EpiTag™ Technology

The EpiTag™ technology platform enables quantitative, multiplexed and highly specific measurements of protein abundance and amounts of phosphorylation at specific sites using targeted antibody pairs in a peptide-based measurement format. By measuring peptides as surrogates for whole proteins, both the total amount and phosphorylation levels of targets are measured simultaneously. EpiTag™ peptide standards are used for absolute, quantitative readouts.

EpiTag™ technology uses computational algorithms to identify unique, continuous linear sequences (EpiTag™ Sequences) in proteins. EpiTag™ antibodies generated against EpiTag™ sequences have pre-defined target specificity. Protein abundance and/or protein phosphorylation measurements are made at the peptide level, using EpiTag™ antibodies, following proteolytic fragmentation of samples and liberation of EpiTag-bearing peptides (see Figure). EpiTag™ capture antibodies (red, dark purple in Figure below) are incorporated onto arrays (beads, planar surfaces) and bind the peptide fragments containing the targeted EpiTag™ site. A second detection antibody (blue, light purple), directed against either another EpiTag™ sequence or a phosphospecific motif, completes the “sandwich immunoassay.”

EpiTag™ technology is distinguished by:

  • absolute quantitation using EpiTag™ peptide standards,
  • site-specific phosphorylation measurements,
  • simultaneous measurements of total protein and phosphorylation levels in a single assay,
  • high assay specificity,
  • broad multiplexing capabilities.


EpiTag™ technology is incorporated into two distinct product lines:


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Q-SONAR™ Discovery

Epitome’s Mass Spectrometry-based Discovery Platform, Q-SONAR™, provides broad, quantitative phosphorylation profiling of cells and/or tissues for informed decision making at multiple stages during drug discovery and development. Q-SONAR™ capitalizes on the value derived from elucidating biology by making measurements that identify important biomarkers, new drug targets and key signaling nodes associated with drug mechanisms of action to support effective compound assessments.

By examining hundreds of dynamic tyrosine phosphorylation events across cell signaling networks on a global scale, critical changes and pathway associations are revealed and mass spec phosphopeptide ‘signatures’ or ‘fingerprints’ are generated. These signatures represent real-time readouts of a cell’s or tissue’s physiological state and can be used to show changes in response to disease, drug treatments or other conditions.

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