Tandem mass spectrometric characterization of thiol peptides modified by the chemoselective cationic sulfhydryl reagent (4-iodobutyl)triphenylphosphonium--effects of a cationic thiol derivatization on peptide fragmentation

Fixed charge chemical modifications on peptides and proteins can impact fragmentation behaviors in tandem mass spectrometry (MS/MS). In this study, we employed a thiol-specific cationic alkylation reagent, (4-iodobutyl)triphenylphosphonium (IBTP), to selectively modify cysteine thiol groups in mitochondrial proteome samples. Tandem mass spectrometric characteristics of butyltriphenylphosphonium (BTP)-modified peptides were evaluated by comparison to their carbamidomethylated (CAM) analogues using a quadrupole time-of-flight (Q-TOF) instrument under low energy collision-induced dissociation (CID) conditions. Introduction of the fixed charge modification resulted in the observation of peptide and fragment (b(n) and y(n)) ions with higher charge states than those observed for CAM-modified analogues. The charged BTP moiety had a significant effect on the neighboring amide bond fragmentation products. A decrease in relative abundances of the product ions at the corresponding cleavage sites was observed compared with those from the CAM-modified derivatives. This effect was particularly noticeable when an Xxx-Pro bond was in the vicinity of a BTP group. We hypothesized that the presence of a phosphonium moiety will reduce the tendency for protonation of the proximal amide bonds in the peptide backbone. Indeed, calculations indicated that proton affinities of backbone amide bonds close to the modified cysteine residues were generally 20-50 kcal/mol lower for BTP-modified peptides than for the unmodified or CAM-modified analogues with the sequence motif -Ala-Cys-Ala(n)-Ala(2)-, -Ala-Cys-Ala(n)-Pro-Ala-, and -Ala-Pro-Ala(n)-Cys-Ala-, n=0-3.

Solvent accessibility of betaB2-crystallin and local structural changes due to deamidation at the dimer interface

In the lens of the eye the ordered arrangement of the major proteins, the crystallins, contributes to lens transparency. Members of the beta/gamma-crystallin family share common beta-sheet rich domains and hydrophobic regions at the monomer-monomer or domain-domain interfaces. Disruption of these interfaces, due to post-translational modifications, such as deamidation, decreases the stability of the crystallins. Previous experiments have failed to define the structural changes associated with this decreased stability. Using hydrogen/deuterium exchange with mass spectrometry (HDMS), deamidation-induced local structural changes in betaB2-crystallin were identified. Deamidation was mimicked by replacing glutamines with glutamic acids at homologous residues 70 and 162 in the monomer-monomer interface of the betaB2-crystallin dimer. The exchange-in of deuterium was determined from 15 s to 24 h and the global and local changes in solvent accessibility were measured. In the wild type betaB2-crystallin (WT), only about 20% of the backbone amide hydrogen was exchanged, suggesting an overall low accessibility of betaB2-crystallin in solution. This is consistent with a tightly packed domain structure observed in the crystal structure. Deuterium levels were initially greater in N-terminal domain (N-td) peptides than in homologous peptides in the C-terminal domain (C-td). The more rapid incorporation suggests a greater solvent accessibility of the N-td. In the betaB2-crystallin crystal structure, interface Gln are oriented towards their opposite domain. When deamidation was mimicked at Gln70 in the N-td, deuterium levels increased at the interface peptide in the C-td. A similar effect in the N-td was not observed when deamidation was mimicked at the homologous residue, Gln162, in the C-td. This difference in the mutants can be explained by deamidation at Gln70 disrupting the more compact C-td and increasing the solvent accessibility in the C-td interface peptides. When deamidation was mimicked at both interface Gln, deuterium incorporation increased in the C-td, similar to deamidation at Gln70 alone. In addition, deuterium incorporation was decreased in the N-td in an outside loop peptide adjacent to the mutation site. This decreased accessibility may be due to newly exposed charge groups facilitating ionic interactions or to peptides becoming more buried when other regions became more exposed. The highly sensitive HDMS methods used here detected local structural changes in solution that had not been previously identified and provide a mechanism for the associated decrease in stability due to deamidation. Changes in accessibility due to deamidation at the interface led to structural perturbations elsewhere in the protein. The cumulative effects of multiple deamidation sites perturbing the structure both locally and distant from the site of deamidation may contribute to aggregation and precipitation during aging and cataractogenesis in the lens.

Retinal proteomic changes under different ischemic conditions - implication of an epigenetic regulatory mechanism

In retina, an ischemic injury-resistant condition (ischemic tolerance) can be induced by a sub-lethal ischemic treatment (preconditioning) prior to an otherwise injurious ischemic insult. In this work, we compared retinal proteomic changes under three different ischemic conditions, as a means to identify the effector mechanisms that underlie retinal ischemic tolerance. Transient retinal ischemia was induced by elevating the intraocular pressure (IOP) in three groups of adult rats as follows: Group 1, ischemic-preconditioned, 110 mmHg for 8 minutes followed by 48 hours reperfusion; Group 2, ischemic-injured, 110 mmHg for 60 minutes followed by 24 hours reperfusion; Group 3, ischemic-tolerant, preconditioning treatment followed by another 60 minutes of 110 mmHg and 24 hours reperfusion. Protein quantities in each of the afore-mentioned retinal ischemic conditions, as determined by quantitative mass spectrometry, were compared with that of the contralateral control eyes (sham-treated). As a result, a total of 328 proteins were identified and quantified; among them, 30-60% of proteins showed a change in abundance under one or more retinal ischemic conditions. In particular, in ischemic-tolerant retinas, histone proteins H2B, H3 and H4 demonstrated an increase in abundance, whereas histone H2A showed a decrease in abundance. Further immunohistochemical analyses confirmed the results of proteomic analyses, and detected an up regulation of tri-methylated histone H3, mono-ubiquitinated histone H2A and Polycomb group protein RING2. Together, these results suggest a role of epigenetic regulation in the induction of retinal ischemic tolerance that involves histone and polycomb proteins.

Immunomodulatory effects of holothurian triterpene glycosides on mammalian splenocytes determined by mass spectrometric proteome analysis

Spleen is a prime organ in which immuno-stimulation takes place in mammalians. Proteome analysis was used to investigate the elicited effects on mouse splenocytes upon exposure to holothurian triterpene glycosides. Cucumarioside A(2)-2, and Frondoside A, respectively, have been used to in-vitro stimulate primary splenocyte cultures. Differential protein expression was monitored by 2D gel analysis and proteins in spots of interest were identified by MALDI ToF MS and nano LC-ESI Q-ToF MS/MS, respectively. Differential image analysis of gels from control vs. gels from stimulated primary splenocyte cultures showed that approximately thirty protein spots were differentially expressed. Prime examples of differentially expressed proteins are NSFL1 cofactor p47 and hnRNP K (down-regulated), as well as Septin-2, NADH dehydrogenase [ubiquinone] iron-sulfur protein 3, and GRB2-related adaptor protein 2 (up-regulated). Immuno-analytical assays confirmed differential protein expression. Together with results from proliferation and cell adhesion assays, our results show that cellular proliferation is stimulated by holothurian triterpene glycosides. In conclusion, holothurian triterpene glycosides are thought to express their immuno-stimulatory effects by enhancing the natural cellular defense barrier that is necessary to fight pathogens and for which lymphocytes and splenocytes have to be recruited constantly due to limited lifetimes of B-cells and T-cells in the body.

Identification of Mycobacterium avium pathogenicity island important for macrophage and amoeba infection

The ability to infect macrophages is a common characteristic shared among many mycobacterial species. Mycobacterium avium, Mycobacterium tuberculosis, and Mycobacterium kansasii enter macrophages, using the complement receptors CR1, CR3, CR4, and the mannose receptor. To identify M. avium genes and host cell pathways involved in the bacterial uptake by macrophages, we screened a M. avium transposon mutant library for the inability to enter macrophages. Uptake-impaired clones were selected. Sequence of six M. avium clones identified one gene involved in glycopeptidolipid biosynthesis, one gene encoding the conserved membrane protein homologue to the M. avium subsp. paratuberculosis MAP2446c gene and four others belonging to the same region of the chromosome. Analysis of the chromosome region revealed a pathogenicity island inserted between two tRNA sequences with 58% of G+C content versus 69% in the M. avium genome. The region is unique for M. avium and is not present in M. tuberculosis or M. paratuberculosis. Although the mutants did not differ from the WT bacterium regarding the binding to macrophage cell membrane, analysis of macrophage proteins after 1 h infection revealed a deficiency in the mutant to phosphorylate certain proteins on uptake. To understand M. avium interaction with two evolutionarily distinct hosts, the mutants were evaluated for Acanthamoeba castellanii invasion. The defect in the ability of the mutants to invade both cells was highly similar, suggesting that M. avium might have evolved mechanisms that are used to enter amoebas and human macrophages.

Characterization of disulfide linkages and disulfide bond scrambling in recombinant human macrophage colony stimulating factor by fast-atom bombardment mass spectrometry of enzymatic digests

Fast-atom bombardment mass spectrometry was used to study disulfide bonding patterns in heat-denatured human recombinant macrophage colony stimulating factor (rhM-CSF). The heat-denaturated protein was studied by analysis of the pattern of peptides in the proteolytic digests. Native rhM-CSF is a homodimer with intramolecular disulfide linkages between Cys7-Cys90, Cys48-Cys139, and Cys102-Cys146 and intermolecular linkages between Cys31-Cys31, and the pairs Cys157 and Cys159. Brief heating for 1 min leads to partial disulfide bond scrambling. In addition to the native disulfide bonds between Cys7-Cys90, Cys48-Cys139, and Cys31-Cys31, nonnative disulfide bonds were detected between Cys48-Cys90 and Cys48-Cys102. When heated for 5 min the disulfide bonds of rhM-CSF are completely scrambled and lead to nonnative intramolecular disulfide bonds between Cys48-Cys102 and Cys90-Cys102 and one intermolecular disulfide bond between Cys102-Cys102.

Disulfide linkages in the in vitro refolded intermediates of recombinant human macrophage-colony-stimulating factor: analysis of the sulfhydryl alkylation of free cysteine residues by fast-atom bombardment mass spectrometry

Fast-atom bombardment mass spectrometry was used to follow the time course of disulfide bond formation during in vitro refolding of recombinant human macrophage-colony-stimulating factor. The content of iodoacetamide-alkylated half-cystines in proteolytic peptides of trapped refolding intermediates collected at 0, 6, 17, 24, and 72 hr was determined under reducing conditions. Size-exclusion high-performance liquid chromatography analyses of the collected alkylated samples indicate that aggregated monomer proceeded through a nonaggregated monomer to an intermediate dimer and finally to the fully folded and active dimer. Underalkylation was first detected by fast-atom bombardment mass spectrometry in 17-hr samples at Cys157 and Cys159 and this corresponded to the first sample containing dimer. Analyses of intermediates from subsequent time points indicated a decrease in alkylated sulfhydryls, and at 72 hr no alkylated peptide was detected. Early samples containing only monomer showed no evidence of disulfide bonds, and the occurrence of disulfide shuffling at the monomer stage could be ruled out under the highly reducing conditions used for refolding. Biological activity was not detectable in early samples but increased to 3.6% after 24 hr of refolding and to 86% of maximum at the 72-hr time point.

Assignment of the inter- and intramolecular disulfide linkages in recombinant human macrophage colony stimulating factor using fast atom bombardment mass spectrometry

The disulfide bridges in recombinant human macrophage colony stimulating factor (rhM-CSF), a 49-kDa homodimeric protein, were assigned. The 18 cysteines in the dimer form three intermolecular and two sets of three intramolecular disulfide bonds. The intermolecular disulfide bridges hold the dimer together and form symmetric bonds in which Cys31 and Cys157/Cys159 from one monomer unit are linked to the corresponding cysteines of the second monomer. The intramolecular disulfide bonds are located between Cys7-Cys90, Cys48-Cys139, and Cys102-Cys146, respectively. The resistance of native M-CSF to proteolytic cleavage was overcome by an initial chemical cleavage reaction using BrCN. The close proximity of four cysteines (Cys139, Cys146, Cys157, and Cys159) results in a tight core complex that makes the protein undigestable for most proteases. Digestion using endoprotease Asp-N resulted in cleavage at Asp156 near the C-terminal end of this region, thereby opening the complex structure.

Determination of the glycosylation patterns, disulfide linkages, and protein heterogeneities of baculovirus-expressed mouse interleukin-3 by mass spectrometry

The primary structure of mouse interleukin-3 (IL-3) expressed by recombinant baculovirus-infected silkworm (Bombyx mori) larvae was analyzed by subjecting isolated IL-3 derived peptides to liquid secondary ion mass spectrometry. Two species of IL-3 were isolated from the silkworm hemolymph by reverse-phase high-pressure liquid chromatography. The major component has M(r)20-22 x 10(3) as determined by SDS-PAGE. Liquid secondary ion mass spectrometric analysis was carried out on the reduced tryptic and endopeptidase lysyl-C peptides of glycosylated and deglycosylated IL-3. These studies provided evidence that (1) Asn-16 is heterogeneously glycosylated with four different oligosaccharides, (2) Asn-86 is either nonglycosylated or has attached to it one oligosaccharide, (3) the N-glycosylation sites Asn-44 and Asn-51 are not glycosylated, and (4) there is no O-glycosylation. Liquid secondary ion mass spectrometric analysis of the unreduced tryptic peptides provided evidence for disulfide linkages between Cys-140 and Cys-79 or Cys-80 and between Cys-17 and Cys-79 or Cys-80. In comparison to the major component, a minor IL-3 species (M(r) 17-19 x 10(3) by SDS-PAGE) isolated from the hemolymph showed no difference with respect to the glycosylation pattern or the disulfide linkages, but it was cleaved between Ala-127 and Ser-128, and only a disulfide linkage between Cys-140 and Cys-79 or Cys-80 held the molecule together.(ABSTRACT TRUNCATED AT 250 WORDS)

Liquid secondary ion mass spectrometry analysis of permethylated, n-hexylamine derivatized oligosaccharides. Application to baculovirus expressed mouse interleukin-3

Reductive amination with n-hexylamine followed by permethylation was used as a procedure for the liquid secondary ion mass spectrometry (LSIMS) analysis of Asn-linked oligosaccharides. Initial experiments with this procedure were performed on maltoheptaose. These experiments show that exhaustive methylation at the newly formed secondary nitrogen forms a quaternary ammonium salt. When this is subjected to positive ion LSIMS, an abundant M(+) ion is observed. This procedure was applied to the Asn-linked oligosaccharides released from human transferrin and ribonuclease-B. The reductively aminated, permethylated mixture of oligosaccharides from ribonuclease-B afforded a positive ion LSI mass spectrum in which M(+) ions for Mans5-9GlcNAc2 could be assigned. The positive ion LSI mass spectrum obtained from the mixture of oligosaccharides isolated from human transferrin showed M(+) ions that could be assigned to both monosialylated and disialylated biantennary complex type oligosaccharides. Reductive amination followed by permethylation of the Asn-linked oligosaccharides isolated from baculovirus expressed mouse interleukin-3 produced in Bombyx mori gave a positive ion LSI mass spectrum in which the oligosaccharides could be assigned the monosaccharide composition Man2-4[Fuc]GlcNAc2 and Man2GlcNAc2. These are believed to be dimannose, trimannose, and tetramannose chitobiose core oligosaccharides, three of which are fucosylated.

Aspirin improves the patency rate of seeded vena cava grafts

The purpose of this study was to evaluate the effectiveness of aspirin (ASA) and porcine endothelial cell seeding in improving the patency rate of vena cava grafts. Thirty-nine dogs underwent infrarenal vena cava replacement by 10 cm lengths of 8 mm I.D. ringed polytetrafluoroethylene grafts. Thirty-one grafts were seeded with 1-1.5 x 10(6) porcine aortic endothelial cells while eight were not (GIII). Of the seeded group, 16 animals received no ASA (GI), while 15 others (GII) were given ASA (325 mg) daily starting two days preoperatively and continuing until sacrifice. Venograms were performed on the fourth postoperative day. Grafts were harvested 32 days after insertion and evaluated for patency rate and endothelialized surfaces. The 32-day patency rate was significantly higher for GII than for GI and III animals (67% vs. 13 and 25% respectively). Endothelialized surface was higher in GII than Gi and III (67% vs. 16% and 18% respectively). We conclude that endothelial cell seeding alone does not prevent graft closure and that a combination of ASA and cell seeding significantly increases the patency rate of vena cava grafts.

Evidence for radical anion formation during liquid secondary ion mass spectrometry analysis of oligonucleotides and synthetic oligomeric analogues: a deconvolution algorithm for molecular ion region clusters

It is shown that one-electron reduction is a common process that occurs in negative ion liquid secondary ion mass spectrometry (LSIMS) of oligonucleotides and synthetic oligonucleosides and that this process is in competition with proton loss. Deconvolution of the molecular anion cluster reveals contributions from (M-2H).-, (M-H)-, M.-, and (M + H)-. A model based on these ionic species gives excellent agreement with the experimental data. A correlation between the concentration of species arising via one-electron reduction [M.- and (M + H)-] and the electron affinity of the matrix has been demonstrated. The relative intensity of M.- is mass-dependent; this is rationalized on the basis of base-stacking. Base sequence ion formation is theorized to arise from M.- radical anion among other possible pathways.

Effect of preclotting and precoating agents on seeded venous grafts

This study evaluated the effect of whole blood preclotting (WB), fibronectin (FB) and "Cell Tak" (CT) precoating on the patency rate of seeded vena cava grafts. Ten cm x 8 mm ID ringed PTFE grafts were implanted in the vena-cavae of 29 dogs. Aspirin (325 mg po qd) was administered pre-operatively and continued post-operatively. After preclotting or precoating, all grafts were seeded with porcine endothelial cells. The 32 day patency rates were: 67%, 67% and 37% for WB, FB and CT, respectively (p less than 0.5 CT vs FB, WB). Endothelialized surfaces ranged from 67 +/- 35, 43 +/- 41 to 28 +/- 45% respectively for WB, FB and CT (p less than 0.05 CT vs WB). Preclotting time was shortest for WB technique. We conclude that: 1) FB and WB grafts have the highest patency rate with WB preclotting being a more cost effective and less time consuming technique; 2) endothelial seeding and Aspirin may make vena cava grafting possible.

Acute radiation injury of mice and the influence of sudden time shift

The daily light-dark regimen for two groups of mice was advanced by 8 hr. A third group remained in unchanged lighting conditions. At seven different times within the following day subgroups of the time-shifted mice as well as of the group with unchanged time schedule were exposed to whole-body X irradiation. Mortality, body weight, and temperature of each animal were registered for 30 days following exposure and were regarded as indicators of radiation response. Radioresistance was found to be highest after two-thirds of the daily light span, confirming earlier reports by other authors. Well-defined effects of time shift and a corresponding shift of the maximum of radioresistance could be demonstrated. With the individual body weight as an independent variable, mathematical formulas for survival prognosis could be established.

Chronobiologic serial sections of several orders

The chronobiologic serial section is described. Its applicability to the analysis of nonequidistant data is emphasized. Its ability to detect and quantify multiple components is discussed and exemplified on simulated series with various amounts of additive Gaussian noise. This least-squares method is discussed in the context of a number of complementary procedures such as complex demodulation and linear-nonlinear least-squares rhythmometry.

The determination of polychlorodibenzo-p-dioxins in pentachlorophenol and wood treatment solutions

Analytical methods have been implemented to measure levels of polychlorodibenzo-p-dioxins, and polychlorodibenzofurans in pentachlorophenol solutions used in the Boulton wood treatment process. When normalized against the pentachlorophenol (PCP) content, the octachlorodibenzo-p-dioxin level was 34% higher in the recirculating PCP solution than in the fresh PCP solution, and in the sludge it was 90% higher. A smaller concentration increase was observed for the heptachlorodibenzo-p-dioxin in the recirculating solution, but a similar increase was observed in the sludge.

Methylmercury: effect on serum enzymes and humoral antibody

Dosages of 20 and 10 ppm methylmercury were toxic to rabbits while 1 ppm did not produce clinical signs or death. Serum alkaline phosphatase levels were elevated in all rabbits exposed to methylmercury. Methylmercury-exposed rabbits challenged to A/PR8 influenza virus had hemagglutination inhibition titers as much as four times lower than those of controls. Histopathologic lesions were found in the cerebellum of rabbits that died. The most significant features of this study were that methylmercury chloride suppressed the humoral immune system and resulted in increased serum alkaline phosphatase levels, which may aid in diagnosis when methylmercury poisoning is suspected.

Rat parietal yolk sac basement membrane. An investigation of the antigenic determinants using a radioimmunoassay

Previous studies have shown that there is microscopic and biochemical evidence that rat parietal yolk sac synthesizes basement membrane (type IV) collagen; this study shows that a radioimmunoassay may be used for the detection of type IV collagen in such biosynthetic systems. Rat parietal yolk sacs incubated in medium containing (14C) proline either with or without alphaalpha-dipyridyl produced either unhydroxylated or hydroxylated (14C)collagen. The immunological reactivity of these two preparations was investigated using antibodies to bovine type IV collagen in a radioimmunoassay which demonstrated that the hydroxylated (14C)collagen preparation had a considerably higher level of antigenicity than the unhydroxylated (14C)collagen. Hydroxylated rat type IV (14C)collagen which had been reduced and alkylated was intermediate in antigenicity between hydroxylated and unhydroxylated material. These findings suggest that there are antigenic determinants which depend upon hydroxylation of the collagen molecule, and others dependent upon intact disulphide bonds. In addition, various levels of pepsin extracted unlabelled calf anterior lens capsule collagen caused inhibition of antibody binding to (14C)collagen. Rat type IV (14C)collagen which had been digested with collagenase was inactive in the radioimmunoassay, while pepsin digestion caused no reduction in antigenicity. These findings suggest that the antiserum is directed towards the collagenous part of the molecule and may be a useful tool in the detection of biosynthesized basement membrane collagen.