7o3u
The crystal structure of obelin from Obelia longissima bound with v-coelenterazine
Structural highlights
FunctionOBL_OBELO Ca(2+)-dependent bioluminescence photoprotein. Displays an emission peak at 470 nm (blue light). Trace amounts of calcium ion trigger the intramolecular oxidation of the chromophore, coelenterazine into coelenteramide and CO(2) with the concomitant emission of light. Publication Abstract from PubMedCoelenterazine-v (CTZ-v), a synthetic derivative with an additional benzyl ring, yields a bright bioluminescence of Renilla luciferase and its "yellow" mutant with a significant shift in the emission spectrum toward longer wavelengths, which makes it the substrate of choice for deep tissue imaging. Although Ca(2+) -regulated photoproteins activated with CTZ-v also display red-shifted light emission, in contrast to Renilla luciferase their bioluminescence activities are very low, which makes photoproteins activated by CTZ-v unusable for calcium imaging. Here, we report the crystal structure of Ca(2+) -regulated photoprotein obelin with 2-hydroperoxycoelenterazine-v (obelin-v) at 1.80 A resolution. The structures of obelin-v and obelin bound with native CTZ revealed almost no difference; only the minor rearrangement in hydrogen-bond pattern and slightly increased distances between key active site residues and some atoms of 2-hydroperoxycoelenterazine-v were found. The fluorescence quantum yield (PhiFL ) of obelin bound with coelenteramide-v (0.24) turned out to be even higher than that of obelin with native coelenteramide (0.19). Since both obelins are in effect the enzyme-substrate complexes containing the 2-hydroperoxy adduct of CTZ-v or CTZ, we reasonably assume the chemical reaction mechanisms and the yields of the reaction products (PhiR ) to be similar for both obelins. Based on these findings we suggest that low bioluminescence activity of obelin-v is caused by the low efficiency of generating an electronic excited state (PhiS ). In turn, the low PhiS value as compared to that of native CTZ might be the result of small changes in the substrate microenvironment in the obelin-v active site. Crystal structure of semisynthetic obelin-v.,Larionova MD, Wu L, Eremeeva EV, Natashin PV, Gulnov DV, Nemtseva EV, Liu D, Liu ZJ, Vysotski ES Protein Sci. 2022 Feb;31(2):454-469. doi: 10.1002/pro.4244. Epub 2021 Nov 29. PMID:34802167[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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