Targeted Protein Quantification Using Parallel Reaction Monitoring (PRM).

Targeted proteomics represents an efficient method to quantify proteins of interest with high sensitivity and accuracy. Targeted approaches were first established for triple quadrupole instruments, but the emergence of hybrid instruments allowing for high-resolution and accurate-mass measurements of MS/MS fragment ions enabled the development of parallel reaction monitoring (PRM). In PRM analysis, specific peptides are measured as representatives of proteins in complex samples, with the full product ion spectra being acquired, allowing for identification and quantification of the peptides. Ideally, corresponding stable isotope-labeled peptides are spiked into the analyzed samples to account for technical variation and enhance the precision. Here, we describe the development of a PRM assay including the selection of appropriate peptides that fulfill the criteria to serve as unique surrogates of the targeted proteins. We depict the sequential steps of method development and the generation of calibration curves. Furthermore, we present the open-access tool CalibraCurve for the determination of the linear concentration ranges and limits of quantification (LOQ).