Conservation of mechanism in three chorismate-utilizing enzymes

Chorismate is the end-product of the shikimate pathway for biosynthesis of carbocyclic aromatic compounds in plants, bacteria, fungi, and some parasites. Anthranilate synthase (AS), 4-amino-4-deoxychorismate synthase (ADCS), and isochorismate synthase (IS) are homologous enzymes that carry out the initial transformations on chorismate in the biosynthesis of tryptophan, p-aminobenzoate, and enterobactin, respectively, and are expected to share a common mechanism. Poor binding to ADCS of two potential transition state analogues for addition of a nucleophile to C6 of chorismate implies that it, like AS and IS, initiates reaction by addition of a nucleophile to C2. Molecular modeling based on the X-ray structures of AS and ADCS suggests that the active site residue K274 is the nucleophile employed by ADCS to initiate the reaction, forming a covalent intermediate. The K274A and K274R mutants were shown to have 265- and 640-fold reduced k(cat) values when PabA (the cognate amidotransferase) + glutamine are used as the nitrogen source. Under conditions of saturating chorismate and NH(4)(+), ADCS and the K274A mutant have identical k(cat) values, suggesting the participation of NH(4)(+) as a rescue agent. Such participation was confirmed by the buildup of 2-amino-2-deoxyisochorismate in the reactions of the K274A mutant but not ADCS, when either NH(4)(+) or PabA + glutamine is used as the nitrogen source. Additionally, the inclusion of ethylamine in the reactions of K274A yields the N-ethyl derivative of 2-amino-2-deoxyisochorismate. A unifying mechanism for AS, ADCS, and IS entailing nucleophile addition to C2 of chorismate in an S(N)2' ' process is proposed.     

Electrospray mass spectrometry in the clinical diagnosis of variant hemoglobins

A combination of mass spectrometric (MS) techniques [electrospray MS, liquid secondary ion MS (LSIMS) and MS-MS] has been used for variant hemoglobin (Hb) detection and characterization. Electrospray MS allowed analysis of mixtures of intact globins giving simultaneously the molecular weights (accuracy 1-2 Da) and information about relative amounts of globins present. Currently, 14 Da is the minimum molecular weight difference required experimentally to accurately measure different species present in a mixture of 15-16 kDa proteins. Thus 80 and 79% of the known variants of alpha and beta chains, respectively, can be detected in mixtures with their normal counterparts, including Hb S (molecular weight difference = 30 Da). Abnormal hemoglobins detected were fractionated by C4 reversed-phase high-performance liquid chromatography (HPLC), and the separated globin chains (or the mixture of whole precipitated globin) were digested by trypsin. The tryptic peptides were separated by C18 reversed-phase HPLC and analyzed by LSIMS to narrow down the mutation site to a single peptide. The mass measured in LSIMS frequently corresponded to a unique structure, thus giving the unequivocal identification of the mutation and its site. Where there was ambiguity, tandem MS on a Kratos Concept four-sector instrument was used for sequencing the abnormal peptide. The practical use of the methodologies presented is illustrated through analysis and identification of Hb G-San Jose, Hb Stanleyville II, Hb S and Hb Willamette.     

Selective detection of thiosulfate-containing peptides using tandem mass spectrometry

Incubation of proteins or peptides containing disulfide bonds (S-S) with sodium sulfite (Na(2)SO(3)) cleaves S-S bonds producing approximately equimolar amounts of free thiols (-SH) and thiosulfates (-S-SO(3)H), a process known as sulfitolysis. Proteins and peptides containing thiosulfates were separated by reverse-phase high-performance liquid chromatography (RP-HPLC) and characterized by mass spectrometry (MS) and peptide mapping. The mass of the thiosulfate-containing peptide formed from oxidized insulin B chain was 3478.02 Da, 80 Da greater than the reduced peptide and corresponding precisely to addition of sulfur trioxide (SO(3)). Disulfide bond cleavage was also observed using RP-HPLC and MS after incubation of the intramolecular homodimer of mouse S100A8 (mass 20614 Da). The mass of HPLC-separated A8-SH was 10308 Da, and 10388 Da for A8-S-SO(3)H. Loss of SO(3) from multiply charged precursor ions was generally observed at elevated declustering potentials in the source region or within q(2) at relatively low collision energies (approximately 20 V). The characteristic loss of SO(3) at low collision energies preceded peptide backbone fragmentations at higher collision energies. Accurate mass measurement and charge-state discrimination, using a hybrid quadrupole time-of-flight mass spectrometer, allowed specific detection of thiosulfate-containing peptides. An information-dependent acquisition method, where the switch criterion was loss of m/z 79.9568, specifically identified 11 thiosulfate-containing peptides using nano-LC/MS from a tryptic digest of bovine serum albumin (BSA).     

Investigation of apparent mass deviations in electrospray ionization tandem mass spectrometry of a benzophenone-labeled peptide

In a previous study utilizing benzophenone-based topological probes to study conformationally dependent changes in mouse muscle nicotinic acetylcholine receptor (nAChR) topology, electrospray ionization tandem mass spectrometric (ESI-MS/MS) analysis led to a consistent -2.0 Da mass deviation from expected values. In the present study a synthetic peptide, corresponding to nAChR alpha1 subunit residues 130-139, was photolabeled. MS/MS analysis of this peptide using an ion trap confirmed the previously observed mass deviation, associated only with fragment ions that contain the incorporated benzophenone moiety. Analysis of peak profiles for the photolabeled ions does not indicate the typical 'peak fronting' that produces a mass shift when labile ions are prematurely ejected from the ion trap. Rather, hydrogen/deuterium (H/D) exchange experiments support the hypothesis that a chemical rearrangement involving phenyl migration and ketone formation has formed an unexpected oxidized peptide, with molecular mass 2 Da less than that expected, that is isolated for collision-induced dissociation in the ion trap together with the predicted precursor due to the broad ion isolation window specified.     

Investigation of tyrosine nitration and nitrosylation of angiotensin II and bovine serum albumin with electrospray ionization mass spectrometry

Protein tyrosine nitration is one of the important regulatory mechanisms in various cellular phenomena such as cell adhesion, endo/exo-cytosis of cellular materials, and signal transduction. In the present study, electrospray ionization tandem mass spectrometry (ESI-MS/MS) with a linear ion-trap mass spectrometer was applied for identification of nitrated proteins and localization of the modified tyrosine residues. When angiotensin II(DRVYIHPF) was nitrated in vitro with tetranitromethane (TNM), the mass spectrum showed a shift of +45 Da which corresponded to tyrosine nitration. An additional +29 Da mass shift was also detected by ESI-MS. This differed from nitrated peptide analysis with matrix-associated laser desorption/ionization mass spectrometry (MALDI-MS), which showed oxygen neutral loss from the nitrated tyrosine residues upon laser irradiation. Hence the +29 Da mass shift of the nitrated peptide observed by ESI-MS suggested the introduction of an NO group for nitrosylation of tyrosine residues. To confirm this in vitro nitrosylation on the protein level, bovine serum albumin was in vitro nitrated with TNM and analyzed by ESI-MS/MS. As expected, +29 as well as +45 Da mass shifts were detected, and the +29 Da mass shift was found to correspond to the modification on tyrosine residues by NO. Although the chemical mechanism by which this occurs in ESI-MS is not clear, the +29 Da mass shift could be a new potential marker of nitrosylated peptides.     

An investigation on the nature of the peptide at m/z 904, overexpressed in plasma of patients with colorectal cancer and familial adenomatous polyposis

In an investigation devoted to the search for plasma markers for colorectal cancer (CRC), carried out by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry, a series of overexpressed peptides were identified in the plasma of patients. Among them the peptide with molecular weight 903 Da was the most abundant one, with a mean +/- (SD) relative abundance of 37 +/- 17% and a frequency over 60%. Interestingly, also in plasma samples of ten subjects affected by familial adenomatous polyposis (FAP), the peptide with molecular weight 903 was overexpressed. In this investigation, MALDI/MS/MS experiments were carried out on the ion at m/z 904 detected in the MALDI mass spectra of CRC and FAP patients. The data analysis by SwissProt.2007.01.09 indicates that this peptide is due to the sequence RPPGFSPF, found in the kininogen-1 precursor, which is an alpha-2-thiol proteinase inhibitor. In the case of subjects affected by a particular FAP syndrome, the MALDI/MS/MS spectra were quite different from those obtained from CRC and FAP patients. In fact, two sequences have been evidenced: RPPGFSPF belonging to kininogen-1 precursor, and PRKSSSSR belonging to Forkhead box protein 01A.     

Identification of phosphorylated butyrylcholinesterase in human plasma using immunoaffinity purification and mass spectrometry

Paraoxon (diethyl 4-nitrophenyl phosphate) is an active metabolite of the common insecticide parathion and is acutely toxic due to the inhibition of cholinesterase (ChE) activity in the nervous systems. The inhibition of butyrylcholinesterase (BChE) activity by paraoxon is due to the formation of phosphorylated BChE adduct, and the detection of the phosphorylated BChE adduct in human plasma can serve as an exposure biomarker of organophosphate pesticides and nerve agents. In this study, we developed an immunoaffinity purification and liquid chromatography–mass spectrometry (LC–MS) strategy for identifying phosphorylated BChE in human plasma treated by paraoxon. BChE was captured by biotinylated anti-BChE polyclonal antibodies conjugated to streptavidin magnetic beads. Western blot analysis showed that the antibody was effective to recognize both native and modified BChE with high specificity. Using a purified BChE protein, we initially identified the exact phosphorylation site on the serine residue (S198) with a 108 Da modification by both MS/MS and accurately measured parent ion masses and quantified the extent of phosphorylation on S198 following paraoxon treatment to be >99.9%. Then, the phosphorylated BChE peptide in paraoxon-treated human plasma following immunoaffinity purification was successfully identified based on the accurate measured mass and retention time information initially obtained from the purified BChE protein. Thus, immunoaffinity purification combined with LC–MS represents a viable approach for the detection and quantification of phosphorylated BChE as an exposure biomarker of organophosphates and nerve agents.     

Post-translational modifications of recombinant B. cinerea EPG 6

The fungus Botrytis cinerea is a ubiquitous plant pathogen that infects more than 200 different plant species and causes substantial economic losses in a wide range of agricultural crops and harvested products. Endopolygalacturonases (EPGs) are among the first array of cell-wall-degrading enzymes secreted by fungi during infection. Up to 13 EPG glycoforms have been described for B. cinerea. The presence of multiple N-linked glycosylation modifications in BcPG1-6 is predicted by their deduced amino acid sequences. In this work, the glycosylation sites and the attached oligosaccharide structures on BcPG6 were analyzed. The molecular mass of the intact glycoprotein was determined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometric (MALDI-TOFMS) analysis. BcPG6 contains seven potential N-linked glycosylation sites. Occupancy of these glycosylation sites and the attached carbohydrate structures were analyzed by tryptic digestion followed by liquid chromatography/mass spectrometry (LC/MS) using a stepped orifice voltage approach. Five out of seven potential N-linked sites present in BcPG6 were determined to be occupied by high-mannose-type oligosaccharides. Four of them were readily determined to be at Asn58 (T3 peptide), Asn198 (T7 peptide), Asn237 (T9 peptide) and Asn256 (T11 peptide), respectively. Another was located on the T8 peptide, which contained two potential N-linked sites, Asn224 and Asn227 (SNNN224VTN227ITFK). LC/MS/MS of a sample treated with N-glycanase placed the glycan in this peptide at Asn224 rather than at Asn227. The potential glycosylation site on Asn146 (T6 peptide) was not glycosylated. In addition, two disulfide bonds were observed, linking the Cys residues within the T13 and T16 peptides.     

Characterization of the P13 membrane protein of Borrelia burgdorferi by mass spectrometry

Borrelia burgdorferi sensu lato is a tick-borne pathogen that causes Lyme disease. The characterization of membrane proteins from this and other pathogens may yield a better understanding of the mechanisms of infection and information useful for vaccine design. Characterization of the highly hydrophobic Borrelia outer membrane component P13 from a mutant (OspA- OspB- OspC- and OspD-) strain was undertaken by use of a combination of mass spectrometric methods. In a previous investigation, an electrospray ionization (ESI) mass spectrum of the intact protein provided an average molecular weight that was 20 Da lower than the predicted molecular weight. The mass deviation could be explained by a modification of the N-terminus of the protein such as pyroglutamylation (-17 Da) in combination with the experimental error of measurement, however more information was required. New structural information for this membrane protein was provided by peptide mapping with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF MS) and sequencing with ESI-quadrupole-TOF tandem MS.     

Electrospray low energy CID and MALDI PSD fragmentations of protonated sulfinamide cross-linked peptides

Murine S100A8 (A8) is a major cytoplasmic neutrophil protein and is converted to novel oxidation products containing Cys-epsilon amino-Lys sulfinamide cross-links and Met-sulfoxide by the neutrophil oxidant HOCl. Seven products were separated using RP-HPLC, with electrospray ionization mass spectrometry (ESI-MS) masses after deconvolution of 10,354, 10,388, +/- 1, and 20,707, +/- 3 Da, and all were resistant to reduction by dithiothreitol. The major products with masses of 10,354 Da contained Cys41-Lys34/35 intramolecular cross-links. Additional isomeric products with identical masses (10,354 Da) were isolated and peptide mapping and ESI/MS indicated that Cys41 forms covalent sulfinamide cross-links with either Lys6, Lys76, Lys83, or Lys87 present in A8. Electrospray low energy collisionally induced (CID) spectra of multiply-charged AspN digest peptides with sulfinamide cross-links contained characteristic fragmentations that corresponded to simple cleavage of the nitrogen-sulfur bond with charge retention on either of the fragment ions, allowing conformation of cross-linked peptides. Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) post source decay spectra of [M + H] + ions of the same sulfinamide-containing cross-linked peptides fragment similarly, but additional facile fragmentation reactions corresponding to formation of a protonated peptide containing de-hydroalanine were attributed to cleavage of the carbon-sulfur bond. In addition, lose of methanesulfenic acid from Met-sulfoxide was observed. A sulfinamide-containing adduct was isolated after incubation of the A8/HOCl reaction mixture with Lys or alpha N-acetyl Lys with masses of 10,500 or 10,542 Da. ESI/MS/MS and MALDI/post decay source (PSD) analysis of A8(32)-(57)-sulfinamide showed the same characteristic fragmentations as those in the sulfinamide cross-linked peptides, confirming the Cys41-Lys sulfinamide cross-link and suggesting that peptide-peptide sulfinamides may all fragment similarly, allowing ready identification of these cross-links in proteins from more complex biological materials.     

An integrated serum proteomic approach capable of monitoring the low molecular weight proteome with sequencing of intermediate to large peptides

The low‐abundance, low molecular weight serum proteome has high potential for the discovery of new biomarkers using mass spectrometry (MS). Because the serum proteome is large and complex, defining relative quantitative differences for a molecular species between comparison groups requires an approach with robust separation capability, high sensitivity, as well as high mass resolution. Capillary liquid chromatography (cLC)/MS provides both the necessary separation technique and the sensitivity to observe many low‐abundance peptides. Subsequent identification of potential serum peptide biomarkers observed in the cLC/MS step can in principle be accomplished by in series cLC/MS/MS without further sample preparation or additional instrumentation. In this report a novel cLC/MS/MS method for peptide sequencing is described that surpasses previously reported size limits for amino acid sequencing accomplished by collisional fragmentation using a tandem time‐of‐flight MS instrument. As a demonstration of the approach, two low‐abundance peptides with masses of ～4000–5000 Da were selected for MS/MS sequencing. The multi‐channel analyzer (MCA) was used in a novel way that allowed for summation of 120 fragmentation spectra for each of several customized collision energies, providing more thorough fragmentation coverage of each peptide with improved signal to noise. The peak list from this composite analysis was submitted to Mascot for identification. The two index peptides, 4279 Da and 5061 Da, were successfully identified. The peptides were a 39 amino acid immunoglobulin G heavy chain variable region fragment and a 47 amino acid fibrin alpha isoform C‐terminal fragment. The method described here provides the ability both to survey thousands of serum molecules and to couple that with markedly enhanced cLC/MS/MS peptide sequencing capabilities, providing a promising technique for serum biomarker discovery. Copyright © 2009 John Wiley & Sons, Ltd.     

Quantitative peptidomics of mouse pituitary: comparison of different stable isotopic tags

Determining the relative levels of neuropeptides in two samples is important for many biological studies. An efficient, sensitive and accurate technique for relative quantitative analysis involves tagging the peptides in the two samples with isotopically distinct labels, pooling the samples and analyzing them using liquid chromatography/mass spectrometry (LC/MS). In this study, we compared two different sets of isotopic tags for analysis of endogenous mouse pituitary peptides: succinic anhydride with either four hydrogens or deuteriums and [3-(2,5-dioxopyrrolidin-1-yloxycarbonyl)propyl]trimethylammonium chloride with either nine hydrogens or deuteriums. These two labels react with amines and impart either a negative charge (succinyl) or a positive charge (4-trimethylammoniumbutyryl (TMAB)). Every endogenous mouse pituitary peptide labeled with the light TMAB reagent eluted from the C18 reversed-phase column at essentially the same time as the corresponding peptide labeled with the heavy reagent. Most of the peptides labeled with succinyl groups also showed co-elution of the heavy- and light-labeled forms on LC/MS. The mass difference between the heavy and light TMAB reagents (9 Da per label) was larger than that of the heavy and light succinyl labels (4 Da per label), and for some peptides the larger mass difference provided more accurate determination of the relative abundance of each form. Altogether, using both labels, 82 peptides were detected in Cpe(fat/fat) mouse pituitary extracts. Of these, only 16 were detected with both labels, 41 were detected only with the TMAB label and 25 were detected only with the succinyl label. A number of these peptides were de novo sequenced using low-energy collisional tandem mass spectrometry. Whereas the succinyl group was stable to the collision-induced dissociation of the peptide, the TMAB-labeled peptides lost 59 Da per H9 TMAB group. Several peptides identified in this analysis represent previously undescribed post-translational processing products of known pituitary prohormones. In conclusion, both succinyl and TMAB isotopic labels are useful for quantitative peptidomics, and together these two labels provide more complete coverage of the endogenous peptides. Copyright (c) 2005 John Wiley & Sons, Ltd.     

The unanticipated loss of SO2 from sulfonamides in collision-induced dissociation

A potent and selective sulfonamide beta3 agonist with an excellent pharmacokinetic profile has recently been synthesized. During the analysis by liquid chromatography/tandem mass spectrometry (LC/MS/MS) of metabolites of the sulfonamide N-[4-[2-(2-hydroxy-2-pyridin-3-ylethylamino)ethyl]phenyl]-4-[4-(4-trifluoromethylphenyl)thiazol-2-yl]benzulfonamide (compound A), we observed loss of 64 Da for a few of the metabolites in the negative ion mode. Accurate mass measurements performed with Fourier transform ion cyclotron resonance (FTICR) mass spectrometry and quadrupole time-of-flight (Q-TOF) mass spectrometry suggested that the loss of 64 Da corresponded to the loss of SO(2). The same phenomenon was observed for a group of structurally related and commercially available compounds that also contain a sulfonamide moiety. MS/MS analysis of the fragment ions that had lost SO(2) in the ion source suggested that these ions were covalently bound rather than ion-molecule complexes. The neutral loss involving the cleavage of two bonds was unanticipated and suggested a complex rearrangement process. A mechanism for the loss of SO(2) has been proposed.     

Structural characterization of novel chemotactic and mastoparan peptides from the venom of the social wasp Agelaiapallipes pallipes by high-performance liquid chromatography/electrospray ionization tandem mass spectrometry

High-performance liquid chromatography/electrospray ionization mass spectrometry (HPLC/ESI-MS) and high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS) techniques were applied for the detection, purification, monitoring, and sequencing of two novel and biologically active peptides occurring at very low levels in the venom of the wasp Agelaia pallipes pallipes. These peptides were sequenced under LC/ESI-MS/MS conditions and designated as Agelaia-CP (I/L-L-G-T-I-L-G-L-L-K-G-I/L-NH2, MW 1207.8 Da) and Agelaia-MP (I/L-N-W-L-K-L-G-K-A-I-I-D-A-I/L-NH2, MW 1565.0 Da). The peptide Agelaia-CP showed no hemolytic activity, but it behaved as a mast cell degranulator and induced a potent chemotaxis in polymorphonucleated leukocyte (PMNL) cells, typical of a wasp chemotactic peptide. The peptide Agelaia-MP showed both powerful mast cell degranulation and hemolysis of washed rat red blood cells, and is thus assigned as a new member of the mastoparan family of peptides. Both peptides seem to be directly involved in the strong inflammatory reactions associated with wasp stings.     

Tandem mass spectrometry of multiply phosphorylated forms of a 'histidine-tag' derived from a recombinant protein kinase expressed in bacteria

When a histidine-tagged form of the protein kinase Aurora-2 was expressed in Escherichia coli, the purified product carried four to nine phosphate groups, although many fewer were expected. The amino-terminal tag had the sequence GSSHHHHHHSSGLVPRGSHMK-. Tryptic digestion of the product followed by analysis by liquid chromatography/mass spectrometry (LC/MS) and tandem mass spectrometry (MS/MS) showed that phosphorylation could occur on the five serine residues of the tag. Mono-, bis-, tris-, tetra- and pentaphosphorylated forms of the tag were detected, and their behavior in MS/MS was studied using a quadrupole/time-of-flight mass spectrometer. The MS/MS spectra were dominated by the products of neutral loss events (in 98 Da increments, each equivalent to loss of H3PO4), but sufficient b- and y-type sequence ions were detected to allow the locations of the phosphates to be specified in some cases. The assignment of phosphorylation sites for incompletely phosphorylated forms of the tag peptide was challenging, but it appeared that Ser-10 and Ser-11 of the tag were more likely to be phosphorylated than Ser-2 and Ser-3.     

Characterization of glycosylation sites for a recombinant IgG1 monoclonal antibody and a CTLA4-Ig fusion protein by liquid chromatography-mass spectrometry peptide mapping

Liquid chromatography mass spectrometry (LC-MS) peptide mapping can be a versatile technique for characterizing protein glycosylation sites without the need to remove the attached glycans as in conventional oligosaccharide mapping methods. In this way, both N-linked and O-linked sites of glycosylation can each be directly identified, characterized, and quantified by LC-MS as intact glycopeptides in a single experiment. LC-MS peptide mapping of the individual glycosylation sites avoids many of the limitations of preparing and analyzing an entire pool of released N-linked oligosaccharides from all sites mixed together. In this study, LC interfaced to a linear ion trap mass spectrometer (ESI-LIT-MS) were used to characterize the glycosylation of a recombinant IgG1 monoclonal antibody and a CTLA4-Ig fusion protein with multiple sites of N-and O-glycosylation. Samples were reduced, S-carboxyamidomethylated, and cleaved with either trypsin or endoproteinase Asp-N. Enhanced detection for minor IgG1 glycoforms (～0.1 to 1.0 mol% level) was obtained by LC-MS of the longer 32-residue Asp-N glycopeptide (4+ protonated ion) compared to the 9-residue tryptic glycopeptide (2+ ion). LC-MS peptide mapping was run according to a general procedure: (1) Locate N-linked and/or O-linked sites of glycosylation by selected-ion-monitoring of carbohydrate oxonium fragment ions generated by ESI in-source collision-induced dissociation (CID), i.e. 204, 366, and 292 Da marker ions for HexNAc, HexNAc-Hex, and NeuAc, respectively; (2) Characterize oligosaccharides at each site via MS and MSMS. Use selected ion currents (SIC) to estimate relative amounts of each glycoform; and (3) Measure the percentage of site-occupancy by searching for any corresponding nonglycosylated peptide.     

Analysis of high mass peptides using a novel matrix-assisted laser desorption/ionisation quadrupole ion trap time-of-flight mass spectrometer

A novel matrix-assisted laser desorption/ionisation quadrupole ion trap time-of-flight (MALDI QIT ToF) mass spectrometer has been used to analyse high mass peptide ions exceeding 2000 Da. Human adrenocorticotropic hormone (fragment 18-39) and oxidised bovine insulin chain B were utilised to evaluate the performance of the instrument both in MS and in MS/MS mode. Its ability to efficiently isolate ions and to fragment them using collisionally activated decomposition (CAD) has been demonstrated using mixtures diluted to the low-femtomole level on target. Additionally, multiple stage mass spectrometry (MS/MS/MS) provides a second-generation product ion spectrum in which new fragment ions are detected and new stretches of amino acids are identified.     

Fast analysis of low molecular mass compounds present in snake venom: identification of ten new pyroglutamate-containing peptides

Characterization of the peptide content in snake venoms can be an important tool for the investigation of new pharmacological lead compounds. For this purpose, single-step analysis of crude venoms has recently been demonstrated using mass spectrometry (MS) techniques. Reproducible profiles of ions in MS and MS/MS spectra may also be used to compare venoms from different species. In this work matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) was used to obtain mass patterns of the major peptides (<8 kDa) found in pooled venoms from the genera Bothrops and Crotalus. Venoms from five different Bothrops species (B. jararaca, B. insularis, B. alternatus, B. jararacussu, and B. neuwiedi) and three Crotalus species (C. viridis, C. adamanteus and C. durissus terrificus) were analyzed. In agreement with other reports, venoms from Bothrops species contained a variety of peptides in the range m/z 1000-1500, and in some samples larger components (m/z 7000-8000) were detected. In the Crotalus species venoms were rich in peptides ranging from m/z 1000-1500 and 4000-5500. MS/MS experiments on the low molecular mass peptides (m/z 1000-1500) confirmed the presence of ten new bradykinin-potentiating peptides among venoms from genera Bothrops and Crotalus. In order to determine whether additional peptides could be identified after partial purification, B. jararaca venom was subjected to size-exclusion chromatography on Sephacryl S-200, and two distinct low molecular mass pools were analyzed further by MALDI-TOFMS. No additional peptides were detected from the pool with masses below 2000 Da but a substantial improvement with better resolution was observed for the pool with masses above 7000 Da, indicating that complex samples such as crude snake venoms can be analyzed for low molecular mass peptides using a single-step procedure.     

人肝癌细胞系HLE细胞表面抗原多肽的纳升电喷雾串联质谱从头测序分析

肿瘤细胞表面的抗原多肽能够被细胞毒T淋巴细胞特异性识别而引起免疫应答,因此有可能用于研制基于多肽的抗肿瘤疫苗。用弱酸将人肝癌细胞系HLE细胞表面抗原多肽和人正常肝细胞表面多肽洗脱后,经RP-HPLC分离,选择HLE细胞表面特异性多肽进行纳升电喷雾串联质谱(nanoESI-MS/MS)测序,共测定5个色谱峰中的20个多肽序列,分子量分布范围为1000~2000 Da。借助M asSeq软件分析出其中12个多肽的序列。经数据库查寻,其中的3个肽段分别来自钙调节蛋白、核蛋白S19和伴侣蛋白10。这些多肽的生物学功能及与肿瘤的关系值得深入研究。该研究表明nanoESI-MS/MS是测定微量混合多肽序列的最有效方法。     

Characterization of fifty-one flavonoids in a Chinese herbal prescription Longdan Xiegan Decoction by high-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry and photodiode array detection

High-performance liquid chromatography coupled to electrospray ionization (ESI) tandem mass spectrometry and photodiode array detection (HPLC-DAD-ESI-MS(n)) was developed to identify and characterize the flavonoids in a Chinese formulated preparation, Longdan Xiegan Decoction (LXD). In total, fifty-one flavonoids (27 flavones, 10 flavanones, 7 chalcones, 5 flavonols and 2 isoflavones) were characterized. Eighteen compounds among them including a newly detected flavonoid, naringin, from the ingredient herbs, were unambiguously determined by comparing the retention times (t(R)), UV spectral data and mass fragmentation behaviors with those of the reference compounds. Another thirty-three compounds were tentatively identified by referencing to the reported data of their UV and MS spectra. The ESI-MS/MS fragmentation behavior of flavones (OMe-substituted, O-glycosides, C-glycosides), chalcones, flavonols and their appropriate characteristic pathways were proposed. In negative ion ESI-MS all the flavonoids yielded prominent [M--H](-) ions in the first order mass spectra. Fragmentation with a loss of mass of 15 Da (CH(3)), 18 Da (H(2)O), 28 Da (CO), 44 Da (CO(2)), 56 Da (2CO) and the residues of glucose and glucuronic acid observed in the MS/MS spectra were useful for aiding the structural identification of the flavonoids investigated.