International Journal of Molecular Sciences Review The Multifaceted Mas-Related G Protein-Coupled Receptor Member X2 in Allergic Diseases and Beyond Paola Leonor Quan 1,* , Marina Sabaté-Brescó 1,2,† , Yanru Guo 3,4, Margarita Martín 3,4,† and Gabriel Gastaminza 1,2,† 1 Department of Allergy and Clinical Immunology, Clínica Universidad de Navarra, 31008 Pamplona, Spain;
[email protected] (M.S.-B.);
[email protected] (G.G.) 2 Navarra Health Research Institute (Instituto de Investigación Sanitaria de Navarra) (IdiSNA), 31008 Navarra, Spain 3 Biochemistry Unit, Biomedicine Department, Faculty of Medicine, University of Barcelona, 08036 Barcelona, Spain;
[email protected] (Y.G.);
[email protected] (M.M.) 4 Laboratory of Clinical and Experimental Respiratory Immunoallergy, IDIBAPS, 08036 Barcelona, Spain * Correspondence:
[email protected] † Research Network: Research Network on Asthma, Drug Adverse Reactions and Allergy (Red de Investigación en Asma, Reacciones Adversas a Fármacos y Alergia) (ARADyAL), Spain. Abstract: Recent research on mast cell biology has turned its focus on MRGPRX2, a new member of the Mas-related G protein-coupled subfamily of receptors (Mrgprs), originally described in noci- ceptive neurons of the dorsal root ganglia. MRGPRX2, a member of this group, is present not only in neurons but also in mast cells (MCs), specifically, and potentially in other cells of the immune system, such as basophils and eosinophils. As emerging new functions for this receptor are studied, a variety of both natural and pharmacologic ligands are being uncovered, linked to the ability to induce Citation: Quan, P.L.; Sabaté-Brescó, receptor-mediated MC activation and degranulation. The diversity of these ligands, characterized in M.; Guo, Y.; Martín, M.; Gastaminza, their human, mice, or rat homologues, seems to match that of the receptor’s interactions.