The G protein?coupled cysteinyl leukotriene receptor CysLT<
sub>
1<
/sub>
R mediates inflammatory processes and plays a major role in numerous disorders, including asthma, allergic rhinitis, cardiovascular disease, and cancer. Selective CysLT<
sub>
1<
/sub>
R antagonists are widely prescribed as antiasthmatic drugs
however, these drugs demonstrate low effectiveness in some patients and exhibit a variety of side effects. To gain deeper understanding into the functional mechanisms of CysLTRs, we determined the crystal structures of CysLT<
sub>
1<
/sub>
R bound to two chemically distinct antagonists, zafirlukast and pranlukast. The structures reveal unique ligand-binding modes and signaling mechanisms, including lateral ligand access to the orthosteric pocket between transmembrane helices TM4 and TM5, an atypical pattern of microswitches, and a distinct four-residue?coordinated sodium site. These results provide important insights and structural templates for rational discovery of safer and more effective drugs.