Investigation of serum proteome alterations in human glioblastoma multiforme.

Glioblastoma multiforme (GBM) or grade IV astrocytoma is the most common and lethal adult malignant brain tumor. The present study was conducted to investigate the alterations in the serum proteome in GBM patients compared to healthy controls. Comparative proteomic analysis was performed employing classical 2DE and 2D-DIGE combined with MALDI TOF/TOF MS and results were further validated through Western blotting and immunoturbidimetric assay. Comparison of the serum proteome of GBM and healthy subjects revealed 55 differentially expressed and statistically significant (p <0.05) protein spots. Among the identified proteins, haptoglobin, plasminogen precursor, apolipoprotein A-1 and M, and transthyretin are very significant due to their functional consequences in glioma tumor growth and migration, and could further be studied as glioma biomarkers and grade-specific protein signatures. Analysis of the lipoprotein pattern indicated elevated serum levels of cholesterol, triacylglycerol, and low-density lipoproteins in GBM patients. Functional pathway analysis was performed using multiple software including ingenuity pathway analysis (IPA), protein analysis through evolutionary relationships (PANTHER), database for annotation, visualization and integrated discovery (DAVID), and GeneSpring to investigate the biological context of the identified proteins, which revealed the association of candidate proteins in a few essential physiological pathways such as intrinsic prothrombin activation pathway, plasminogen activating cascade, coagulation system, glioma invasiveness signaling, and PI3K signaling in B lymphocytes. A subset of the differentially expressed proteins was applied to build statistical sample class prediction models for discrimination of GBM patients and healthy controls employing partial least squares discriminant analysis (PLS-DA) and other machine learning methods such as support vector machine (SVM), Decision Tree and Naïve Bayes, and excellent discrimination between GBM and control groups was accomplished.

Mass spectral studies reveal the structure of Aß1-16-Cu2+ complex resembling ATCUN motif.

In Alzheimer's disease, copper binds to amyloid beta (Aß) peptide and generates oxidative stress. The coordination of histidine (His) residues to Cu(2+) is still uncertain. We studied Cu(2+) binding to Aß1-16 peptide using the diethyl pyrocarbonate (DEPC) assay and mass spectrometry. Our results show that only one His is involved in Cu(2+) coordination, which is identified as His6 using mass spectral studies. Novel nickel displacement studies have further supported the proposal that the Cu(2+) binding site of Aß1-16 peptide resembles the ATCUN motif of human serum albumin.

Copper binding to beta-2-microglobulin and its pre-amyloid oligomers.

Beta-2-microglobulin (beta2m) deposits as amyloid fibrils in the musculoskeletal system of patients undergoing long-term dialysis treatment as a result of kidney failure. Previous work has shown that Cu(II) binding causes beta2m to organize into nativelike dimers and tetramers that precede amyloid formation. Cu(II) is then released from higher-order oligomers before mature Cu(II)-free amyloid fibrils are formed. While some of the Cu(II)-induced structural changes that enable beta2m self-assembly are starting to be revealed, the details of how the Cu(II) binding site evolves from the monomer to the dimers and tetramers are not known. Here, we report results from three mass spectrometry (MS)-based methods that provide insight into the changing Cu-beta2m interactions. We find that monomeric beta2m binds Cu(II) via the N-terminal amine, the amide of Gln2, His31, and Asp59. In the dimer and tetramer, Asp59 is no longer bound to Cu(II), but the other residues still comprise a well-defined albeit weaker binding site that is better able to release Cu(II). Consistent with this is the observation that a fraction of the tetrameric species no longer binds Cu(II) at this weakened binding site, which agrees with a previous report that suggested the tetramer as the first Cu(II)-free oligomer. Our results also provide some insight into structural changes caused by Cu(II) binding that facilitate oligomer formation. Specifically, binding by Asp59 in the monomer requires significant movement of this residue, and we propose that this repositioning is important for establishing a pair of dimer-stabilizing salt bridges between this residue and Lys19. We also find evidence that Cu(II) binding in the N-terminal region of the monomer repels Arg3, which likely allows this residue to form a pair of dimer-stabilizing salt bridges with Glu16. Overall, our measurements suggest that the previously proposed conformational switch caused by Cu(II) binding includes not only a cis-trans isomerization at Pro32 but also the repositioning of residues that are critical for the formation of new electrostatic interactions.

Stepwise conversion of two pyrrole moieties of octaethylporphyrin to pyridin-3-ones: synthesis, mass spectral, and photophysical properties of mono and bis(oxypyri)porphyrins.

Free-base octaethylporphyrin (OEP) was converted in two steps (beta,beta'-dihydroxylation and oxidative diol cleavage with concomitant aldol condensation) to the corresponding oxypyriporphyrin. This conversion was previously described to be applicable only to the Ni(II) complex of OEP. Modified diol cleavage conditions made this reaction sequence now applicable to free-base OEP. The single-crystal structure of the resulting free-base oxypyriporphyrin was determined, proving its near-perfect planarity. The reaction sequence can also be applied to oxypyriporphyrin itself, generating the unprecedented bacteriochlorin-type bis(oxypyri)porphyrin as two separable isomers. The ground-state (UV/Vis and fluorescence spectroscopies) and excited-state (transient triplet-triplet absorption, triplet lifetimes, and triplet EPR spectroscopy) photophysical properties of all chromophores are compared with those of OEP, chlorins, and oxochlorins. The pyridone-modified porphyrins possess unique spectroscopic signatures that distinguish them from regular porphyrins or chlorins. The presence of the pyridone moiety alters the ESI(+) collision-induced fragmentation properties of these oxypyriporphyrins only to a minor degree when compared with those of OEP or chlorins, confirming their stability.

Identification of the copper(II) coordinating residues in the prion protein by metal-catalyzed oxidation mass spectrometry: evidence for multiple isomers at low copper(II) loadings.

While the Cu(II) binding sites of the prion protein have been well studied under Cu-saturation conditions, the identity of the residues involved in coordinating Cu(II) at low stoichiometries and the order in which the binding sites load with Cu(II) remain unresolved. In this study, we have used two mass spectrometry based methods to gather insight into Cu(II)-prion binding under different stoichiometric loadings of Cu(II). The first method uses metal-catalyzed oxidation reactions to site specifically modify the residues bound to Cu(II) in solution, and the second method determines Cu binding sites based on the protection of His from modification by diethyl pyrocarbonate when this residue binds Cu(II) in solution. For both methods, the residues that are labeled by these reactions can then be unambiguously identified using tandem mass spectrometry. Upon applying these two complementary methods to a construct of the prion protein that contains residues 23-28 and 57-98, several noteworthy observations are made. Coordination of Cu(II) by multiple His imidazoles is found at 1:1 and 1:2 PrP:Cu(II) ratios. Notably, there appear to be four to seven isomers of this multiple histidine coordination mode in the 1:1 complex. Furthermore, our data clearly show that His96 is the dominant Cu(II) binding ligand, as in every isomer His96 is bound to Cu(II). The individual octarepeat binding sites begin to fill at ratios of 1:3 PrP:Cu(II) with no clear preference for the order in which they load with Cu(II), although the His77 octarepeat appears to saturate last. The existence of several "degenerate" Cu binding modes at low PrP:Cu(II) ratios may allow it to more readily accept additional Cu(II) ions, thus allowing PrP to transition from a singly Cu(II) bound state to a multiply Cu(II) bound state as a function of cellular Cu(II) concentration.

Clinicopathological Analysis and Multipronged Quantitative Proteomics Reveal Oxidative Stress and Cytoskeletal Proteins as Possible Markers for Severe Vivax Malaria.

In Plasmodium vivax malaria, mechanisms that trigger transition from uncomplicated to fatal severe infections are obscure. In this multi-disciplinary study we have performed a comprehensive analysis of clinicopathological parameters and serum proteome profiles of vivax malaria patients with different severity levels of infection to investigate pathogenesis of severe malaria and identify surrogate markers of severity. Clinicopathological analysis and proteomics profiling has provided evidences for the modulation of diverse physiological pathways including oxidative stress, cytoskeletal regulation, lipid metabolism and complement cascades in severe malaria. Strikingly, unlike severe falciparum malaria the blood coagulation cascade was not found to be affected adversely in acute P. vivax infection. To the best of our knowledge, this is the first comprehensive proteomics study, which identified some possible cues for severe P. vivax infection. Our results suggest that Superoxide dismutase, Vitronectin, Titin, Apolipoprotein E, Serum amyloid A, and Haptoglobin are potential predictive markers for malaria severity.

Correction: Comprehensive Analysis of Temporal Alterations in Cellular Proteome of Bacillus subtilis under Curcumin Treatment.

[This corrects the article DOI: 10.1371/journal.pone.0120620.].

Comprehensive analysis of temporal alterations in cellular proteome of Bacillus subtilis under curcumin treatment.

Curcumin is a natural dietary compound with antimicrobial activity against various gram positive and negative bacteria. This study aims to investigate the proteome level alterations in Bacillus subtilis due to curcumin treatment and identification of its molecular/cellular targets to understand the mechanism of action. We have performed a comprehensive proteomic analysis of B. subtilis AH75 strain at different time intervals of curcumin treatment (20, 60 and 120 min after the drug exposure, three replicates) to compare the protein expression profiles using two complementary quantitative proteomic techniques, 2D-DIGE and iTRAQ. To the best of our knowledge, this is the first comprehensive longitudinal investigation describing the effect of curcumin treatment on B. subtilis proteome. The proteomics analysis revealed several interesting targets such UDP-N-acetylglucosamine 1-carboxyvinyltransferase 1, putative septation protein SpoVG and ATP-dependent Clp protease proteolytic subunit. Further, in silico pathway analysis using DAVID and KOBAS has revealed modulation of pathways related to the fatty acid metabolism and cell wall synthesis, which are crucial for cell viability. Our findings revealed that curcumin treatment lead to inhibition of the cell wall and fatty acid synthesis in addition to differential expression of many crucial proteins involved in modulation of bacterial metabolism. Findings obtained from proteomics analysis were further validated using 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) assay for respiratory activity, resazurin assay for metabolic activity and membrane integrity assay by potassium and inorganic phosphate leakage measurement. The gene expression analysis of selected cell wall biosynthesis enzymes has strengthened the proteomics findings and indicated the major effect of curcumin on cell division.

Comparative proteomics of mitosis and meiosis in Saccharomyces cerevisiae.

Precise and timely segregation of genetic material and conservation of ploidy are the two foremost requirements for survival of a eukaryotic organism. Two highly regulated cell division processes, namely mitosis and meiosis are central to achieve this objective. The modes of chromosome segregation are distinct in these two processes that generate progeny cells of equal ploidy and half the ploidy in mitosis and meiosis, respectively. Additionally, the nutritional requirement and intracellular processing of biological cue also differ in these two processes. From this, it can be envisaged that proteome of mitotic and meiotic cells will differ significantly. Therefore, identification of proteins that differ in their level of expression between mitosis and meiosis would further reveal the mechanistic detail of these processes. In the present study, we have investigated the protein expression profile of mitosis and meiosis by comparing proteome of budding yeast cultures arrested at mitotic metaphase and metaphase-I of meiosis using proteomic approach. Approximately 1000 and 2000 protein spots were visualized on 2-DE and 2D-DIGE gels respectively, out of which 14 protein spots were significant in 2-DE and 22 in 2D-DIGE (p<0.05). All the significant spots were reproducible in all biological replicates and followed the same trend. Identification of the proteins from these spots revealed that nine proteins were common in both 2-DE and 2D-DIGE. These proteins are found to be involved in various cellular processes and pathways such as cytoskeleton function and cytokinesis, carbon, nitrogen, lipid metabolism, general translation and protein folding. Among these, our further study with the cytoskeletal proteins reveals that, compared to mitosis, an up-regulation of actin cytoskeleton and its negative regulator occurs in meiosis. BIOLOGICAL SIGNIFICANCE: Mitosis and meiosis are two different types of cell division cycles with entirely different outcomes with definite biological implication for almost all eukaryotic species. In this work, we investigated, for the first time, the differential proteomic profile of Saccharomyces cerevisiae culture arrested at mitotic metaphase (M) and metaphase-I (MI) of meiosis using 2-DE and 2D-DIGE. Our findings of up-regulation of actin and its negative regulator cofilin during meiosis suggest that the rate of actin cytoskeleton turnover is more in meiosis and actin cytoskeleton may play more crucial role during meiosis compared to mitosis. Present study also suggests that actin cytoskeleton and its regulators accumulated during meiosis by forming stable protein structure even though the corresponding mRNAs are degraded as cells enter into meiosis. This is in accordance with recent studies in higher eukaryotes where actin cytoskeleton is found to play vital role during meiotic chromosome segregation. Information generated by this study is significant to reveal that even though a cell that, unlike mitosis, is metabolically inactive with no isotropic bulging of membranes as buds (in meiosis) can require more actin cytoskeleton presumably to support nuclear movements.

Mass spectrometry-based proteomics in molecular diagnostics: discovery of cancer biomarkers using tissue culture.

Accurate diagnosis and proper monitoring of cancer patients remain a key obstacle for successful cancer treatment and prevention. Therein comes the need for biomarker discovery, which is crucial to the current oncological and other clinical practices having the potential to impact the diagnosis and prognosis. In fact, most of the biomarkers have been discovered utilizing the proteomics-based approaches. Although high-throughput mass spectrometry-based proteomic approaches like SILAC, 2D-DIGE, and iTRAQ are filling up the pitfalls of the conventional techniques, still serum proteomics importunately poses hurdle in overcoming a wide range of protein concentrations, and also the availability of patient tissue samples is a limitation for the biomarker discovery. Thus, researchers have looked for alternatives, and profiling of candidate biomarkers through tissue culture of tumor cell lines comes up as a promising option. It is a rich source of tumor cell-derived proteins, thereby, representing a wide array of potential biomarkers. Interestingly, most of the clinical biomarkers in use today (CA 125, CA 15.3, CA 19.9, and PSA) were discovered through tissue culture-based system and tissue extracts. This paper tries to emphasize the tissue culture-based discovery of candidate biomarkers through various mass spectrometry-based proteomic approaches.

Serum profiling of leptospirosis patients to investigate proteomic alterations.

Leptospirosis is a zoonotic infectious disease of tropical, subtropical and temperate zones, which is caused by the pathogenic spirochetes of genus Leptospira. Although this zoonosis is generally not considered as fatal, the pathogen can eventually cause severe infection with septic shock, multi-organ failure and lethal pulmonary hemorrhages leading to mortality. In this study, we have performed a proteomic analysis of serum samples from leptospirosis patients (n=6), febrile controls (falciparum malaria) (n=8) and healthy subjects (n=18) to obtain an insight about disease pathogenesis and host immune responses in leptospiral infections. 2DE and 2D-DIGE analysis in combination with MALDI-TOF/TOF MS revealed differential expression of 22 serum proteins in leptospirosis patients compared to the healthy controls. Among the identified differentially expressed proteins, 8 candidates exhibited different trends compared to the febrile controls. Functional analysis suggested the involvement of differentially expressed proteins in vital physiological pathways, including acute phase response, complement and coagulation cascades and hemostasis. This is the first report of analysis of human serum proteome alterations in leptospirosis patients, which revealed several differentially expressed proteins, including α-1-antitrypsin, vitronectin, ceruloplasmin, G-protein signaling regulator, apolipoprotein A-IV, which have not been reported in context of leptospirosis previously. This study will enhance our understanding about leptospirosis pathogenesis and provide a glimpse of host immunological responses. Additionally, a few differentially expressed proteins identified in this study may further be investigated as diagnostic or prognostic serum biomarkers for leptospirosis. This article is part of a Special Issue entitled: Integrated omics.

Serum proteome analysis of vivax malaria: An insight into the disease pathogenesis and host immune response.

Vivax malaria is the most widely distributed human malaria resulting in 80-300 million clinical cases every year. It causes severe infection and mortality but is generally regarded as a benign disease and has not been investigated in detail. The present study aimed to perform human serum proteome analysis in a malaria endemic area in India to identify potential serum biomarkers for vivax malaria and understand host response. The proteomic analysis was performed on 16 age and gender matched subjects (vivax patients and control) in duplicate. Protein extraction protocols were optimized for large coverage of the serum proteome and to obtain high-resolution data. Identification of 67 differentially expressed and statistically significant (Student's t-test; p<0.05) protein spots was established by MALDI-TOF/TOF mass spectrometry. Many of the identified proteins such as apolipoprotein A and E, serum amyloid A and P, haptoglobin, ceruloplasmin, and hemopexin are interesting from a diagnostic point of view and could further be studied as potential serum biomarkers. The differentially expressed serum proteins in vivax malaria identified in this study were subjected to functional pathway analysis using multiple software, including Ingenuity Pathway Analysis (IPA), Protein ANalysis THrough Evolutionary Relationships (PANTHER) and Database for Annotation, Visualization and Integrated Discovery (DAVID) functional annotation tool for better understanding of the biological context of the identified proteins, their involvement in various physiological pathways and association with disease pathogenesis. Functional pathway analysis of the differentially expressed proteins suggested the modulation of multiple vital physiological pathways, including acute phase response signaling, complement and coagulation cascades, hemostasis and vitamin D metabolism pathway due to this parasitic infection. This article is part of a Special Issue entitled: Proteomics: The clinical link.

Proteomic investigation of falciparum and vivax malaria for identification of surrogate protein markers.

This study was conducted to analyze alterations in the human serum proteome as a consequence of infection by malaria parasites Plasmodium falciparum and P. vivax to obtain mechanistic insights about disease pathogenesis, host immune response, and identification of potential protein markers. Serum samples from patients diagnosed with falciparum malaria (FM) (n = 20), vivax malaria (VM) (n = 17) and healthy controls (HC) (n = 20) were investigated using multiple proteomic techniques and results were validated by employing immunoassay-based approaches. Specificity of the identified malaria related serum markers was evaluated by means of analysis of leptospirosis as a febrile control (FC). Compared to HC, 30 and 31 differentially expressed and statistically significant (p<0.05) serum proteins were identified in FM and VM respectively, and almost half (46.2%) of these proteins were commonly modulated due to both of the plasmodial infections. 13 proteins were found to be differentially expressed in FM compared to VM. Functional pathway analysis involving the identified proteins revealed the modulation of different vital physiological pathways, including acute phase response signaling, chemokine and cytokine signaling, complement cascades and blood coagulation in malaria. A panel of identified proteins consists of six candidates; serum amyloid A, hemopexin, apolipoprotein E, haptoglobin, retinol-binding protein and apolipoprotein A-I was used to build statistical sample class prediction models. By employing PLS-DA and other classification methods the clinical phenotypic classes (FM, VM, FC and HC) were predicted with over 95% prediction accuracy. Individual performance of three classifier proteins; haptoglobin, apolipoprotein A-I and retinol-binding protein in diagnosis of malaria was analyzed using receiver operating characteristic (ROC) curves. The discrimination of FM, VM, FC and HC groups on the basis of differentially expressed serum proteins demonstrates the potential of this analytical approach for the detection of malaria as well as other human diseases.

Correct identification of oxidized histidine residues using electron-transfer dissociation.

Oxidative modification to the side chain of histidine can noticeably change the collision-induced dissociation (CID) pathways of peptides containing this oxidized residue. In cases where an oxidized peptide consists two or more isomers differing only in the site of modification, oxidation to histidine usually causes the other oxidized sites to be mis-assigned in CID spectra. These spectral misassignments can sometimes be avoided by using multiple stages of MS/MS (MS(n)) or via specially optimized liquid chromatographic separation conditions. In this manuscript, we demonstrate that these misassignments can be more readily and easily avoided by using electron-transfer dissociation (ETD) to dissociate the oxidized peptides. Furthermore, we find that the relative insensitivity of ETD to side-chain chemistry allows the extent of oxidative modification to be determined readily for peptide isomers having more than one site of oxidation. The current results along with previous studies of oxidized peptides suggest that ETD is probably a better technique than CID for obtaining correct sequence and modification information for oxidized peptides.

Cu(II) organizes beta-2-microglobulin oligomers but is released upon amyloid formation.

beta-2-Microglobulin (beta2m) is deposited as amyloid fibrils in the bones and joints of patients undergoing long-term dialysis treatment as a result of kidney failure. Previous work has shown that biologically relevant amounts of Cu(II) can cause beta2m to be converted to amyloid fibrils under physiological conditions in vitro. In this work, dynamic light scattering, mass spectrometry, and size-exclusion chromatography are used to characterize the role that Cu plays in the formation of oligomeric intermediates that precede fibril formation. Cu(II) is found to be necessary for the stability of the dimer and an initial form of the tetramer. The initially formed tetramer then undergoes a structural change to a state that no longer binds Cu(II) before progressing to a hexameric state. Based on these results, we propose that the lag phase associated with beta2m fibril formation is partially accounted for by the structural transition of the tetramer that results in Cu(II) loss. Consistent with this observation is the determination that the mature beta2m amyloid fibrils do not contain Cu. Thus, Cu(II) appears to play a catalytic role by enabling the organization of the necessary oligomeric intermediates that precede beta2m amyloid formation.