Mapping histamine H4 receptor–ligand binding modes

The increasing number of G protein-coupled receptor (GPCR) crystal structures offers new opportunities for histamine receptor homology modeling. However, computational prediction of ligand binding modes in GPCRs such as the histamine H4 receptor (H4R), a receptor that plays an important role in inflammation, remains a challenging task. In the current work we have combined complementary in silico receptor modeling approaches with in vitro ligand structure–activity relationship (SAR) and protein site-directed mutagenesis studies to elucidate the binding modes of different ligand classes in H4R. By systematically considering different H4R modelling templates, ligand binding poses, and ligand protonation states in combination with docking and MD simulations we are able to explain ligand-specific mutation effects and subtle differences in ligand SAR. Our studies confirm that a combined theoretical and experimental approach represents a powerful strategy to map ligand–protein interactions.