Cloning and characterization of luciferase from an Asian firefly Pygoluciola qingyu and its comparison with other beetle luciferases

The bioluminescence system of luminescent beetles has extensive applications in biological imaging, protein labeling and drug screening. To explore wild luciferases with excellent catalytic activity and thermal stability, we cloned the luciferase of Pygoluciola qingyu, one species living in areas of high temperature and with strong bioluminescence, by combining transcriptomic sequencing and reverse transcription polymerase chain reaction (RT-PCR). The total length of luciferase gene is 1638 bp and the luciferase consists 544 amino acids. The recombinant P. qingyu luciferase was produced in vitro and its characteristics were compared with those of eight luciferases from China firefly species and two commercial luciferases. Compared with these luciferases, the P. qingyu luciferase shows the highest luminescence activity at room temperature (about 25-28 ℃) with similar KM value for D-luciferin and ATP to the Photinus pyralis luciferase. The P. qingyu luciferase activity was highest at 35 ℃ and can keep high activity at 30-40 ℃, which suggests the potential of P. qingyu luciferase for in vivo and cell application. Our results provide new insights into P. qingyu luciferase and give a new resource for the application of luciferases.

Luciola mingrelica firefly luciferase as a marker in bioluminescent immunoassays

Chemical modification of the enzymes with biospecific macromolecules is used in various fields of biotechnology to impart new functions or improve their properties and is a fast and convenient way to get the final products. The preparation of highly active, stable, and functionally active conjugates of the thermostable luciferase through the NH2-groups or free SH-groups of the enzyme with target molecules of different molecular weight (albumin, avidin from chicken eggs, antibodies, and progesterone) is described. The obtained conjugates were successfully tested as a reporter in bioluminescent immunoassay for the detection of the molecules and pathogens. Thus, the luc-albumin (Luc-Alb) and luc-insulin (Luc-Ins) conjugates were used in competitive ELISA for the detection of an analyte (albumin or insulin) in the samples. Luc-progesterone (Luc-Pg) was used in the rapid homogeneous immunoassay of progesterone by the BRET technique with the detection limit of 0.5 ng/ml. Luciferase conjugates with avidin (Luc-Avi) and secondary and primary antibodies (Luc-RAM and Luc-Sal) were used for enzyme immunoassay detection of Salmonella paratyphi A cells with the cell detection limit of 5 × 104 CFU/ml. To reduce the detection limit of Salmonella cells, we developed a pseudo-homogeneous bioluminescent enzyme immunoassay of cells using a new matrix for the analyte capture-polystyrene microparticles coated with Pluronic F108, covalently labeled with Sal antibodies. This allowed to achieve efficient trapping of cells from solution, significantly reduced nonspecific sorption and decreased the cell detection limit to 2.7 × 103 CFU/ml without prior concentration of the sample. The methodology that was developed in this study can be applied for the development of novel bioanalytical systems based on firefly luciferases.

Molecular cloning, characterization, and evolution analysis of the luciferase genes from three sympatric sibling fireflies (Lampyridae: Lampyrinae, Diaphanes)

Firefly adult bioluminescence functions as signal communication between sexes. How sympatric sibling species with similar glow pattern recognize their conspecific mates remains largely unknown. To better understand the role of the luciferases of sympatric fireflies in recognizing mates, we cloned the luciferase genes of three sympatric forest dwelling fireflies (Diaphanes nubilus, Diaphanes pectinealis, and Diaphanes sp2) and evaluated their enzyme characteristics. Our data show that the amino acid (AA) sequences of all three luciferases are highly conserved, including the identities (D. nubilus vs D. pectinealis: 99%; D. nubilus vs Diaphanes sp2: 98.5%; D. pectinealis vs Diaphanes sp2: 99.4%) and the protein structures. Three recombinant luciferases produced in vitro all possess significant luminescence activity at pH 7.8, and similar maximum emission spectrum (D. nubilus: 562 nm; D. pectinealis and Diaphanes sp2: 564 nm). They show the highest activity at 10 °C (D. pectinealis, Diaphanes sp2) and 15 °C (D. nubilus), and completely inactivation at 45 °C. Their K_M for D-luciferin and ATP were 2.7 μM and 92 μM (D. nubilus), 3.7 μM and 49 μM (D. pectinealis), 3.5 μM and 46 μM (Diaphanes sp2). Phylogenetic analyses support that D. nubilus is sister to D. pectinealis with Diaphanes sp2 at their base, which further cluster with Pyrocoelia. All combined data indicate that sympatric Diaphanes species have similar luciferase characteristics, suggesting that other strategies (e.g., pheromone, active time, etc.) may be adopted to recognize mates. Our data provide new insights into Diaphanes luciferases and their evolution.

Point mutations in firefly luciferase C-domain demonstrate its significance in green color of bioluminescence

Firefly luciferase is a two-domain enzyme that catalyzes the bioluminescent reaction of firefly luciferin oxidation. Color of the emitted light depends on the structure of the enzyme, yet the exact color-tuning mechanism remains unknown by now, and the role of the C-domain in it is rarely discussed, because a very few color-shifting mutations in the C-domain were described. Recently we reported a strong red-shifting mutation E457K in the C-domain; the bioluminescence spectra of this enzyme were independent of temperature or pH. In the present study we investigated the role of the residue E457 in the enzyme using the Luciola mingrelica luciferase with a thermostabilized N-domain as a parent enzyme for site-directed mutagenesis. We obtained a set of mutants and studied their catalytic properties, thermal stability and bioluminescence spectra. Experimental spectra were represented as a sum of two components (bioluminescence spectra of putative "red" and "green" emitters); λmax of these components were constant for all the mutants, but the ratio of these emitters was defined by temperature and mutations in the C-domain. We suggest that each emitter is stabilized by a specific conformation of the active site; thus, enzymes with two forms of the active site coexist in the reactive media. The rigid structure of the C-domain is crucial for maintaining the conformation corresponding to the "green" emitter. We presume that the emitters are the keto- and enol forms of oxyluciferin.

Approaches to engineer stability of beetle luciferases

Luciferase enzymes from fireflies and other beetles have many important applications in molecular biology, biotechnology, analytical chemistry and several other areas. Many novel beetle luciferases with promising properties have been reported in the recent years. However, actual and potential applications of wild-type beetle luciferases are often limited by insufficient stability or decrease in activity of the enzyme at the conditions of a particular assay. Various examples of genetic engineering of the enhanced beetle luciferases have been reported that successfully solve or alleviate many of these limitations. This mini-review summarizes the recent advances in development of mutant luciferases with improved stability and activity characteristics. It discusses the common limitations of wild-type luciferases in different applications and presents the efficient approaches that can be used to address these problems.

Thermostabilization of firefly luciferase by in vivo directed evolution

Firefly luciferase is widely used in a number of areas of biotechnology and molecular biology. However, rapid inactivation of wild-type (WT) luciferases at elevated temperatures often hampers their application. A simple non-lethal in vivo screening scheme was used to identify thermostable mutants of luciferase in Escherichia coli colonies. This scheme allowed carrying out each cycle of mutagenesis in a rapid and efficient manner. Four rounds of directed evolution were conducted on a part of the gene coding for amino acid residues 130-390 of Luciola mingrelica luciferase. The resultant mutant designated 4TS had a half-life of 10 h at 42°C, which is 65-fold higher compared with the WT luciferase. Moreover, the mutant 4TS showed a 1.9-fold increase in specific activity, 5.7-fold reduction of K(m) for ATP and a higher-temperature optimum compared with the WT enzyme. 4TS contains eight mutations, four of which are suggested to be mainly responsible for the enhancement of thermostability: R211L, A217V, E356K and S364C. Thus, directed evolution with non-lethal colony screening for in vivo bioluminescence activity proved to be an effective and efficient approach for increasing thermal stability of luciferase while retaining high catalytic activity.