Immunoassays with direct mass spectrometric detection

A rapid, specific, and sensitive method for the detection of protein-protein interactions is of crucial importance for drug discovery and clinical diagnostics. Mass spectrometry plays a major role in the analysis of proteins, but its application to the routine analysis of protein complexes has been lagging behind. A new strategy for high-throughput analysis of protein interactions is presented here. We demonstrate application to immunochemical questions such as epitope mapping, kinetic studies, and sandwich assays. The methodology is based on a direct mass spectrometric readout for antigen-antibody complexes in the 150-400 kDa range. This has become possible using a novel detector technology and chemical cross-linking to stabilize complexes for analysis by MALDI MS. We demonstrate high detection sensitivity ( femtomole quantities of antigen), high specificity ( specific detection of antigen directly in serum), high accuracy, and high speed ( minutes per assay), surpassing conventional analytical methods by more than 2 orders of magnitude.