Dataset Information

Accurate multiplexed proteomics at the MS2 level using the complement reporter ion cluster.

ABSTRACT: Isobaric labeling strategies, such as isobaric tags for relative and absolute quantitation (iTRAQ) or tandem mass tags (TMT), have promised to dramatically increase the power of quantitative proteomics. However, when applied to complex mixtures, both the accuracy and precision are undermined by interfering peptide ions that coisolate and cofragment with the target peptide. Additional gas-phase isolation steps, such as proton-transfer ion-ion reactions (PTR) or higher-order MS3 scans, can almost completely eliminate this problem. Unfortunately, these methods come at the expense of decreased acquisition speed and sensitivity. Here we present a method that allows accurate quantification of TMT-labeled peptides at the MS2 level without additional ion purification. Quantification is based on the fragment ion cluster that carries most of the TMT mass balance. In contrast to the use of low m/z reporter ions, the localization of these complement TMT (TMT(C)) ions in the spectrum is precursor-specific; coeluting peptides do not generally affect the measurement of the TMT(C) ion cluster of interest. Unlike the PTR or MS3 strategies, this method can be implemented on a wide range of high-resolution mass spectrometers like the quadrupole Orbitrap instruments (QExactive). A current limitation of the method is that the efficiency of TMT(C) ion formation is affected by both peptide sequence and peptide ion charge state; we discuss potential routes to overcome this problem. Finally, we show that the complement reporter ion approach allows parallelization of multiplexed quantification and therefore holds the potential to multiply the number of distinct peptides that can be quantified in a given time frame.

SUBMITTER: Wuhr M

PROVIDER: S-EPMC3771681 | biostudies-literature | 2012 Nov

REPOSITORIES: biostudies-literature

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Accurate multiplexed proteomics at the MS2 level using the complement reporter ion cluster.

Wühr Martin M Haas Wilhelm W McAlister Graeme C GC Peshkin Leonid L Rad Ramin R Kirschner Marc W MW Gygi Steven P SP

Analytical chemistry 20121025 21

Isobaric labeling strategies, such as isobaric tags for relative and absolute quantitation (iTRAQ) or tandem mass tags (TMT), have promised to dramatically increase the power of quantitative proteomics. However, when applied to complex mixtures, both the accuracy and precision are undermined by interfering peptide ions that coisolate and cofragment with the target peptide. Additional gas-phase isolation steps, such as proton-transfer ion-ion reactions (PTR) or higher-order MS3 scans, can almost ...[more]

PMID: 23098179

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Project description:Although genetic studies have identified many hundreds of loci associated with human traits and diseases, pinpointing the causal alleles remains difficult, particularly for non-coding variants. To address this challenge, we have enhanced the sensitivity and reproducibility of the massively parallel reporter assay (MPRA), adapting it to identify variants that directly modulate gene expression. We then applied it to over 29,000 single nucleotide and insertion/deletion polymorphisms from 3,965 cis-expression quantitative trait loci (eQTL). We demonstrate strong correlation between our MPRA approach and existing measures of regulatory function, and determine an approximate sensitivity of ~20% with a positive predictive value of 60-65% to detect an eQTL causal allele. We identify 842 variants showing differential expression between alleles, including 53 well-annotated variants associated with diseases and traits. Thus, we have created a resource of concrete leads for understanding the genetic basis of specific phenotypes and illustrate the promise of this kind of approach for comprehensively interrogating how non-coding polymorphism shapes human biology. The study consists of two separate MPRA experiments, a 78,958 oligo (79k study) and a 7,500 oligo library (7.5k). For each library we processed independent transfections into two lymphoblastoid cell lines; in total we completed 5 replicates of NA12878 and 3 replicates of NA19239. For the 79k library we also performed 5 replicate transfections into the hepatocarcinoma cell line HepG2. Raw data is provided as Illumina reads of the 20 bp barcode from the RNA extracted 24 hours post transfection as well as from the plasmid library used for transfection. We also provide oligo/barcode combinations from the âgfp vector in the form of a tab delimited file containing the raw sequence reads of the barcode (column 1) and genomic sequence (column 2). Processed count files are unnormalized counts for each oligo acquired by summing all barcode matches together for each replicate.

Dataset Information

Accurate multiplexed proteomics at the MS2 level using the complement reporter ion cluster.

Publications

Accurate multiplexed proteomics at the MS2 level using the complement reporter ion cluster.

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