Single-step purification of recombinant Gaussia luciferase from serum-containing culture medium of mammalian cells

A Comprehensive Exploration of Bioluminescence Systems, Mechanisms, and Advanced Assays for Versatile Applications

Bioluminescence has been a fascinating natural phenomenon of light emission from living creatures. It happens when the enzyme luciferase facilitates the oxidation of luciferin, resulting in the creation of an excited-state species that emits light. Although there are many bioluminescent systems, few have been identified. D-luciferin-dependent systems, coelenterazine-dependent systems, Cypridina luciferin-based systems, tetrapyrrole-based luciferins, bacterial bioluminescent systems, and fungal bioluminescent systems are natural bioluminescent systems. Since different bioluminescence systems, such as various combinations of luciferin-luciferase pair reactions, have different light emission wavelengths, they benefit industrial applications such as drug discovery, protein-protein interactions, in vivo imaging in small animals, and controlling neurons. Due to the expression of luciferase and easy permeation of luciferin into most cells and tissues, bioluminescence assays are applied nowadays with modern technologies in most cell and tissue types. It is a versatile technique in a variety of biomedical research. Furthermore, there are some investigated blue-sky research projects, such as bioluminescent plants and lamps. This review article is mainly based on the theory of diverse bioluminescence systems and their past, present, and future applications.

Reverse mutants of the catalytic 19 kDa mutant protein (nanoKAZ/nanoLuc) from Oplophorus luciferase with coelenterazine as preferred substrate

Native Oplophorus luciferase (OpLase) and its catalytic 19 kDa protein (wild KAZ) show highest luminescence activity with coelenterazine (CTZ) among CTZ analogs. Mutated wild KAZ with 16 amino acid substitutions (nanoKAZ/nanoLuc) utilizes bis-coelenterazine (bis-CTZ) as the preferred substrate and exhibits over 10-fold higher maximum intensity than CTZ. To understand the substrate selectivity of nanoKAZ between CTZ and bis-CTZ, we prepared the reverse mutants of nanoKAZ by amino acid replacements with the original amino acid residue of wild KAZ. The reverse mutant with L18Q and V27L substitutions (QL-nanoKAZ) exhibited 2.6-fold higher maximum intensity with CTZ than that of nanoKAZ with bis-CTZ. The catalytic properties of QL-nanoKAZ including substrate specificity, luminescence spectrum, luminescence kinetics, luminescence products of CTZ, and luminescence inhibition by deaza-CTZ analogs were characterized and were compared with other CTZ-utilizing luciferases such as Gaussia and Renilla luciferases. Thus, QL-nanoKAZ with CTZ could be used as a potential reporter protein for various luminescence assay systems. Furthermore, the crystal structure of QL-nanoKAZ was determined at 1.70 Å resolution. The reverse mutation at the L18Q and V27L positions of α2-helix in nanoKAZ led to changes in the local structures of the α4-helix and the β6- and β7-sheets, and might enhance its binding affinity and oxidation efficiency with CTZ to emit light.

Enzymatic conversion of dehydrocoelenterazine to coelenterazine using FMN-bound flavin reductase of NAD(P)H:FMN oxidoreductase

Coelenterazine (CTZ) is known as luciferin (a substrate) for the luminescence reaction with luciferase (an enzyme) in marine organisms and is unstable in aqueous solutions. The dehydrogenated form of CTZ (dehydrocoelenterazine, dCTZ) is stable and thought to be a storage form of CTZ and a recycling intermediate from the condensation reaction of coelenteramine and 4-hydroxyphenylpyruvic acid to CTZ. In this study, the enzymatic conversion of dCTZ to CTZ was successfully achieved using NAD(P)H:FMN oxidoreductase from the bioluminescent bacterium Vibrio fischeri ATCC 7744 (FRase) in the presence of NADH (the FRase-NADH reaction). CTZ reduced from dCTZ in the FRase-NADH reaction was identified by HPLC and LC/ESI-TOF-MS analyses. Thus, dCTZ can be enzymatically converted to CTZ in vitro. Furthermore, the concentration of dCTZ could be determined by the luminescence activity using the CTZ-utilizing luciferases (Gaussia luciferase or Renilla luciferase) coupled with the FRase-NADH reaction.

[Novel Technology for Studying Insulin Secretion: Imaging and Quantitative Analysis by a Bioluminescence Method]

We developed a method of video-rate bioluminescence imaging to visualize proteins secreted from living cells. A protein of interest was fused to Gaussia luciferase (GLase), and the luminescence signals of secreted GLase with coelenterazine (luciferin) were visualized at a video-rate of 30-500 ms/frame by using a water-cooled EM-CCD camera. We established a subclonal rat INS-1E cell line, named iGL cells, stably expressing the fusion protein of insulin and GLase (Insulin-GLase). By stimulation with high glucose, 3D-cultured iGL cells showed synchronized oscillatory secretion of insulin for over 1 h, as similarly observed in an isolated rat pancreatic islet. In 2D-cultured iGL cells, the luminescence images indicated that synchronized insulin secretion was localized in intercellular spaces between cells. Further, the relative amount of insulin secretion from iGL cells was easily determined with a luminometer, and we demonstrated that cell-cell interaction of beta cells is fundamental to increase glucose-stimulated insulin secretion by synchronization. Thus, iGL cells would be valuable for studying oscillatory insulin secretion and evaluating anti-diabetic drugs. Our bioluminescence imaging method with GLase could be generally used for investigating protein secretion in 2D and 3D cell culture systems.

Video-Rate Bioluminescence Imaging of Degranulation of Mast Cells Attached to the Extracellular Matrix

Degranulation refers to the secretion of inflammatory mediators, such as histamine, serotonin, and proteases, that are stored within the granules of mast cells and that trigger allergic reactions. The amount of these released mediators has been measured biochemically using cell mass. To investigate degranulation in living single cells, fluorescence microscopy has traditionally been used to observe the disappearance of granules and the appearance of these discharged granules within the plasma membrane by membrane fusion and the movement of granules inside the cells. Here, we developed a method of video-rate bioluminescence imaging to directly detect degranulation from a single mast cell by measuring luminescence activity derived from the enzymatic reaction between Gaussia luciferase (GLase) and its substrate coelenterazine. The neuropeptide Y (NPY), which was reported to colocalize with serotonin in the secretory granules, fused to GLase (NPY-GLase) was efficiently expressed in rat basophilic leukemia (RBL-2H3) cells, a mast-cell line, using a preferred human codon-optimized gene. Bioluminescence imaging analysis of RBL-2H3 cells expressing NPY-GLase and adhered on a glass-bottomed dish showed that the luminescence signals from the resting cells were negligible, while the luminescence signals of the secreted NPY-GLase were repeatedly detected after the addition of an antigen. In addition, this imaging method was applicable for observing degranulation in RBL-2H3 cells that adhered to the extracellular matrix (ECM). These results indicated that video-rate bioluminescence imaging using GLase will be a useful tool for detecting degranulation in single mast cells adhered to a variety of ECM proteins.

Bioluminescent and structural features of native folded Gaussia luciferase

The secreted luciferases responsible for light emission of marine copepods have gained popularity for being used in noninvasive imaging of intracellular events. The secreted luciferase of copepod Gaussia princeps is a one-subunit protein catalyzing coelenterazine oxidation to emit blue light. It consists of the N-terminal variable part that bears a signal peptide for secretion and the C-terminal catalytic domain containing ten highly conserved Cys residues supposing the existence of up to five SS bonds. Despite wide application of Gaussia luciferase in biomedical research, its biochemical properties are still insufficiently studied due to the general problem of obtaining the proper folded Cys-rich proteins in bacterial cells. Here we report the properties of the proper folded Gaussia luciferase produced in insect cells using baculovirus expression system. This high purity luciferase reveals the highest activity at 15-20 °C but retains only ~20% activity at 37 °C that may hamper its application for in vivo assays. The maximum of bioluminescent activity of GpLuc is found at NaCl concentrations in the range of 1.0-1.5 M and, furthermore, a high NaCl concentration enhances luciferase stability to thermal denaturation, i.e. Gaussia luciferase displays the features characteristic of halophilic enzymes. The studies on bioluminescence kinetics at different coelenterazine concentrations obviously show a positive cooperativity of Gaussia luciferase with coelenterazine (Hill coefficient - 1.8 ± 0.2; K_0.5-2.14 ± 0.17 μM). We suggest this effect to be rather due to the so-called kinetic cooperativity conditioned by conformational changes in response to substrate binding than to the presence of two catalytic sites.