ABSTRACT
The recombinant coelenterazine-dependent luciferases (isoforms MLuc164 and MLuc39) from the marine copepod Metridia longa were expressed as inclusion bodies in E. coli cells, dissolved in 6 M guanidinium chloride and folded in conditions developed for proteins containing intramolecular disulfide bonds. One of them (MLuc39) was obtained in an active monomeric form with a high yield. The luciferase bioluminescence is found to be initiated not only by free coelenterazine, but also by Ca2+-dependent coelenterazine-binding protein (CBP) of Renilla muelleri on Ca2+ addition. The use of CBP as a "substrate" provides higher light emission and simultaneously the lower level of background. The high purity MLuc39 can be detected down to attomol with a linear range extending over 5 orders of magnitude. The MLuc39 reveals also a high stability towards heating and chemical modification; the chemically synthesized biotinylated derivatives of the luciferase preserve 35-40% of the initial activity. The luciferase applicability as an in vitro bioluminescent reporter is demonstrated in model tandem bioluminescent solid-phase microassay combining the Ca2+-regulated photoprotein obelin and the Metridia luciferase.
Subject(s)
Copepoda/enzymology , Gene Expression , Luciferases/metabolism , Protein Folding , Amino Acid Sequence , Animals , Copepoda/genetics , Isoenzymes/chemistry , Isoenzymes/genetics , Isoenzymes/metabolism , Kinetics , Luciferases/chemistry , Luciferases/genetics , Molecular Sequence Data , Recombinant Proteins/chemistry , Recombinant Proteins/genetics , Recombinant Proteins/metabolism , Sequence Alignment , Spectrometry, FluorescenceABSTRACT
Two kinds of Ca(2+)-regulated photoprotein obelin with altered color of bioluminescence were obtained by active-center amino acid substitution. The mutant W92F-H22E emits violet light (lambda(max) = 390 nm) and the mutant Y139F emits greenish light (lambda(max) = 498 nm), with small spectral overlap, both display high activity and stability and thus may be used as reporters. For demonstration, the mutants were applied in dual-color simultaneous immunoassay of two gonadotropic hormones-follicle-stimulating hormone and luteinizing hormone. Bioluminescence of the reporters was simultaneously triggered by single injection of Ca(2+) solution, divided using band-pass optical filters and measured with a two-channel photometer. The sensitivity of simultaneous bioluminescence assay was close to that of a separate radioimmunoassay.
