International Journal of Molecular Sciences Article Bioluminescent Properties of Semi-Synthetic Obelin and Aequorin Activated by Coelenterazine Analogues with Modifications of C-2, C-6, and C-8 Substituents 1, 2,3, 1 2, Elena V. Eremeeva y , Tianyu Jiang y , Natalia P. Malikova , Minyong Li * and Eugene S. Vysotski 1,* 1 Photobiology Laboratory, Institute of Biophysics SB RAS, Federal Research Center “Krasnoyarsk Science Center SB RAS”, Krasnoyarsk 660036, Russia;
[email protected] (E.V.E.);
[email protected] (N.P.M.) 2 Key Laboratory of Chemical Biology (MOE), Department of Medicinal Chemistry, School of Pharmaceutical Sciences, Shandong University, Jinan 250012, China;
[email protected] 3 State Key Laboratory of Microbial Technology, Shandong University–Helmholtz Institute of Biotechnology, Shandong University, Qingdao 266237, China * Correspondence:
[email protected] (M.L.);
[email protected] (E.S.V.); Tel.: +86-531-8838-2076 (M.L.); +7-(391)-249-44-30 (E.S.V.); Fax: +86-531-8838-2076 (M.L.); +7-(391)-290-54-90 (E.S.V.) These authors contributed equally to this work. y Received: 23 June 2020; Accepted: 27 July 2020; Published: 30 July 2020 Abstract: Ca2+-regulated photoproteins responsible for bioluminescence of a variety of marine organisms are single-chain globular proteins within the inner cavity of which the oxygenated coelenterazine, 2-hydroperoxycoelenterazine, is tightly bound. Alongside with native coelenterazine, photoproteins can also use its synthetic analogues as substrates to produce flash-type bioluminescence. However, information on the effect of modifications of various groups of coelenterazine and amino acid environment of the protein active site on the bioluminescent properties of the corresponding semi-synthetic photoproteins is fragmentary and often controversial.