typically exhibit more abundant neutral losses than nitrated tyrosine modifications
because of the extremely labile nature of the nitrosylated cysteine residues. However, compared with CID, MAD produced between
66% and 86% more fragment ions, which preserved the labile –NO modification. MAD was also able to differentiate I/L residues
in the modified peptides. MAD is able to induce radical ion chemistry even in the presence of strong radical traps and therefore
offers unique advantages to ECD, ETD, and CID for determination of PTMs such as nitrated and S-nitrosylated peptides. 相似文献
The dissociation behavior of phosphorylated and sulfonated peptide anions was explored using metastable atom-activated dissociation
mass spectrometry (MAD-MS) and collision-induced dissociation (CID). A beam of high kinetic energy helium (He) metastable
atoms was exposed to isolated phosphorylated and sulfonated peptides in the 3– and 2– charge states. Unlike CID, where phosphate
losses are dominant, the major dissociation channels observed using MAD were Cα – C peptide backbone cleavages and neutral losses of CO2, H2O, and [CO2 + H2O] from the charge reduced (oxidized) product ion, consistent with an electron detachment dissociation (EDD) mechanism such
as Penning ionization. Regardless of charge state or modification, MAD provides ample backbone cleavages with little modification
loss, which allows for unambiguous PTM site determination. The relative abundance of certain fragment ions in MAD is also
demonstrated to be somewhat sensitive to the number and location of deprotonation sites, with backbone cleavage somewhat favored
adjacent to deprotonated sites like aspartic acid residues. MAD provides a complementary dissociation technique to CID, ECD,
ETD, and EDD for peptide sequencing and modification identification. MAD offers the unique ability to analyze highly acidic
peptides that contain few to no basic amino acids in either negative or positive ion mode. 相似文献
Electron capture dissociation (ECD) of a series of five residue peptides led to the observation that these small peptides
did not lead to the formation of the usual c/z ECD fragments, but to a, b, y, and w fragments. In order to determine how general this behavior is for small sized peptides, the effect of peptide size on ECD
fragments using a complete set of ECD spectra from the SwedECD spectra database was examined. Analysis of the database shows
that b and w fragments are favored for small peptide sizes and that average fragment size shows a linear relationship to parent peptide
size for most fragment types. From these data, it appears that most of the w fragments are not secondary fragments of the major z ions, in sharp contrast with the proposed mechanism leading to these ions. These data also show that c fragment distributions depend strongly on the nature of C-terminal residue basic site: arginine leads to loss of short neutral
fragments, whereas lysine leads to loss of longer neutral fragments. It also appears that b ions might be produced by two different mechanisms depending on the parent peptide size. A model for the fragmentation pathways
in competition is proposed. These relationships between average fragment size and parent peptide size could be further exploited
also for CID fragment spectra and could be included in fragmentation prediction algorithms. 相似文献
Charge tagging is a peptide derivatization process that commonly localizes a positive charge on the N-terminus. Upon low energy activation (e.g., collision-induced dissociation or post-source decay) of charge tagged peptides, relatively few fragment ions are produced due to the absence of mobile protons. In contrast, high energy fragmentation, such as 157 nm photodissociation, typically leads to a series of a-type ions. Disadvantages of existing charge tags are that they can produce mobile protons or that they are undesirably large and bulky. Here, we investigate a small triethylphosphonium charge tag with two different linkages: amide (158 Da) and amidine bonds (157 Da). Activation of peptides labeled with a triethylphosphonium charge tag through an amide bond can lead to loss of the charge tag and the production of protonated peptides. This enables low intensity fragment ions from both the protonated and charge tagged peptides to be observed. Triethylphosphonium charge tagged peptides linked through an amidine bond are more stable. Post-source decay and photodissociation yield product ions that primarily contain the charge tag. Certain amidine induced fragments are also observed. The previously reported tris(trimethoxyphenyl) phosphonium acetic acid N-hydroxysuccinimidyl ester charge tag shows a similar fragment ion distribution, but the mass of the triethylphosphonium tag label is 415 Da smaller.
Various peptide modifications have been explored recently to facilitate the acquisition of sequence information. N-terminal sulfonation is an interesting modification because it allows unambiguous de novo sequencing of peptides, especially in conjunction with MALDI-PSD-TOF analysis; such modified peptide ions undergo fragmentation at energies lower than those required conventionally for unmodified peptide ions. In this study, we systematically investigated the fragmentation mechanisms of N-terminal sulfonated peptide ions prepared using two different N-terminal sulfonation reagents: 4-sulfophenyl isothiocyanate (SPITC) and 4-chlorosulfophenyl isocyanate (SPC). Collision-induced dissociation (CID) of the SPC-modified peptide ions produced a set of y-series ions that were more evenly distributed relative to those observed for the SPITC-modified peptides; y(n-1) ion peaks were consistently and significantly larger than the signals of the other y-ions. We experimentally investigated the differences between the dissociation energies of the SPITC- and SPC-modified peptide ions by comparing the MS/MS spectra of the complexes formed between the crown ether 18-crown-6 (CE) and the modified peptides. Upon CID, the complexes formed between 18-crown-6 ether and the protonated amino groups of C-terminal lysine residues underwent either peptide backbone fragmentation or complex dissociation. Although the crown ether complexes of the unmodified ([M + CE + 2H]2+) and SPC-modified ([M* + CE + 2H]2+) peptides underwent predominantly noncovalent complex dissociation upon CID, the low-energy dissociations of the crown ether complexes of the SPITC-modified peptides ([M' + CE + 2H]2+) unexpectedly resulted in peptide backbone fragmentations, along with a degree of complex dissociation. We performed quantum mechanical calculations to address the energetics of fragmentations observed for the modified peptides. 相似文献
Electron capture dissociation (ECD) has become an alternative method to collision-activated dissociation (CAD) to avoid gas-phase cleavage of post-translational modifications carried by side chains from the peptide backbone. Nonetheless, as illustrated herein by the study of O-glycosylated and O-phosphorylated peptides, the extent of ECD fragmentations may be insufficient to cover the entire peptide sequence and to localize accurately these modifications. The present work demonstrates that the derivatization of peptides at their N-terminus by a phosphonium group improves dramatically and systematically the sequence coverage deduced from the ECD spectrum for both O-glycosylated and O-phosphorylated peptides compared with their native counterparts. The exclusive presence of N-terminal fragments (c-type ions) in the ECD spectra of doubly charged molecular cations simplifies peptide sequence interpretation. Thus, the combination of ECD and fixed charge derivatization appears as an efficient analytical tool for the extensive sequencing of peptides bearing labile groups. 相似文献