Mascot Distiller Research Articles

Exploring Potential Aquaculture-Immunostimulant-Peptides Derived from Chlorella sorokiniana

Chlorella sorokiniana is a microalgae with an outstanding nutritional profile and numerous therapeutic substances that can be used as an immunostimulant, including in aquaculture. This research aimed to investigate and characterize peptides isolated from C. sorokiniana protein using TCA digestion and hydrolyzed enzymatically with trypsin. Peptides were then subsequently identified using Tandem LC-MS/MS and Mascot Distiller. Results showed that the percentage of pure protein yield following TCA digestion was 54.66%, and 12 peptides with lengths ranging from 7 to 23 sequences were discovered after trypsin digestion. These peptides originated from various enzymes and chloroplast proteins, including protein synthesis elongation factor TU, photosystem I iron-sulfur center, photosystem II 43 kDa, Ycf4, ATP-dependent zinc metalloprotease FtsH homolog, nitrate reductase, chloroplastic glucose-6-phospate dehydrogenase, and ATP synthase CF1 alpha chain. These findings demonstrated that C. sorokiniana might serve as a source of immunostimulant peptides and proteins, particularly for aquaculture biota.

Comparing Top-Down Proteoform Identification: Deconvolution, PrSM Overlap, and PTM Detection.

Generating top-down tandem mass spectra (MS/MS) from complex mixtures of proteoforms benefits from improvements in fractionation, separation, fragmentation, and mass analysis. The algorithms to match MS/MS to sequences have undergone a parallel evolution, with both spectral alignment and match-counting approaches producing high-quality proteoform-spectrum matches (PrSMs). This study assesses state-of-the-art algorithms for top-down identification (ProSight PD, TopPIC, MSPathFinderT, and pTop) in their yield of PrSMs while controlling false discovery rate. We evaluated deconvolution engines (ThermoFisher Xtract, Bruker AutoMSn, Matrix Science Mascot Distiller, TopFD, and FLASHDeconv) in both ThermoFisher Orbitrap-class and Bruker maXis Q-TOF data (PXD033208) to produce consistent precursor charges and mass determinations. Finally, we sought post-translational modifications (PTMs) in proteoforms from bovine milk (PXD031744) and human ovarian tissue. Contemporary identification workflows produce excellent PrSM yields, although approximately half of all identified proteoforms from these four pipelines were specific to only one workflow. Deconvolution algorithms disagree on precursor masses and charges, contributing to identification variability. Detection of PTMs is inconsistent among algorithms. In bovine milk, 18% of PrSMs produced by pTop and TopMG were singly phosphorylated, but this percentage fell to 1% for one algorithm. Applying multiple search engines produces more comprehensive assessments of experiments. Top-down algorithms would benefit from greater interoperability.

Antioxidant Activity of Purified Active Peptide Derived from Spirulina platensis Enzymatic Hydrolysates

The aim of this study is to isolate the antioxidative peptide from Spirulina platensis. Peptide was obtained by proteolytic digestion, ultrafiltration, fractionation by RP-HPLC, identified by LC-MS/MS—MASCOT Distiller and measured its antioxidant activity by DPPH (2.2-Diphenyl-1-picrylhydrazyl) assay. Results showed that thermolysin was the most effective enzyme to digest this algae . The active peptide Phe-Ser-Glu-Ser-Ser-Ala-Pro-Glu-Gln-His-Tyr (m/z 1281.51) was identified and synthetized, which exhibited 45.98 ± 1.7% at concentration 128.15 µg/mL. Therefore, S. platensis is indicated as a potential therapeutic source for combating oxidative stress.

P17.47 * COMPREHENSIVE PROTEOMIC PROFILING OF BEVACIZUMAB-RESISTANT GLIOBLASTOMA MULTIFORME

Drugs that impair tumour angiogenesis, i.e. therapeutic antibody anti-vascular endothelial growth factor, bevacizumab (BEV), are becoming standard therapy for recurrent GBM, despite having no impact on overall survival times. Resistance to BEV is fatal, and mechanisms are largely unexplored. With access to exceedingly rare fresh-frozen serial GBM tumours, we performed comprehensive quantitative proteome analyses to identify important mechanisms of BEV escape and tumour recurrence. Tumour tissues from three patients [primary (n = 2), recurrent (n = 2) and post-BEV recurrent (n = 3)] were homogenised, clarified (1,000 x g, 4°C) and ultracentrifuged (100,000 x g, 4°C) to isolate the soluble (SOL) proteome supernatant from the microsomal (MEM) pellet. Digested SOL and MEM proteomes were analysed by two independent quantitative MS/MS approaches; Label-free quantitation performed on spectra obtained in triplicate using an Orbitrap Velos (Thermo Electron) and 4-plex iTRAQ-labelling coupled ERLIC-RP MS/MS analysis using a 5600 TripleTOF® (AB Sciex; single run for MEM; duplicate run for SOL). Spectra were processed using Mascot Distiller, Progenesis, Scaffold and ProteinPilot™ softwares. This multi-centre proteomics project has achieved a number of highly reproducible and comprehensive quantitative proteome datasets (average of 1760 MEM proteins and 2334 SOL proteins identified at 95% confidence levels) from precious serial GBM specimens. Significant differentially abundant proteins include those involved in Rho regulation of actin-based motility and cytoskeleton and endocytosis signalling. Bioinformatics analyses with captured whole exome sequencing data are underway to define novel mechanisms of evasive resistance to BEV in recurrent GBM.

Condenser: A statistical aggregation tool for multi-sample quantitative proteomic data from Matrix Science Mascot Distiller™

We describe Condenser, a freely available, comprehensive open-source tool for merging multidimensional quantitative proteomics data from the Matrix Science Mascot Distiller Quantitation Toolbox into a common format ready for subsequent bioinformatic analysis. A number of different relative quantitation technologies, such as metabolic (15)N and amino acid stable isotope incorporation, label-free and chemical-label quantitation are supported. The program features multiple options for curative filtering of the quantified peptides, allowing the user to choose data quality thresholds appropriate for the current dataset, and ensure the quality of the calculated relative protein abundances. Condenser also features optional global normalization, peptide outlier removal, multiple testing and calculation of t-test statistics for highlighting and evaluating proteins with significantly altered relative protein abundances. Condenser provides an attractive addition to the gold-standard quantitative workflow of Mascot Distiller, allowing easy handling of larger multi-dimensional experiments. Source code, binaries, test data set and documentation are available at http://condenser.googlecode.com/.

Global Relative Quantification with Liquid Chromatography–Matrix-assisted Laser Desorption Ionization Time-of-flight (LC-MALDI-TOF)—Cross–validation with LTQ-Orbitrap Proves Reliability and Reveals Complementary Ionization Preferences

Quantitative LC-MALDI is an underrepresented method, especially in large-scale experiments. The additional fractionation step that is needed for most MALDI-TOF-TOF instruments, the comparatively long analysis time, and the very limited number of established software tools for the data analysis render LC-MALDI a niche application for large quantitative analyses beside the widespread LC-electrospray ionization workflows. Here, we used LC-MALDI in a relative quantification analysis of Staphylococcus aureus for the first time on a proteome-wide scale. Samples were analyzed in parallel with an LTQ-Orbitrap, which allowed cross-validation with a well-established workflow. With nearly 850 proteins identified in the cytosolic fraction and quantitative data for more than 550 proteins obtained with the MASCOT Distiller software, we were able to prove that LC-MALDI is able to process highly complex samples. The good correlation of quantities determined via this method and the LTQ-Orbitrap workflow confirmed the high reliability of our LC-MALDI approach for global quantification analysis. Because the existing literature reports differences for MALDI and electrospray ionization preferences and the respective experimental work was limited by technical or methodological constraints, we systematically compared biochemical attributes of peptides identified with either instrument. This genome-wide, comprehensive study revealed biases toward certain peptide properties for both MALDI-TOF-TOF- and LTQ-Orbitrap-based approaches. These biases are based on almost 13,000 peptides and result in a general complementarity of the two approaches that should be exploited in future experiments.

Activin A Suppresses Osteoblast Mineralization Capacity by Altering Extracellular Matrix (ECM) Composition and Impairing Matrix Vesicle (MV) Production

During bone formation, osteoblasts deposit an extracellular matrix (ECM) that is mineralized via a process involving production and secretion of highly specialized matrix vesicles (MVs). Activin A, a transforming growth factor-β (TGF-β) superfamily member, was previously shown to have inhibitory effects in human bone formation models through unclear mechanisms. We investigated these mechanisms elicited by activin A during in vitro osteogenic differentiation of human mesenchymal stem cells (hMSC). Activin A inhibition of ECM mineralization coincided with a strong decline in alkaline phosphatase (ALP(1)) activity in extracellular compartments, ECM and matrix vesicles. SILAC-based quantitative proteomics disclosed intricate protein composition alterations in the activin A ECM, including changed expression of collagen XII, osteonectin and several cytoskeleton-binding proteins. Moreover, in activin A osteoblasts matrix vesicle production was deficient containing very low expression of annexin proteins. ECM enhanced human mesenchymal stem cell osteogenic development and mineralization. This osteogenic enhancement was significantly decreased when human mesenchymal stem cells were cultured on ECM produced under activin A treatment. These findings demonstrate that activin A targets the ECM maturation phase of osteoblast differentiation resulting ultimately in the inhibition of mineralization. ECM proteins modulated by activin A are not only determinant for bone mineralization but also possess osteoinductive properties that are relevant for bone tissue regeneration.

Large-scale Identification of Endogenous Secretory Peptides Using Electron Transfer Dissociation Mass Spectrometry

Mass spectrometry-based unbiased analysis of the full complement of secretory peptides is expected to facilitate the identification of unknown biologically active peptides. However, tandem MS sequencing of endogenous peptides in their native form has proven difficult because they show size heterogeneity and contain multiple internal basic residues, the characteristics not found in peptide fragments produced by in vitro digestion. Endogenous peptides remain largely unexplored by electron transfer dissociation (ETD), despite its widespread use in bottom-up proteomics. We used ETD, in comparison to collision induced dissociation (CID), to identify endogenous peptides derived from secretory granules of a human endocrine cell line. For mass accuracy, both MS and tandem MS were analyzed on an Orbitrap. CID and ETD, performed in different LC-MS runs, resulted in the identification of 795 and 569 unique peptides (ranging from 1000 to 15000 Da), respectively, with an overlap of 397. Peptides larger than 3000 Da accounted for 54% in CID and 46% in ETD identifications. Although numerically outperformed by CID, ETD provided more extensive fragmentation, leading to the identification of peptides that are not reached by CID. This advantage was demonstrated in identifying a new antimicrobial peptide from neurosecretory protein VGF (non-acronymic), VGF[554-577]-NH2, or in differentiating nearly isobaric peptides (mass difference less than 2 ppm) that arise from alternatively spliced exons of the gastrin-releasing peptide gene. CID and ETD complemented each other to add to our knowledge of the proteolytic processing sites of proteins implicated in the regulated secretory pathway. An advantage of the use of both fragmentation methods was also noted in localization of phosphorylation sites. These findings point to the utility of ETD mass spectrometry in the global study of endogenous peptides, or peptidomics.

MS Data Miner: A web‐based software tool to analyze, compare, and share mass spectrometry protein identifications

Data processing and analysis of proteomics data are challenging and time consuming. In this paper, we present MS Data Miner (MDM) (http://sourceforge.net/p/msdataminer), a freely available web-based software solution aimed at minimizing the time required for the analysis, validation, data comparison, and presentation of data files generated in MS software, including Mascot (Matrix Science), Mascot Distiller (Matrix Science), and ProteinPilot (AB Sciex). The program was developed to significantly decrease the time required to process large proteomic data sets for publication. This open sourced system includes a spectra validation system and an automatic screenshot generation tool for Mascot-assigned spectra. In addition, a Gene Ontology term analysis function and a tool for generating comparative Excel data reports are included. We illustrate the benefits of MDM during a proteomics study comprised of more than 200 LC-MS/MS analyses recorded on an AB Sciex TripleTOF 5600, identifying more than 3000 unique proteins and 3.5 million peptides.

Peptide and Protein Quantitation by Acid-Catalyzed 18O-Labeling of Carboxyl Groups

We have developed a new method that applies acidic catalysis with hydrochloric acid for (18)O-labeling of peptides at their carboxyl groups. With this method, peptides get labeled at their C-terminus, at Asp and Glu residues, and at carboxymethylated cysteine residues. Oxygen atoms at phosphate groups of phosphopeptide are not exchanged. Our elaborated labeling protocol is easy to perform, fast (5 h and 30 min), and results in 95-97 atom % incorporation of (18)O at carboxyl groups. Undesired side reactions, such as deamidation or peptide hydrolysis, occur only at a very low level under the conditions applied. In addition, data analysis can be performed automatically using common software tools, such as Mascot Distiller. We have demonstrated the capability of this method for the quantitation of peptides as well as for phosphopeptides.

Isolation and determination of the primary structure of a lectin protein from the serum of the American alligator (Alligator mississippiensis)

Mass spectrometry in conjunction with de novo sequencing was used to determine the amino acid sequence of a 35kDa lectin protein isolated from the serum of the American alligator that exhibits binding to mannose. The protein N-terminal sequence was determined using Edman degradation and enzymatic digestion with different proteases was used to generate peptide fragments for analysis by liquid chromatography tandem mass spectrometry (LC MS/MS). Separate analysis of the protein digests with multiple enzymes enhanced the protein sequence coverage. De novo sequencing was accomplished using MASCOT Distiller and PEAKS software and the sequences were searched against the NCBI database using MASCOT and BLAST to identify homologous peptides. MS analysis of the intact protein indicated that it is present primarily as monomer and dimer in vitro. The isolated 35kDa protein was ~98% sequenced and found to have 313 amino acids and nine cysteine residues and was identified as an alligator lectin. The alligator lectin sequence was aligned with other lectin sequences using DIALIGN and ClustalW software and was found to exhibit 58% and 59% similarity to both human and mouse intelectin-1. The alligator lectin exhibited strong binding affinities toward mannan and mannose as compared to other tested carbohydrates.

Uncovering the Proteome Response of the Master Circadian Clock to Light Using an AutoProteome System

In mammals, the suprachiasmatic nucleus (SCN) is the central circadian pacemaker that governs rhythmic fluctuations in behavior and physiology in a 24-hr cycle and synchronizes them to the external environment by daily resetting in response to light. The bilateral SCN is comprised of a mere ~20,000 neurons serving as cellular oscillators, a fact that has, until now, hindered the systematic study of the SCN on a global proteome level. Here we developed a fully automated and integrated proteomics platform, termed AutoProteome system, for an in-depth analysis of the light-responsive proteome of the murine SCN. All requisite steps for a large-scale proteomic study, including preconcentration, buffer exchanging, reduction, alkylation, digestion and online two-dimensional liquid chromatography-tandem MS analysis, are performed automatically on a standard liquid chromatography-MS system. As low as 2 ng of model protein bovine serum albumin and up to 20 μg and 200 μg of SCN proteins can be readily processed and analyzed by this system. From the SCN tissue of a single mouse, we were able to confidently identify 2131 proteins, of which 387 were light-regulated based on a spectral counts quantification approach. Bioinformatics analysis of the light-inducible proteins reveals their diverse distribution in different canonical pathways and their heavy connection in 19 protein interaction networks. The AutoProteome system identified vasopressin-neurophysin 2-copeptin and casein kinase 1 delta, both of which had been previously implicated in clock timing processes, as light-inducible proteins in the SCN. Ras-specific guanine nucleotide-releasing factor 1, ubiquitin protein ligase E3A, and X-linked ubiquitin specific protease 9, none of which had previously been implicated in SCN clock timing processes, were also identified in this study as light-inducible proteins. The AutoProteome system opens a new avenue to systematically explore the proteome-wide events that occur in the SCN, either in response to light or other stimuli, or as a consequence of its intrinsic pacemaker capacity.

The use of a novel quantitation strategy based on Reductive Isotopic Di-Ethylation (RIDE) to evaluate the effect of glufosinate on the unicellular algae Ostreococcus tauri

We report a novel stable-isotope labeling strategy for quantitative proteomics analysis. The method consists of labeling N-termini and lysine ε-amino groups through reductive amination using acetaldehyde. This allows isotope labeling using pairs of either 2H/1H or 13C/12C without mass spectrum overlap. Our labeling procedure, which is significantly different than that developed for dimethylation, can be completed with little trace of partial ethylation; non-labeled peptides represent less than 0.05% of all peptides. Co-elution of both isotopic 13C/12C peptide pairs was observed in all cases, simplifying data analysis, which can be performed using standard commercial software such as Mascot Distiller. A 13C/12C labeled mix in a 1:1 ratio from a complex extract digest of the unicellular algae Ostreococcus tauri, showed a relative standard deviation of less than 14%. This quantitative method was used to characterize O. tauri in the presence of glufosinate, an herbicide which inhibits glutamine synthetase. Blocking glutamine synthetase significantly reduced the expression of several enzymes and transporters involved in nitrogen assimilation and the expression of a number of proteins involved in various stresses including oxidative damage response were up-regulated.

Quantitative Time-course Profiling of Parasite and Host Cell Proteins in the Human Malaria Parasite Plasmodium falciparum

Studies of the Plasmodium falciparum transcriptome have shown that the tightly controlled progression of the parasite through the intra-erythrocytic developmental cycle (IDC) is accompanied by a continuous gene expression cascade in which most expressed genes exhibit a single transcriptional peak. Because the biochemical and cellular functions of most genes are mediated by the encoded proteins, understanding the relationship between mRNA and protein levels is crucial for inferring biological activity from transcriptional gene expression data. Although studies on other organisms show that <50% of protein abundance variation may be attributable to corresponding mRNA levels, the situation in Plasmodium is further complicated by the dynamic nature of the cyclic gene expression cascade. In this study, we simultaneously determined mRNA and protein abundance profiles for P. falciparum parasites during the IDC at 2-hour resolution based on oligonucleotide microarrays and two-dimensional differential gel electrophoresis protein gels. We find that most proteins are represented by more than one isoform, presumably because of post-translational modifications. Like transcripts, most proteins exhibit cyclic abundance profiles with one peak during the IDC, whereas the presence of functionally related proteins is highly correlated. In contrast, the abundance of most parasite proteins peaks significantly later (median 11 h) than the corresponding transcripts and often decreases slowly in the second half of the IDC. Computational modeling indicates that the considerable and varied incongruence between transcript and protein abundance may largely be caused by the dynamics of translation and protein degradation. Furthermore, we present cyclic abundance profiles also for parasite-associated human proteins and confirm the presence of five human proteins with a potential role in antioxidant defense within the parasites. Together, our data provide fundamental insights into transcript-protein relationships in P. falciparum that are important for the correct interpretation of transcriptional data and that may facilitate the improvement and development of malaria diagnostics and drug therapy.

Architecture of a Full-length Retroviral Integrase Monomer and Dimer, Revealed by Small Angle X-ray Scattering and Chemical Cross-linking

We determined the size and shape of full-length avian sarcoma virus (ASV) integrase (IN) monomers and dimers in solution using small angle x-ray scattering. The low resolution data obtained establish constraints for the relative arrangements of the three component domains in both forms. Domain organization within the small angle x-ray envelopes was determined by combining available atomic resolution data for individual domains with results from cross-linking coupled with mass spectrometry. The full-length dimer architecture so revealed is unequivocally different from that proposed from x-ray crystallographic analyses of two-domain fragments, in which interactions between the catalytic core domains play a prominent role. Core-core interactions are detected only in cross-linked IN tetramers and are required for concerted integration. The solution dimer is stabilized by C-terminal domain (CTD-CTD) interactions and by interactions of the N-terminal domain in one subunit with the core and CTD in the second subunit. These results suggest a pathway for formation of functional IN-DNA complexes that has not previously been considered and possible strategies for preventing such assembly.

Differential proteomic analysis of the brain synaptic plasma membrane proteins from DHA‐deficient and adequate mice using 16O/18O labeling

Polyunsaturated fatty acids, especially docosahexenoic acid (DHA, 22:6n‐3) plays an important role in normal brain development in mammals. DHA promotes hippocampal neurite growth and synaptogenesis while DHA‐ deficiency causes impairments in hippocampus‐dependent learning and memory. In this study, we compared the synaptic plasma membrane (SPM) proteins obtained from DHA‐adequate and deficient mice using 16O/18O labeling to provide insights into the role of DHA in synaptic protein expression and function. Synaptosomal preparations from DHA‐deficient and adequate mice cortex were subjected to osmotic shock to obtain SPM. The SPM fraction was analysed by SDS‐PAGE coupled to nanoLC‐MS/MS. For quantification, we differentially labeled the peptide samples from DHA‐adequate and deficient mice using O16/O18 labeling technique. The heavy to light ratios (18O/16O) were calculated using Mascot Distiller. This strategy allowed us to detect more than 400 proteins from the SPM fraction including various receptors, kinases and transporter proteins. The 18O/16O ratios revealed differential expression of several pre‐ and postsynaptic proteins involved in neurotransmission. Some of these proteins were validated by western blot analysis. Altered levels of synaptic proteins important for synaptic transmission suggest a role of DHA in proper brain development and function.National Institutes of Health, MD.

UNiquant, a Program for Quantitative Proteomics Analysis Using Stable Isotope Labeling

Stable isotope labeling (SIL) methods coupled with nanoscale liquid chromatography and high resolution tandem mass spectrometry are increasingly useful for elucidation of the proteome-wide differences between multiple biological samples. Development of more effective programs for the sensitive identification of peptide pairs and accurate measurement of the relative peptide/protein abundance are essential for quantitative proteomic analysis. We developed and evaluated the performance of a new program, termed UNiquant, for analyzing quantitative proteomics data using stable isotope labeling. UNiquant was compared with two other programs, MaxQuant and Mascot Distiller, using SILAC-labeled complex proteome mixtures having either known or unknown heavy/light ratios. For the SILAC-labeled Jeko-1 cell proteome digests with known heavy/light ratios (H/L = 1:1, 1:5, and 1:10), UNiquant quantified a similar number of peptide pairs as MaxQuant for the H/L = 1:1 and 1:5 mixtures. In addition, UNiquant quantified significantly more peptides than MaxQuant and Mascot Distiller in the H/L = 1:10 mixtures. UNiquant accurately measured relative peptide/protein abundance without the need for postmeasurement normalization of peptide ratios, which is required by the other programs.

Axonal Transport Proteomics Reveals Mobilization of Translation Machinery to the Lesion Site in Injured Sciatic Nerve

Investigations of the molecular mechanisms underlying responses to nerve injury have highlighted the importance of axonal transport systems. To obtain a comprehensive view of the protein ensembles associated with axonal transport in injured axons, we analyzed the protein compositions of axoplasm concentrated at ligatures following crush injury of rat sciatic nerve. LC-MS/MS analyses of iTRAQ-labeled peptides from axoplasm distal and proximal to the ligation sites revealed protein ensembles transported in both anterograde and retrograde directions. Variability of replicates did not allow straightforward assignment of proteins to functional transport categories; hence, we performed principal component analysis and factor analysis with subsequent clustering to determine the most prominent injury-related transported proteins. This strategy circumvented experimental variability and allowed the extraction of biologically meaningful information from the quantitative neuroproteomics experiments. 299 proteins were highlighted by principal component analysis and factor analysis, 145 of which correlate with retrograde and 154 of which correlate with anterograde transport after injury. The analyses reveal extensive changes in both anterograde and retrograde transport proteomes in injured peripheral axons and emphasize the importance of RNA binding and translational machineries in the axonal response to injury.

PWE-049 Shotgun proteomics in the discovery of biomarkers of non-alcoholic fatty liver disease: an improved methodology

<h3>Introduction</h3> Non-alcoholic fatty liver disease is a common condition affecting up to one third of the US population. The current gold standard diagnostic tool is liver biopsy, which has associated morbidity and mortality concerns, as well as sampling error and inter-observer variability problems. There is an urgent need for the discovery and validation of non-invasive markers of this disease. Many studies have taken a targeted approach, examining the utility of various biochemical and clinical markers thought to be important in the pathogenesis of this condition. Shotgun proteomics offers an untargeted tool for the discovery of protein markers in complex clinical samples. <h3>Methods</h3> Materials: 30 patients with biopsy proven NAFLD were recruited. Patients had negative viral hepatitis screens, negative autoimmune screens, normal iron stores, and were taking no hepatotoxic medications. Biochemical and anthropological measurements were also recorded. <h3>Method</h3> Serum samples were pooled into three groups (SS/NASH/NASH fibrosis, <i>F</i>_1,2, with n=7 per group). The pooled samples were immunodepleted of the top 91 most abundant proteins. Buffer exchange and lyophilisation was performed before samples were reduced alkylated then digested with trypsin. The resultant peptide mixtures were labelled with iTRAQ tags as per the manufacturers9 protocol (Applied Biosystems), and then pooled together. Sample fraction was performed using a reverse phase C18 column at high pH. A total of 88 fractions were collected and combined to 47 fractions based on the appearance of the chromatogram. The 47 fractions were analysed by LC-MS/MS (QTOF, Agilent), using an optimised LC and MS methodology. The resultant MS data were processed using MASCOT Distiller software and the IPI_human database searched for matches. Only proteins with 2 peptide identification and a MASCOT score indicative of identity were included for analysis. <h3>Results</h3> A total of 557 proteins were identified and included for analysis. Previous iTRAQ technical replicate data indicated an error range of 1.13 (±0.10)–1.37 (±0.12). Proteins with fold changes out with this range were considered significantly differentially expressed. At least 10 proteins had a fold change &gt;5 in the NASH early fibrosis group. Interestingly, several protein markers of NAFLD fibrosis previously reported in the literature were also found to be appropriately unregulated in this experiment, including α-2-macroglobulin. <h3>Conclusion</h3> Discussion iTRAQ technology is a powerful tool, allowing analysis of up to 8 different samples simultaneously. We have improved our method of sample preparation and processing to increase the number of protein identifications. The findings from this study require further validation.

Rover: A tool to visualize and validate quantitative proteomics data from different sources

Manual validation of regulated proteins found in MS-driven quantitative proteome studies is tedious. Here we present Rover (http://genesis.ugent.be/rover), a tool that facilitates this process. Rover accepts quantitative data from different sources such as MASCOT Distiller and MaxQuant and, in an intuitive environment, Rover visualizes these data such that the user can select and validate algorithm-suggested regulated proteins in the frame of the whole experiment and in the context of the protein inference problem.