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PhosFox: a bioinformatics tool for peptide-level processing of LC-MS/MS-based phosphoproteomic data.

ABSTRACT: BACKGROUND:It is possible to identify thousands of phosphopeptides and -proteins in a single experiment with mass spectrometry-based phosphoproteomics. However, a current bottleneck is the downstream data analysis which is often laborious and requires a number of manual steps. RESULTS:Toward automating the analysis steps, we have developed and implemented a software, PhosFox, which enables peptide-level processing of phosphoproteomic data generated by multiple protein identification search algorithms, including Mascot, Sequest, and Paragon, as well as cross-comparison of their identification results. The software supports both qualitative and quantitative phosphoproteomics studies, as well as multiple between-group comparisons. Importantly, PhosFox detects uniquely phosphorylated peptides and proteins in one sample compared to another. It also distinguishes differences in phosphorylation sites between phosphorylated proteins in different samples. Using two case study examples, a qualitative phosphoproteome dataset from human keratinocytes and a quantitative phosphoproteome dataset from rat kidney inner medulla, we demonstrate here how PhosFox facilitates an efficient and in-depth phosphoproteome data analysis. PhosFox was implemented in the Perl programming language and it can be run on most common operating systems. Due to its flexible interface and open source distribution, the users can easily incorporate the program into their MS data analysis workflows and extend the program with new features. PhosFox source code, implementation and user instructions are freely available from https://bitbucket.org/phintsan/phosfox. CONCLUSIONS:PhosFox facilitates efficient and more in-depth comparisons between phosphoproteins in case-control settings. The open source implementation is easily extendable to accommodate additional features for widespread application use cases.

SUBMITTER: Soderholm S

PROVIDER: S-EPMC4098950 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature

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Project description:Human keratinocytes, HaCaT cells were transfected with the dsRNA-analogue polyinosinic-polycytidylic acid (poly I:C) (Sigma-Aldrich) using Lipofectamine 2000 reagent (Invitrogen) for intracellular delivery. The cells were transfected with 7 ug/ml poly I:C for 1 h or left untreated. The cells were collected in PBS with a cell scraper and washed once with PBS before they were lysed with HEPES lysis buffer (50 mM HEPES, 150 mM NaCl, 1 mM EDTA, 1 % NP-40, pH 7.4) including protease and phosphatase inhibitor cocktails (Sigma-Aldrich). The cell lysates were centrifuged 2,264 x g for 15 min at 4°C, divided into smaller fractions and centrifuged again 11,686 x g for 15 min at 4°C . The supernatant was collected and the protein content was measured with Bio-Rad DC protein assay (Bio-Rad). For the samples, 8 mg of protein was used. The proteins were precipitated with 10 % TCA/acetone at -20°C overnight. Samples were centrifuged 10,733 x g for 20 min at 4°C and the supernatant was removed. The precipitation was washed once with acetone and dissolved in urea buffer (8 M urea, 400 mM NH4CO3, 20 mM DL-dithiotheitol, 1 mM EDTA, pH 8.5). The proteins were reduced, alkylated, and enzymatically digested in-solution with lysyl endopeptidase (Wako Chemicals) and trypsin (Promega). The peptides were fractionated by strong cation exchange chromatography. Phosphopeptide enrichment was performed with immobilized-metal affinity chromatography (IMAC) using PHOS-Select Iron Affinity Gel (Sigma Aldrich). The enriched phosphopeptides were analyzed by nanoLC-MS/MS using an Ultimate 3000 nano-LC (Dionex) coupled to a QSTAR Elite hybrid quadrupole TOF-MS (Applied Biosystems/MDS Sciex) with nano-ESI ionization.23,24 The LC-MS/MS data were submitted through the ProteinPilot 4.0 interface (Applied Biosystems/MDS Sciex) to an in-house Mascot database search engine version 4.0 (Matrix Science), and to the ProteinPilot algorithm Paragon. The data were searched against the human canonical sequences in the Swiss-Prot database (decoy version 08132012 for the Mascot searches and version 04012013 with 539,829 sequences for the Paragon searches). The Mascot search criteria were: fixed modifications: carbamidomethyl of cysteine, variable modifications: oxidation (M), phospho (ST), phospho (Y), acetylation (K), 1 missed cleavage allowed, enzyme: trypsin. The Paragon search criteria were: modifications: cystein alkylation with iodoacetamide, ID focus: biological modifications, phosphorylation emphasis, identification threshold: 95 % confidence (Unused ProtScore (Conf) > 1.3), Thorough search (ID), enzyme: trypsin.

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PhosFox: a bioinformatics tool for peptide-level processing of LC-MS/MS-based phosphoproteomic data.

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