Modified Peptide Quantification via Synthetic Reference Standards
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Solution Overview
Problem
Current methods for quantifying phosphorylated peptides in biological samples are limited by their inability to provide unbiased, comprehensive, and accurate measurements, especially in primary tissues, due to requirements for large cell numbers, low throughput, and practical challenges with chemical labeling and isotope synthesis.
Innovation Solution
A method involving the preparation of a database of modified peptides and comparison with biological sample data using mass spectrometry and computer programming, which includes obtaining peptides, adding reference modified peptides, enriching and analyzing them via LC-MS/MS, and normalizing data using a computer program like PESCAL for identification and quantification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If metabolic labelling with stable isotopes (SILAC) is used to quantify phosphorylation sites, then quantification of hundreds to thousands of phosphorylation sites is achieved, but the approach cannot be used in primary tissues and has low throughput
Solution Approach 1:
The patent uses synthetic peptide copies as internal standards instead of requiring metabolic labeling of entire cells. These synthesized reference peptides replicate the exact mass and chemical properties of target phosphorylated peptides, enabling direct comparison and quantification without the need for cell culture or metabolic activity
Solution Approach 2:
The patent performs preliminary synthesis and characterization of reference phosphorylated peptides before the actual quantification experiment. This pre-prepared database of reference peptides with known masses and sequences allows for rapid subsequent quantification across multiple samples without repeating the labeling process
2Measurement precision
If isotope labelled internal standard peptides are synthesized to measure phosphorylated peptides, then quantification is possible, but the synthesis of thousands of phosphorylated peptides labelled with stable isotopes is not possible in practice
Solution Approach 1:
The patent uses commercially available synthetic peptide synthesis methods to create reference standards that are simpler and more economical than stable isotope labeling. These synthetic peptides serve as disposable reference materials that can be readily produced without complex isotopic enrichment processes
Solution Approach 2:
The patent changes the approach from modifying existing peptides with heavy isotopes to synthesizing reference peptides with naturally occurring amino acids but known precise masses. This parameter change in the synthesis strategy makes the production of thousands of reference peptides practically feasible
3Measurement precision
If chemical labeling (iTRAQ) is used to label peptides with stable isotopes, then relative quantification of peptides is achieved, but the number of samples that can be compared is limited and chemical labelling introduces variability
Solution Approach 1:
The patent extracts the quantification function from complex chemical labeling reactions and isolates it to simple mass comparison of synthetic reference peptides against sample peptides. This removes the limiting factor of labeling chemistry capacity while maintaining accurate relative quantification through direct mass spectral intensity comparison
Solution Approach 2:
The patent introduces synthetic reference peptides as intermediary standards that mediate the quantification process. These reference peptides serve as a bridge between the sample peptides and the quantification algorithm, eliminating the need for multi-plexed chemical labels and enabling unlimited sample comparison
4Measurement precision
If chemical labeling is performed to quantify peptides, then quantification is achieved, but variability is introduced at the chemical reaction step
Solution Approach 1:
The patent eliminates the need for external chemical labeling reactions by using synthetic reference peptides that inherently possess the exact mass and chemical properties needed for comparison. The reference peptides self-serve as internal standards without requiring additional chemical modification steps that could introduce variability
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
Enables the simultaneous quantification of thousands of modified peptides, including phosphorylated ones, with high sensitivity and throughput, allowing for the analysis of signaling pathways without the need for extensive cell growth or identification by tandem mass spectrometry, and the ability to compare an unlimited number of samples.
Implementation Method 1
a sample is loaded onto the MS instrument and compounds present in this sample are ionized
Implementation Method 2
Mass spectrometry (MS) is an analytical technique that measures the mass to charge (m/z) ratio of the ions formed
Implementation Method 3
The combination of MS with the physical separation technique of liquid chromatography is known as liquid chromatography-mass spectrometry (LC-MS)
Implementation Method 4
compounds present in this sample are ionized, for example by electrospray ionization (ESI)
Data Source
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AI summary
The present invention provides a method for quantifying modified peptides in a sample, the method comprising: (a) obtaining peptides from the sample; (b) adding reference modified peptides to the peptides obtained in step (a) to produce a mixture of peptides and reference modified peptides; (c) carrying out mass spectrometry (MS) on said mixture of peptides and reference modified peptides to obtain data relating to the peptides in the sample; and (d) comparing the data relating to the peptides in the sample with data in a database of modified peptides using a computer programme; wherein the database of modified peptides is compiled by a method comprising: (i) obtaining peptides from a sample; (ii) enriching modified peptides from the peptides obtained in step (i); (iii) carrying out liquid chromatography-tandem mass spectrometry (LC- MS/MS) on the enriched modified peptides obtained in step (ii); (iv) comparing the modified peptides detected in step (iii) to a known reference database in order to identify the modified peptides; and (v) compiling data relating to the modified peptides identified in step (iv) into a database.