Sulfite-mediated oxidation of myeloperoxidase to a free radical: immuno-spin trapping detection in human neutrophils

Previous studies focused on catalyzed oxidation of (bi)sulfite, leading to the formation of the reactive sulfur trioxide ((•)SO3(-)), peroxymonosulfate ((-)O3SOO(•)), and sulfate (SO4(•-)) anion radicals, which can damage target proteins and oxidize them to protein radicals. It is known that these very reactive sulfur- and oxygen-centered radicals can be formed by oxidation of (bi)sulfite by peroxidases. Myeloperoxidase (MPO), an abundant heme protein secreted from activated neutrophils that play a central role in host defense mechanisms, allergic reactions, and asthma, is a likely candidate for initiating the respiratory damage caused by sulfur dioxide. The objective of this study was to examine the oxidative damage caused by (bi)sulfite-derived free radicals in human neutrophils through formation of protein radicals. We used immuno-spin trapping and confocal microscopy to study the protein oxidations driven by sulfite-derived radicals. We found that the presence of sulfite can cause MPO-catalyzed oxidation of MPO to a protein radical in phorbol 12-myristate 13-acetate-activated human neutrophils. We trapped the MPO-derived radicals in situ using the nitrone spin trap 5,5-dimethyl-1-pyrroline N-oxide and detected them immunologically as nitrone adducts in cells. Our present study demonstrates that myeloperoxidase initiates (bi)sulfite oxidation leading to MPO radical damage, possibly leading to (bi)sulfite-exacerbated allergic reactions.

Simplified synthesis of isotopically labeled 5,5-dimethyl-pyrroline N-oxide

5,5-Dimethylpyrroline N-oxide (¹⁵N) and 5,5-di(trideuteromethyl)pyrroline N-oxide were synthesized from the respective isotopically labeled 2-nitropropane analogs obtained from the reaction of sodium nitrate with 2-halopropanes. This facile, straightforward process allows synthesizing isotopically labeled DMPO analogs in a 4-step reaction without special equipment.

Mass spectrometric determination of IgG subclass-specific glycosylation profiles in siblings discordant for myositis syndromes

Many autoimmune conditions are believed to result from chronic inflammation as a consequence of the interaction of genetic and environmental factors in susceptible individuals. One common feature in some autoimmune diseases is the decrease in terminal galactosylation of the constant region N-glycan of the total plasma immunoglobulin. To determine whether a similar pattern is characteristic for the autoimmune disorder myositis, we analyzed the antibody subclass specific glycosylation in patients with myositis, their asymptomatic siblings, and healthy unrelated age- and sex-matched controls. The antibody subclass specific glycosylation was determined from the LC-MS analyses of the IgG glycopeptides generated by trypsin digestion of the antibody heavy chain. The glycosylation profiles of the IgG subclasses were determined relative to the total abundance of all glycoforms. We found elevated amounts of glycoforms lacking terminal galactose in myositis patients. Pairwise statistical analyses reveals that galactosylation is statistically different between the myositis patients and control groups. Furthermore, the trend analysis for glycosylation indicates a pattern of decreasing galactosylation in the order controls ≥ siblings ≥ myositis patients, suggesting the existence of a genetic, immune-related predisposition in the group of asymptomatic siblings that can be detected before the onset of clinical symptoms at the level of plasma proteins.

Site-specific radical formation in DNA induced by Cu(II)-H₂O₂ oxidizing system, using ESR, immuno-spin trapping, LC-MS, and MS/MS

Oxidative stress-related damage to the DNA macromolecule produces a multitude of lesions that are implicated in mutagenesis, carcinogenesis, reproductive cell death, and aging. Many of these lesions have been studied and characterized by various techniques. Of the techniques that are available, the comet assay, HPLC-EC, GC-MS, HPLC-MS, and especially HPLC-MS/MS remain the most widely used and have provided invaluable information on these lesions. However, accurate measurement of DNA damage has been a matter of debate. In particular, there have been reports of artifactual oxidation leading to erroneously high damage estimates. Further, most of these techniques measure the end product of a sequence of events and thus provide only limited information on the initial radical mechanism. We report here a qualitative measurement of DNA damage induced by a Cu(II)-H₂O₂ oxidizing system using immuno-spin trapping (IST) with electron paramagnetic resonance (EPR), MS, and MS/MS. The radical generated is trapped by DMPO immediately upon formation. The DMPO adduct formed is initially EPR active but subsequently is oxidized to the stable nitrone, which can then be detected by IST and further characterized by MS and MS/MS.

CD34 Antigen: Determination of Specific Sites of Phosphorylation In Vitro and In Vivo

CD34, a type I transmembrane glycoprotein, is a surface antigen which is expressed on several cell types, including hematopoietic progenitors, endothelial cells, as well as mast cells. Recently, CD34 has been described as a marker for epidermal stem cells in mouse hair follicles, and is expressed in outer root sheath cells of the human hair follicle. Although the biological function and regulation of CD34 is not well understood, it is thought to be involved in cell adhesion as well as possibly having a role in signal transduction. In addition, CD34 was shown to be critical for skin tumor development in mice, although the exact mechanism remains unknown.Many proteins' functions and biological activities are regulated through post-translational modifications. The extracellular domain of CD34 is heavily glycosylated but the role of these glycans in CD34 function is unknown. Additionally, two sites of tyrosine phosphorylation have been reported on human CD34 and it is known that CD34 is phosphorylated, at least in part, by protein kinase C; however, the precise location of the sites of phosphorylation has not been reported. In an effort to identify specific phosphorylation sites in CD34 and delineate the possible role of protein kinase C, we undertook the identification of the in vitro sites of phosphorylation on the intracellular domain of mouse CD34 (aa 309-382) following PKC treatment. For this work, we are using a combination of enzymatic proteolysis and peptide sequencing by mass spectrometry. After which the in vivo sites of phosphorylation of full-length mouse CD34 expressed from HEK293F cells were determined. The observed in vivo sites of phosphorylation, however, are not consensus PKC sites, but our data indicate that one of these sites may possibly be phosphorylated by AKT2. These results suggest that other kinases, as well as PKC, may have important signaling functions in CD34.

Biotinylated analogue of the spin-trap 5,5-dimethyl-1-pyrroline-N-oxide for the detection of low-abundance protein radicals by mass spectrometry

Protein radicals are implicated in oxidative stress and are associated with a wide range of diseases and disorders. In the present work, we describe the specific application of a newly synthesized nitrone spin trap, Bio-SS-DMPO, for the detection of these highly reactive species by mass spectrometry (MS). Bio-SS-DMPO is a biotinylated analogue of the spin-trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) that allows for specific capture of the protein(s)/peptide(s) labeled by the spin-trap on a (strept)avidin-bound solid matrix. The disulfide bond in the linker arm joining biotin to DMPO can be cleaved to release captured spin-adduct peptide from the solid matrix. This (strept)avidin-based affinity purification reduces the complexity of the samples prior to MS analyses, thereby facilitating the location of the sites of spin trap addition. In addition, the biotin moiety on the spin-trap can efficiently be probed with (strept)avidin-conjugated reporter. This offers an effective means to visualize the presence of DMPO-adducted proteins in intact cells.

Comparison of metal and metal oxide media for phosphopeptide enrichment prior to mass spectrometric analyses

Several affinity resins consisting of ionic metals or metal oxides were investigated for their phosphopeptide enrichment capabilities with subsequent mass spectrometric analyses. Commercially-available enrichment metal oxide affinity chromatography (MOAC) resins using manufacturer's and/or published protocols were compared and evaluated for the most efficient and selective method that could be implemented as a standard enrichment procedure. From these comparative analyses, using a tryptic digest of casein proteins, it was determined that in our hands, two of the resins out-performed the others based on a variety of criteria, including the number of phosphorylation sites identified during MS analyses, the lower numbers of nonspecifically bound peptides observed, and the limits of detection. Applicability of these enrichment resins to a complex biological mixture was investigated. For this work, a mixture of avian histones was digested, subjected to titanium dioxide phosphopeptide enrichment, and analyzed by mass spectrometry. Eight phosphorylated tryptic peptides were observed following enrichment and subsequent LC/MS/MS analyses. Of note, seven of the eight phosphopeptides were not observed without titanium dioxide enrichment. From these analyses, four sites of phosphorylation were unequivocally determined, two of which have not been reported previously. Four additional phosphopeptides were observed; however, the site of phosphorylation could not be distinguished but was localized to one of two possible amino acids. These methods should aid in the investigation of proteins post-translationally modified with phosphate, especially those present at low concentrations as was demonstrated by successful enrichment at the femtomole level.

Mass spectrometric identification of oxidative modifications of tryptophan residues in proteins: chemical artifact or post-translational modification?

Oxidative modification of tryptophan to kynurenine (KYN) and N-formyl kynurenine (NFK) has been described in mitochondrial proteins associated with redox metabolism, and in human cataract lenses. To a large extent, however, previously reported identifications of these modifications were performed using peptide mass fingerprinting and/or tandem-MS data of proteins separated by gel electrophoresis. To date, it is uncertain whether NFK and KYN may represent sample handling artifacts or exclusively post-translational events. To address the problem of the origin of tryptophan oxidation, we characterized several antibodies by liquid chromatography-tandem mass spectrometry, with and without the use of electrophoretic separation of heavy and light chains. Antibodies are not normally expected to undergo oxidative modifications, however, several tryptophan (Trp) residues on both heavy and light chains were found extensively modified to both doubly oxidized Trp and KYN following SDS-PAGE separation and in-gel digestion. In contrast, those residues were observed as non-modified upon in-solution digestion. These results indicate that Trp oxidation may occur as an artifact in proteins separated by SDS-PAGE, and their presence should be carefully interpreted, especially when gel electrophoretic separation methods are employed.

Structural characterization of the conformational change in calbindin-D28k upon calcium binding using differential surface modification analyzed by mass spectrometry

Calbindin-D28k is a calcium binding protein with six EF hand domains. Calbindin-D28k is unique in that it functions as both a calcium buffer and a sensor protein. It is found in many tissues, including brain, pancreas, kidney, and intestine, playing important roles in each. Calbindin-D28k is known to bind four calcium ions and upon calcium binding undergoes a conformational change. The structure of apo calbindin-D28k is in an ordered state, transitioning into a disordered state as calcium is bound. Once fully loaded with four calcium ions, it again takes on an ordered state. The solution structure of disulfide-reduced holo-calbindin-D28k has been determined by NMR, while the structure of apo calbindin-D28k has yet to be determined. Differential surface modification of lysine and histidine residues analyzed by mass spectrometry has been used in this study to identify, for the first time, the specific regions of calbindin-D28k undergoing conformational changes between the holo and apo states. Using differential surface modification in combination with mass spectrometry, EF hands 1 and 4 as well as the linkers before EF hand 1 and the linkers between EF hands 4 and 5 and EF hands 5 and 6 were identified as regions of conformational change between apo and holo calbindin-D28k. Under the experimental conditions employed, EF hands 2 and 6, which are known not to bind calcium, were unaffected in either form. EF hand 2 is highly accessible; however, EF hand 6 was determined not to be surface accessible in either form. Previous research has identified a disulfide bond between cysteines 94 and 100 in the holo state. Until now, it was unknown whether this bond also exists in the apo form. Our data confirm the presence of the disulfide bond between cysteines 94 and 100 in the holo form and indicate that there is predominantly no disulfide bond between these residues in the apoprotein.

Spin scavenging analysis of myoglobin protein-centered radicals using stable nitroxide radicals: characterization of oxoammonium cation-induced modifications

Spin scavenging combined with chromatographic and mass spectrometric procedures can, in principle, be employed to detect and identify protein-based radicals within complex biological matrices. This approach is based on the well-known ability of stable synthetic nitroxide radicals to scavenge carbon-centered radicals, forming stable diamagnetic addition products. Hence, characterization of these addition products would allow for the identification of specific free radicals. In the present work, we have explored the use of the stable nitroxide radical 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPOL) in scavenging protein-based radicals generated in a horse heart metmyoglobin/hydrogen peroxide (metMb/H(2)O(2)) system. Inclusion of a substoichiometric amount of TEMPOL in the metMb/H(2)O(2) system resulted in a complete loss of peroxyl and tyrosyl radical signals and effectively inhibited the formation of oxidatively damaged heme species, as monitored by electron paramagnetic resonance and reversed-phase liquid chromatography. Scavenging of globin radicals by TEMPOL did not lead to the formation of stable diamagnetic addition adducts; in fact, reversed-phase liquid chromatographic studies and oxygen electrode measurements indicated that TEMPOL acts as a catalyst and is recycled in this system. The oxoammonium cation generated in the course of this reaction initiated secondary reactions resulting in the formation of a free carbonyl on the N-terminal Gly-residue of the protein. This oxidative deamination was confirmed through the combined use of reversed-phase liquid chromatographic purification, tandem MS experiments, and chemical analysis (e.g., by use of 2,4-dinitrophenyl hydrazine). The results reveal the pitfalls inherent in using stable nitroxide radicals such as TEMPOL to identify sites of radical formation on hemoproteins.

Site-specific carboxypeptidase B1 tyrosine nitration and pathophysiological implications following its physical association with nitric oxide synthase-3 in experimental sepsis

LPS-induced sepsis results in oxidative modification and inactivation of carboxypeptidase B1 (CPB1). In this study, immunoprecipitated CPB1 was probed for tyrosine nitration using monoclonal nitrotyrosine-specific Abs in a murine model of LPS-induced sepsis. Tyrosine nitration of CPB1 was significantly reduced in the presence of NO synthase (NOS) inhibitors and the xanthine oxidase (XO) inhibitor allopurinol and in NOS-3 knockout (KO) mice. CPB1 tyrosine nitration and loss of activity by the concerted action of NOS-3 and XO were also confirmed in vitro using both the NO donor 3-morpholinosydnonimine and peroxynitrite. Liquid chromatography/tandem mass spectrometry data indicated five sites of tyrosine nitration in vitro including Tyr(248), the tyrosine at the catalytic site. The site- and protein-specific nitration of CPB1 and the possible high nitration yield to inactivate it were elucidated by confocal microscopy. The studies indicated that CPB1 colocalized with NOS-3 in the cytosol of sinus-lining cells in the red pulp of the spleen. Further analysis of CPB1-immunoprecipitated samples indicated immunoreactivity to a monoclonal NOS-3 Ab, suggesting protein complex formation with CPB1. XO and NOS inhibitors and NOS-3 KO mice injected with LPS had decreased levels of C5a in spleens of septic mice, indicating peroxynitrite as a possible cause for CPB1 functional alteration. Thus, CPB1 colocalization, coupling, and proximity to NOS-3 in the sinus-lining cells of spleen red pulp could explain the site-specific tyrosine nitration and inactivation of CPB1. These results open up new avenues for the investigation of several enzymes involved in inflammation and their site-specific oxidative modifications by protein-protein interactions as well as their role in sepsis.

Elucidation of O-glycosylation structures of the beta-amyloid precursor protein by liquid chromatography-mass spectrometry using electron transfer dissociation and collision induced dissociation

Accumulation and deposition of beta-amyloid peptide, a major constituent in neuritic plaques are hallmarks of Alzheimer's disease (AD) and AD-related neurodegenerative diseases. beta-Amyloid (Abeta) is derived from the proteolytic cleavage of amyloid precursor protein (APP), a transmembrane protein present in three major isoforms in brain comprising 695, 751 and 770 amino acids, respectively. Among other post-translational modifications, APP is modified during maturation by N- and O-glycosylation, which are thought to be responsible for its expression and secretion. Unlike N-glycosylation, no sites of O-glycosylation of APP have previously been reported. We report here the identification of three specific O-glycosylation sites of the secreted APP695 (sAPP695) produced in CHO cells, using a combination of high-performance liquid chromatography and electrospray-tandem mass spectrometry. With the use of electron transfer dissociation and collision induced dissociation (ETD and CID), we identified type, composition and structures of the Core 1 type O-linked glycans attached at the residues Thr 291, Thr 292 and Thr 576 of the full-length APP695. The glycosylations comprise multiple short glycans, containing N-acetyl galactosamine (GalNAc), Gal-GalNAc and sialic acid terminated structures. The presence of the glycopeptides in the tryptic mixture was identified using the CID-generated sugar oxonium ions. ETD proved to be valuable for the unambiguous identification of the modified sites as ETD fragmentation occurred along the peptide backbone with little or no cleavage of the glycans. Thus, the combination of the CID and ETD techniques in LC-MS is shown here, as a powerful tool for de novo identification of O-glycosylations at unknown modification sites in proteins.

Immuno-spin trapping of protein and DNA radicals: "tagging" free radicals to locate and understand the redox process

Biomolecule-centered radicals are intermediate species produced during both reversible (redox modulation) and irreversible (oxidative stress) oxidative modification of biomolecules. These oxidative processes must be studied in situ and in real time to understand the molecular mechanism of cell adaptation or death in response to changes in the extracellular environment. In this regard, we have developed and validated immuno-spin trapping to tag the redox process, tracing the oxidatively generated modification of biomolecules, in situ and in real time, by detecting protein- and DNA-centered radicals. The purpose of this methods article is to introduce and update the basic methods and applications of immuno-spin trapping for the study of redox biochemistry in oxidative stress and redox regulation. We describe in detail the production, detection, and location of protein and DNA radicals in biochemical systems, cells, and tissues, and in the whole animal as well, by using immuno-spin trapping with the nitrone spin trap 5,5-dimethyl-1-pyrroline N-oxide.

Glycosylation profiles of epitope-specific anti-beta-amyloid antibodies revealed by liquid chromatography-mass spectrometry

Alzheimer's disease (AD) is the most prevalent form of age-related neurodementia. The accumulation of beta-amyloid polypeptide (Abeta) in brain is generally believed to be a key event in AD. The recent discovery of physiological beta-amyloid autoantibodies represents a promising perspective for treatment and early diagnosis of AD. The mechanisms by which natural beta-amyloid autoantibodies prevent neurodegeneration are currently unknown. The aim of the present study was to analyze the N-linked glycosylation of a plaque-specific, monoclonal antibody (clone 6E10) relevant for immunotherapy of AD, in comparison with the glycosylation pattern of an Abeta autoantibody isolated from an IgG source. Liquid chromatography in combination with tandem mass spectrometry was used to analyze the glycopeptides generated by enzymatic degradation of the antibodies reduced and alkylated heavy chains. The oligosaccharide pattern of the 6E10 antibody shows primarily core-fucosylated biantennary complex structures and, to a low extent, tri- and tetragalactosyl glycoforms, with or without terminal sialic acids. The glycans associated with the serum anti-Abeta autoantibodies are of the complex, biantennary-type, fucosylated at the first N-acetyl glucosamine residue of the trimannosyl chitobiose core and contain zero to two galactose residues, and zero to one terminal sialic acid, with or without bisecting N-acetyl glucosamine. Glycosylation analysis of the Abeta-autoantibody performed at the peptide level revealed all four human IgG subclasses, with IgG(1) and IgG(2) as the dominant subclasses.

Immuno-spin trapping of a post-translational carboxypeptidase B1 radical formed by a dual role of xanthine oxidase and endothelial nitric oxide synthase in acute septic mice

Post-translational modification of proteins due to exposure to radicals and other reactive species are markers of metabolic and inflammatory oxidative stress such as sepsis. This study uses the nitrone spin-trap DMPO and a combination of immuno-spin trapping and mass spectrometry to identify in vivo products of radical reactions in mice. We report the detection of dose-dependent production of DMPO-carboxypeptidase B1 (CPB1) adducts in the spleens of mice treated with lipopolysaccharide (LPS). Additionally, we report significant detection of DMPO-CPB1 adducts in mice experiencing normal physiological conditions. Treatments with inhibitors and experiments with knock-out mice indicate that xanthine oxidase and endothelial nitric oxide synthase are important sources of the reactive species that lead to CPB1 adduct formation. We also report a significant loss of CPB1 activity following LPS challenge in conjunction with an increase in CPB1 protein accumulation. This suggests the presence of a possible mechanism for CPB1 activity loss with compensatory protein production.

Cu,Zn-superoxide dismutase-driven free radical modifications: copper- and carbonate radical anion-initiated protein radical chemistry

The understanding of the mechanism, oxidant(s) involved and how and what protein radicals are produced during the reaction of wild-type SOD1 (Cu,Zn-superoxide dismutase) with H2O2 and their fate is incomplete, but a better understanding of the role of this reaction is needed. We have used immuno-spin trapping and MS analysis to study the protein oxidations driven by human (h) and bovine (b) SOD1 when reacting with H2O2 using HSA (human serum albumin) and mBH (mouse brain homogenate) as target models. In order to gain mechanistic information about this reaction, we considered both copper- and CO3(*-) (carbonate radical anion)-initiated protein oxidation. We chose experimental conditions that clearly separated SOD1-driven oxidation via CO(*-) from that initiated by copper released from the SOD1 active site. In the absence of (bi)carbonate, site-specific radical-mediated fragmentation is produced by SOD1 active-site copper. In the presence of (bi)carbonate and DTPA (diethylenetriaminepenta-acetic acid) (to suppress copper chemistry), CO(*-) produced distinct radical sites in both SOD1 and HSA, which caused protein aggregation without causing protein fragmentation. The CO(*-) produced by the reaction of hSOD1 with H2O2 also produced distinctive DMPO (5,5-dimethylpyrroline-N-oxide) nitrone adduct-positive protein bands in the mBH. Finally, we propose a biochemical mechanism to explain CO(*-) production from CO2, enhanced protein radical formation and protection by (bi)carbonate against H2O2-induced fragmentation of the SOD1 active site. Our present study is important for establishing experimental conditions for studying the molecular mechanism and targets of oxidation during the reverse reaction of SOD1 with H2O2; these results are the first step in analysing the critical targets of SOD1-driven oxidation during pathological processes such as neuroinflammation.

Identification of protein radicals formed in the human neuroglobin-H2O2 reaction using immuno-spin trapping and mass spectrometry

Neuroglobin (Ngb) is a recently discovered protein that shows only minor sequence similarity with myoglobin and hemoglobin but conforms to the typical 3-over-3 alpha-helical fold characteristic of vertebrate globins. An intriguing feature of Ngb is its heme hexacoordination in the absence of external ligands, observed both in the ferrous and in the ferric (met) forms. In Ngb, the imidazole of a histidine residue (His-64) in the distal position, above the heme plane, provides the sixth coordination bond. In this work, a valine residue was introduced at position 64 (H64V variant) to clarify the possible role(s) of the distal residue in protecting the heme iron of Ngb from attack by strong oxidants. SDS-PAGE analyses revealed that the oxidation of the H64V variant of metNgb by H 2O 2 resulted in the formation of dimeric and trimeric products in contrast to the native protein. Dityrosine cross-links were shown by their fluorescence to be present in the oligomeric products. When the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was included in the reaction mixture, nitrone adducts were detected by immuno-spin trapping. The specific location of the DMPO adducts on the H64V variant protein was determined by a mass spectrometry method that combines off-line immuno-spin trapping and chromatographic procedures. This method revealed Tyr-88 to be the site of modification by DMPO. The presence of His-64 in the wild-type protein results in the nearly complete loss of detectable radical adducts. Together, the data support the argument that wild-type Ngb is protected from attack by H 2O 2 by the coordinated distal His.

Procainamide, but not N-acetylprocainamide, induces protein free radical formation on myeloperoxidase: a potential mechanism of agranulocytosis

Procainamide (PA) is a drug that is used to treat tachycardia in postoperative patients or for long-term maintenance of cardiac arrythmias. Unfortunately, its use has also been associated with agranulocytosis. Here, we have investigated the metabolism of PA by myeloperoxidase (MPO) and the formation of an MPO protein free radical. We hypothesized that PA oxidation by MPO/H 2O 2 would produce a PA cation radical that, in the absence of a biochemical reductant, would lead to the free radical oxidation of MPO. We utilized a novel anti-DMPO antibody to detect DMPO (5,5-dimethyl-1-pyrroline N-oxide) covalently bound to protein, which forms by the reaction of DMPO with a protein free radical. We found that PA metabolism by MPO/H 2O 2 induced the formation of DMPO-MPO, which was inhibited by MPO inhibitors and ascorbate. N-acetyl-PA did not cause DMPO-MPO formation, indicating that the unsubstituted aromatic amine was more oxidizable. PA had a lower calculated ionization potential than N-acetyl-PA. The DMPO adducts of MPO metabolism, as analyzed by electron spin resonance spectroscopy, included a nitrogen-centered radical and a phenyl radical derived from PA, either of which may be involved in the free radical formation on MPO. Furthermore, we also found protein-DMPO adducts in MPO-containing, intact human promyelocytic leukemia cells (HL-60). MPO was affinity-purified from HL-60 cells treated with PA/H 2O 2 and was found to contain DMPO using the anti-DMPO antibody. Mass spectrometry analysis confirmed the identity of the protein as human MPO. These findings were also supported by the detection of protein free radicals with electron spin resonance in the cellular cytosolic lysate. The formation of an MPO protein free radical is believed to be mediated by free radical metabolites of PA, which we characterized by spin trapping. We propose that drug-induced free radical formation on MPO may play a role in the origin of agranulocytosis.

Global changes in and characterization of specific sites of phosphorylation in mouse and human histone H1 Isoforms upon CDK inhibitor treatment using mass spectrometry

Global changes in the phosphorylation state of human H1 isoforms isolated from UL3 cells have been investigated using mass spectrometry. Relative changes in H1 phosphorylation between untreated cells and cells treated with dexamethasone or various CDK inhibitors were determined. The specific cyclin-dependent kinase consensus sites of phosphorylation on the histone H1 isoforms that show changes in phosphorylation were also investigated. Three sites of phosphorylation on histone H1.4 isoforms have been identified.

Identifying the site of spin trapping in proteins by a combination of liquid chromatography, ELISA, and off-line tandem mass spectrometry

An off-line mass spectrometry method that combines immuno-spin trapping and chromatographic procedures has been developed for selective detection of the nitrone spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) covalently attached to proteins, an attachment which occurs only subsequent to DMPO trapping of free radicals. In this technique, the protein-DMPO nitrone adducts are digested to peptides with proteolytic agents, peptides from the enzymatic digest are separated by HPLC, and enzyme-linked immunosorbent assays (ELISA) using polyclonal anti-DMPO nitrone antiserum are used to detect the eluted HPLC fractions that contain DMPO nitrone adducts. The fractions showing positive ELISA signals are then concentrated and characterized by tandem mass spectrometry (MS/MS). This method, which constitutes the first liquid chromatography-ELISA-mass spectrometry (LC-ELISA-MS)-based strategy for selective identification of DMPO-trapped protein residues in complex peptide mixtures, facilitates location and preparative fractionation of DMPO nitrone adducts for further structural characterization. The strategy is demonstrated for human hemoglobin, horse heart myoglobin, and sperm whale myoglobin, three globin proteins known to form DMPO-trappable protein radicals on treatment with H(2)O(2). The results demonstrate the power of the new experimental strategy to select DMPO-labeled peptides and identify sites of DMPO covalent attachments.

Phosphorylation site analysis of the anti-inflammatory and mRNA-destabilizing protein tristetraprolin

Tristetraprolin (TTP) is a member of the CCCH zinc finger proteins and is an anti-inflammatory protein. Mice deficient in TTP develop a profound inflammatory syndrome with erosive arthritis, autoimmunity and myeloid hyperplasia. TTP binds to mRNA AU-rich elements with high affinity for UUAUUUAUU nucleotides and causes destabilization of those mRNA molecules. TTP is phosphorylated extensively in vivo and is a substrate for multiple protein kinases in vitro. A number of approaches have been used to identify its phosphorylation sites. This article highlights the recent progress and different approaches utilized for the identification of phosphorylation sites in mammalian TTP. Important but limited results are obtained using traditional methods, including in vivo labeling, site-directed mutagenesis, phosphopeptide mapping and protein sequencing. Mass spectrometry (MS), including MALDI/MS, MALDI/MS/MS, liquid chromatography/MS/MS, immobilized metal ion affinity chromatography (IMAC)/MALDI/MS/MS and multidimensional protein identification technology has led the way in identifying TTP phosphorylation sites. The combination of these approaches has identified multiple phosphorylation sites in mammalian TTP, some of which are predicted by motif scanning to be phosphorylated by several protein kinases. This information should provide the molecular basis for future investigation of TTP's regulatory functions in controlling proinflammatory cytokines.

Diversity in penaeidin antimicrobial peptide form and function

Penaeidins are a diverse family of two-domain antimicrobial peptides expressed in shrimp. Variation in penaeidin sequence results in functional diversity, which was discovered using synthetic reproductions of native penaeidins. An isoform of penaeidin class 3 from Litopenaeus setiferus (Litset Pen3-4) was synthesized using native ligation and compared directly with the synthetic penaeidin class 4 known to be expressed in the same organism. New antimicrobial activity data are included in this review that emphasize differences in effectiveness that are apparent from a direct comparison of two classes. A novel approach to intact penaeidin analysis is presented in the form of Fourier Transform Ion-Cyclotron Resonance Mass Spectrometry, which has implications for the identification of individual penaeidin isoforms without chemical modification or enzymatic cleavage. The new information included in this review helps gather the perspective on relevance of penaeidin diversity to antimicrobial function, the use of synthetic peptides as tools to evaluate specific immune functions and the application of high mass resolution, top-down sequencing methods to the intact analysis of individual penaeidin isoforms.

HMGB1 is a cofactor in mammalian base excision repair

Deoxyribose phosphate (dRP) removal by DNA polymerase beta (Pol beta) is a pivotal step in base excision repair (BER). To identify BER cofactors, especially those with dRP lyase activity, we used a Pol beta null cell extract and BER intermediate as bait for sodium borohydride crosslinking. Mass spectrometry identified the high-mobility group box 1 protein (HMGB1) as specifically interacting with the BER intermediate. Purified HMGB1 was found to have weak dRP lyase activity and to stimulate AP endonuclease and FEN1 activities on BER substrates. Coimmunoprecipitation experiments revealed interactions of HMGB1 with known BER enzymes, and GFP-tagged HMGB1 was found to accumulate at sites of oxidative DNA damage in living cells. HMGB1(-/-) mouse cells were slightly more resistant to MMS than wild-type cells, probably due to the production of fewer strand-break BER intermediates. The results suggest HMGB1 is a BER cofactor capable of modulating BER capacity in cells.