Histamine Receptor H4 (HRH4)

Histamine receptors are G protein-coupled receptors (GPCRs) that have distinct tissue expression profiles and functional attributes. They have varying sensitivities to an array of agonist and antagonist molecules that are used in pharmacologic studies and in treating different medical conditions. HRH4 is almost 40% identical to HRH3. It contains an asp residue in transmembrane domain-1 (TM1), a DRY motif in TM2, a disulfide bond between the first and third extracellular loops, a trp in TM4 and TM6, a pro in TM5 and TM6, an NPxxY motif in TM7, and a potential palmitoylation site in the C-terminal tail. Northern blot analysis revealed expression of a 4.5-kb transcript restricted to peripheral blood leukocytes. RT-PCR analysis detected expression in thymus, small intestine, spleen, and colon.