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Coelenterazine-v (CTZ-v), a synthetic vinylene-bridged π-extended derivative, is able to significantly alter bioluminescence spectra of different CTZ-dependent luciferases and photoproteins by shifting them towards longer wavelengths. However, Ca2+-regulated photoproteins activated with CTZ-v display very low bioluminescence activities that hampers its usage as a substrate of photoprotein bioluminescence. Here, we report the crystal structure of semi-synthetic Ca2+-discharged obelin-v bound with the reaction product determined at 2.1 Å resolution. Comparison of the crystal structure of Ca2+-discharged obelin-v with those of other obelins before and after bioluminescence reaction reveals no considerable changes in the overall structure. However, the drastic changes in CTZ-binding cavity are observed owing to the completely different reaction product, coelenteramine-v (CTM-v). Since CTM-v is certainly the main product of obelin-v bioluminescence and is considered to be a product of the “dark” pathway of dioxetanone intermediate decomposition, it explains the low bioluminescence activity of obelin and apparently of other photoproteins with CTZ-v.

Cysteinyl leukotriene G protein-coupled receptors CysLT1 and CysLT2 regulate pro-inflammatory responses associated with allergic disorders. While selective inhibition of CysLT1R has been used for treating asthma and associated diseases for over two decades, CysLT2R has recently started to emerge as a potential drug target against atopic asthma, brain injury and central nervous system disorders, as well as several types of cancer. Here, we describe four crystal structures of CysLT2R in complex with three dual CysLT1R/CysLT2R antagonists. The reported structures together with the results of comprehensive mutagenesis and computer modeling studies shed light on molecular determinants of CysLTR ligand selectivity and specific effects of disease-related single nucleotide variants., Cysteinyl leukotriene G protein-coupled receptors CysLT1 and CysLT2 regulate pro-inflammatory responses associated with allergic disorders. Here, authors describe four crystal structures of CysLT2R in complex with three dual CysLT1R/CysLT2R antagonists, which shed light on CysLTR ligand selectivity.