A peptide immunoaffinity LC-MS/MS strategy for quantifying the GPCR protein, S1PR1 in human colon biopsies.

S1PR1, a G protein-coupled receptor (GPCR) protein, is a therapeutic target for treatment of autoimmune diseases. As a potential biomarker for drug effect and patient stratification, it is of great significance to measure it in biological samples. However, due to the hydrophobic nature of S1PR1 and the difficulties in extraction and solubilization, as well as low expression levels, quantitative determination of S1PR1 remains challenging. In this work, a peptide immunoaffinity LC-MS/MS method was developed to quantify S1PR1 in biopsy-sized colon samples with an LLOQ of 7.81 pM. Peptide immunoaffinity LC-MS/MS based strategy has achieved the desired sensitivity for low abundance S1PR1, and the same strategy could be applied to quantify S1PR1 in multiple species and other GPCR proteins.