GPCR proteomics:: Mass spectrometric and functional analysis of histamine H1 receptor after baculovirus-driven and in vitro cell free expression

The human histamine H-1 Receptor (hH(1)R) belongs to the family of G-protein coupled receptors (GPCRs), an attractive and proven class of drug targets in a wide range of therapeutic areas. However, due to the low amount of available purified protein and the hydrophobic nature of GPCRs, limited structural information is available on ligand-receptor interaction especially for the transmembrane (TM) domain regions where the majority of ligand-receptor interactions occur. During the last decades, proteomic techniques have increasingly become an important tool to reveal detailed information on the individual GPCR class, including post-translational modifications and characterizations of GPCRs binding pocket. Herein, we report the successful functional production and mass spectrometric characterization of the hH(1)R, after baculovirus-driven and in vitro cell-free expression. Using only MALDI-ToF, sequence coverage of more than 80%, including five hydrophobic TM domains was achieved. Moreover, we have identified an asparagine residue in the hH(1)R protein that is subject to N-linked glycosylation. This information would be valuable for drug discovery efforts by allowing us to further study H,R-ligand interactions using histaminergic ligands that covalently bind the hH(1)R, and eventually revealing binding sites of hH(1)R and other GPCRs.