Stable Isotope Labeled Standards for Protein Quantitation
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Solution Overview
Problem
Current methods for quantifying target molecules in complex samples, such as human plasma, face challenges due to interference from endogenous molecules, making it difficult to achieve accurate calibration and quantitation, especially in highly multiplexed assays, where the use of surrogate peptide standards can be affected by digestion variations and post-translational modifications.
Innovation Solution
The use of two different stable isotope labeled standard (SIS) molecules with distinguishable masses allows for external calibration and quality control in the same test matrix as the sample, enabling accurate quantitation by generating calibration curves and minimizing interference from endogenous molecules.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If stable isotope labeled peptide standards are used for calibration, then quantitation can be performed in complex samples, but endogenous molecules interfere with accurate calibration and quantitation
Solution Approach 1:
The patent introduces an intermediary substance - a heterologous protein with unique peptides that are not present in the test sample matrix. These intermediary peptides serve as calibration standards without suffering from endogenous interference, allowing accurate quantitation while maintaining the benefits of peptide-based standards.
Solution Approach 2:
The patent segments the calibration standard into two distinct parts: (1) a heterologous protein portion that provides unique, non-interfering peptides for calibration, and (2) the target analyte peptides of interest. This segmentation allows the calibration function to be separated from the analyte detection function, eliminating cross-interference.
2Measurement precision
If surrogate peptide standards are used, then calibration can be achieved, but digestion variations and post-translational modifications affect the accuracy
Solution Approach 1:
The heterologous protein acts as an intermediary calibration standard that undergoes the same digestion and processing conditions as the target proteins but produces distinguishable peptides. This allows the system to measure and correct for digestion variations while maintaining accurate quantitation of the target analytes.
Solution Approach 2:
The patent changes the identity parameter of the calibration standard from endogenous peptides to heterologous peptides with distinguishable sequences. This parameter change allows the calibration standard to be differentiated from target peptides during mass spectrometry analysis, enabling accurate measurement despite variations in digestion efficiency or post-translational modifications.
3Measurement precision
If whole protein or concatenated peptide standards are used, then quantitation accuracy may improve, but production time and cost increase significantly
Solution Approach 1:
The patent uses readily available heterologous proteins (such as recombinant proteins from expression systems) as calibration standards instead of requiring custom-synthesized whole protein or concatenated peptide standards. These heterologous proteins can be produced quickly and inexpensively through standard recombinant expression methods, eliminating the time-consuming and costly standard production process while maintaining quantitation accuracy.
4Measurement precision
If calibration is performed in identical matrix to test samples, then accuracy should improve, but endogenous target molecules interfere with quantitation
Solution Approach 1:
The heterologous protein serves as an intermediary calibration standard that allows calibration to be performed in the identical test sample matrix without interference from endogenous target molecules. The unique sequences of the heterologous protein ensure its peptides are distinguishable from endogenous peptides, enabling accurate calibration curves to be generated even in the presence of the target analytes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves the accuracy and precision of protein quantitation in multiplexed assays by reducing interference and allowing for direct measurement of accuracy, aligning with regulatory guidelines and enhancing method validation and standardization.
Implementation Method 1
The use of two different stable isotope labeled standard (SIS) molecules with distinguishable masses allows for external calibration and quality control in the same test matrix as the sample
Implementation Method 2
An instrument signal magnitude is detected or measured from the target molecule, the first stable isotope labeled molecule and the second stable isotope labeled molecule
Data Source
AI summary
A methodology for the precise calibration of molecule quantifying assays is disclosed. The method uses stable isotope labeled molecules with distinguishable masses to act as internal and calibration standards that are free from endogenous interference. Furthermore, stable isotope labeled molecules allows for calibration within a test matrix. In some examples, stable isotope labeled peptides are used as internal and calibration standards for mass spectrometry assays for quantification of peptide biomarkers.