The dark and bright sides of an enzyme: a three dimensional structure of the N-terminal domain of Zophobas morio luciferase-like enzyme, inferences on the biological function and origin of oxygenase/luciferase activity

Selective inhibition of Zophobas morio (Coleoptera: Tenebrionidae) luciferase-like enzyme luminescence by diclofenac and potential suitability for light-off biosensing

The accumulation of toxic carboxylic compounds may cause severe effects on the environment and living organisms. A luciferase-like enzyme, previously cloned from the Malpighian tubules of the non-luminescent Zophobas morio mealworm, displays thioesterification activity with a wide range of carboxylic substrates, and produces weak red luminescence in the presence of ATP and firefly d-luciferin, a xenobiotic for this organism. To better investigate the function of this enzyme in carboxylic xenobiotic detoxification, we analyzed the inhibitory effect of different xenobiotic carboxylic acids on the luminescence activity of this enzyme, including environmental pollutants and pharmaceutical compounds. Noteworthy, the anti-inflammatory drug diclofenac severely inhibited this luciferase-like enzyme luminescence activity, both in in vitro (IC₅₀ 20 μM) and in vivo in bacterial cells assays, when compared with other beetle luciferases. Similar results were obtained with its brighter I327S mutant. Kinetic analysis of diclofenac's effect on luminescence activity indicated mixed-type inhibition for both ATP and d-luciferin. Modelling studies showed five potential binding sites for diclofenac, including the coenzyme A binding site, which showed one of the highest binding constant. Taken together, these results raise the possibility of using this luciferase-like enzyme for the development of novel whole-cell luminescent biosensors for diclofenac and similar drugs.

Phrixotrix luciferase and 6'-aminoluciferins reveal a larger luciferin phenolate binding site and provide novel far-red combinations for bioimaging purposes

How the unique luciferase of Phrixothrix hirtus (PxRE) railroad worm catalyzes the emission of red bioluminescence using the same luciferin of fireflies, remains a mystery. Although PxRE luciferase is a very attractive tool for bioanalysis and bioimaging in hemoglobin rich tissues, it displays lower quantum yield (15%) when compared to green emitting luciferases (>40%). To identify which parts of PxRE luciferin binding site (LBS) determine bioluminescence color, and to develop brighter and more red-shifted emitting luciferases, we compared the effects of site-directed mutagenesis and of larger 6′-substituted aminoluciferin analogues (6′-morpholino- and 6′-pyrrolidinyl-LH) on the bioluminescence properties of PxRE and green-yellow emitting beetle luciferases. The effects of mutations in the benzothiazolyl and thiazolyl parts of PxRE LBS on the K_M and catalytic efficiencies, indicated their importance for luciferin binding and catalysis. However, the absence of effects on the bioluminescence spectrum indicated a less interactive LBS in PxRE during light emission. Mutations at the bottom of LBS of PxRE blue-shifted the spectra and increased catalytic efficiency, suggesting that lack of interactions of this part of LBS with excited oxyluciferin phenolate underlie red light emission. The much higher bioluminescence activity and red-shifted spectra of PxRE luciferase with 6′-morpholino- (634 nm) and 6′-pyrrolidinyl-luciferins (644 nm), when compared to other beetle luciferases, revealed a larger luciferin phenolate binding pocket. The size and orientation of the side-chains of L/I/H348 are critical for amino-analogues accommodation and modulate bioluminescence color, affecting the interactions and mobility of excited oxyluciferin phenolate. The PxRE luciferase and 6′-aminoluciferins provide potential far-red combinations for bioimaging applications.

Comparison of the Malpighian tubules and fat body transcriptional profiles of Zophobas morio larvae (Coleoptera: Tenebrionidae)

The Malpighian tubules in insects play an essential role in osmoregulation, through the transport of ions during excretion, whereas the fat body is usually associated with the intermediary metabolism. The tubules also are involved in excretion of organic solutes and xenobiotics. However, with the exception of a preliminary transcriptional survey of the Zophobas morio (Tenebrionidae) larval tubules, there are no detailed transcriptional analysis of this organ in Coleoptera. A luciferase-like enzyme that displays weak luminescence activity in the presence of firefly D-luciferin and ATP was cloned from the tubules of Z. morio larvae. In order to better understand the molecular physiology of Malpighian tubules and fat body in Coleoptera larvae, and to investigate the occurrence and functions of AMP-CoA ligases in these tissues, we performed a comparative transcriptional analysis of these tissues using Z. morio giant-mealworms. As expected, the tubules displayed organic and inorganic transporters, xenobiotic metabolism enzymes, V-ATPases, channels, and pumps. The fat body showed proteins that are synthesized in this tissue and secreted to the hemolymph, as well as enzymes involved in lipid and carbohydrate metabolism. These tissues are also involved in common pathways, such as nitrogen metabolism to degradation/excretion, eye pigments biosynthesis, immunity, and detoxification. The presence of coumarate-CoA ligase-like enzymes in these tissues suggest their involvement in the degradation of coumaric acid derivatives obtained from the diet, or alternatively, in the biosynthesis of compounds structurally related to coumaric acids such as eye pigments. Our results confirm to the physiological versatility of tubules and fat body in larval Coleoptera.