MRM Assays Developed for 73 Human Plasma Proteins

One of our goals is to develop a rapid, sensitive, and specific method for detection and quantitation of proteins. The result of which is the development of MRM based assays for proteins in plasma. To see a list of proteins for which such assays have been successfully developed, please click here.

The MRM Approach

Sensitive and accurate quantitation of proteins by mass spectrometry is conducted by measuring the concentrations of proteolytic peptides as molecular surrogates of their corresponding intact proteins. The use of stable isotopes in quantitative proteomics workflows has had a great impact in improving the quality and reproducibility of MS-based protein quantitation. Untargeted MS-based quantitation workflows rely on exhaustive sample pre-fractionation methods, such as multidimensional chromatography which can be performed at both the protein and peptide levels. These techniques have the goal of detecting changes in the expression levels of as many proteins as possible, in an unbiased manner, over a wide dynamic range. These workflows are needed for the “discovery” phase, but are often too expensive in terms of time and reagent costs to be used in the subsequent “verification” or “validation” steps of a biomarker project, or in the ultimate clinical assay, where a large number of samples must be analyzed. Multiple reaction monitoring (MRM) is a tandem MS (MS/MS) technique unique to triple quadrupole MS instrumentation that is capable of rapid, sensitive, and specific quantitation of targeted analytes in highly-complex samples. As a targeted method MRM requires knowledge of the molecular weight of an analyte and its fragmentation behavior under collision-induced dissociation (CID) conditions. By combining careful choice of peptides and selection of MRM precursor and fragment ion pairs with the use of stable isotope-labeled standard (SIS) peptides, MRM can be used to determine, highly specifically and reproducibly, the absolute concentrations of peptides. The concentrations of the peptides can be used to infer the concentrations of the proteins the peptides came from.