Absolute Quantification of Low-Abundance Polypeptides via High-Abundance Reference
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Solution Overview
Problem
Current label-free absolute quantification techniques for polypeptides suffer from low accuracy and high variability, particularly when dealing with low-abundance polypeptides, and often provide only relative quantification ratios, making them unsuitable for precise analysis in complex samples.
Innovation Solution
The method involves using liquid chromatography/mass spectrometry (LC/MS) to analyze peptide products from samples with varying loading quantities, calculating the average or sum of MS signals for specific sets of qualified ions of high and low-abundance polypeptides, and applying a formula to determine the absolute quantity of the low-abundance polypeptide, thereby avoiding detector saturation and reducing quantification error.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If label-free absolute quantification techniques are used, then sample processing is simplified and no external standards are needed, but accuracy and precision are low with high variability
Solution Approach 1:
The patent uses a high-abundance polypeptide with known concentration as an intermediary reference substance. This internal reference allows the system to compensate for variations in sample processing, instrument response, and detection conditions, thereby achieving accurate absolute quantification of low-abundance polypeptides without requiring external standards or complex labeling procedures.
2Measurement precision
If single point calibration using protein standard is used, then absolute quantification is achieved, but quantification variability increases due to separate enzymatic digestions
Solution Approach 1:
The patent combines the sample polypeptide and the high-abundance reference polypeptide into a single mixed sample that undergoes identical enzymatic digestion and LC-MS analysis. This unified processing approach eliminates the variability introduced by separate digestions and calibration steps, while maintaining absolute quantification capability through the known concentration of the reference substance.
Solution Approach 2:
The patent utilizes the known concentration parameter of the high-abundance polypeptide as a reference to calculate the absolute quantity of the low-abundance polypeptide. By changing the analytical parameters (MS signal intensity ratios) while keeping the reference concentration fixed, the system achieves reliable absolute quantification without the variability of separate processing steps.
3Measurement precision
If high sample loading quantity is used, then detection sensitivity improves, but detector saturation occurs and quantification error increases
Solution Approach 1:
The patent applies different loading strategies to different polypeptides within the same sample. The high-abundance reference polypeptide is loaded at concentrations that optimize its signal for absolute quantification, while the low-abundance polypeptide benefits from the enhanced sensitivity provided by the high loading quantity. The reference substance acts as an internal control that remains within the linear dynamic range of the detector.
4Measurement precision
If label-based techniques are used, then absolute quantification is achieved, but additional sample processing and yield loss occur
Solution Approach 1:
The patent extracts and removes the need for external labeling reagents and complex sample processing steps by using the inherent MS signal intensity of peptide products from simple enzymatic digestion. The high-abundance polypeptide serves as an internal reference that eliminates the requirement for labeled standards, reducing sample processing complexity and yield loss while maintaining absolute quantification capability.
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 enhances the accuracy and reproducibility of polypeptide quantification across a wide dynamic range of concentrations, achieving a 16% relative standard deviation compared to existing methods, which had an 82% relative standard deviation, thereby improving the precision of low-abundance polypeptide quantification.
Implementation Method 1
analyzing peptide products of the plurality of polypeptides at a plurality of sample loading quantities using a liquid chromatography/mass spectrometry (LC/MS) technique to obtain MS signals of ions of the peptide products
Data Source
AI summary
The present invention provides methods for improved label-free absolute quantification of relatively low abundant polypeptides by liquid chromatography/mass spectrometry analysis of peptide products obtained from simple or complex polypeptide mixtures. The methods for absolute quantification include MS signals from a set of qualified ions of peptide products of a relatively high abundant polypeptide to improve quantification of a relatively low abundant polypeptide.