Effects of alcohols on fluorescence intensity and color of a discharged-obelin-based biomarker

Water-Soluble Polymer Polyethylene Glycol: Effect on the Bioluminescent Reaction of the Marine Coelenterate Obelia and Coelenteramide-Containing Fluorescent Protein

The current paper considers the effects of a water-soluble polymer (polyethylene glycol (PEG)) on the bioluminescent reaction of the photoprotein obelin from the marine coelenterate Obelia longissima and the product of this bioluminescent reaction: a coelenteramide-containing fluorescent protein (CCFP). We varied PEG concentrations (0–1.44 mg/mL) and molecular weights (1000, 8000, and 35,000 a.u.). The presence of PEG significantly increased the bioluminescent intensity of obelin but decreased the photoluminescence intensity of CCFP; the effects did not depend on the PEG concentration or the molecular weight. The photoluminescence spectra of CCFP did not change, while the bioluminescence spectra changed in the course of the bioluminescent reaction. The changes can be explained by different rigidity of the media in the polymer solutions affecting the stability of the photoprotein complex and the efficiency of the proton transfer in the bioluminescent reaction. The results predict and explain the change in the luminescence intensity and color of the marine coelenterates in the presence of water-soluble polymers. The CCFP appeared to be a proper tool for the toxicity monitoring of water-soluble polymers (e.g., PEGs).

Enzymatic Responses to Low-Intensity Radiation of Tritium

The present study considers a possible role of enzymatic reactions in the adaptive response of cells to the beta-emitting radionuclide tritium under conditions of low-dose exposures. Effects of tritiated water (HTO) on the reactions of bacterial luciferase and NAD(P)H:FMN-oxidoreductase, as well as a coupled system of these two reactions, were studied at radioactivity concentrations ≤ 200 MBq/L. Additionally, one of the simplest enzymatic reactions, photobiochemical proton transfer in Coelenteramide-containing Fluorescent Protein (CLM-FP), was also investigated. We found that HTO increased the activity of NAD(P)H:FMN-oxidoreductase at the initial stage of its reaction (by up to 230%); however, a rise of luciferase activity was moderate (<20%). The CLM-FP samples did not show any increase in the rate of the photobiochemical proton transfer under the exposure to HTO. The responses of the enzyme systems were compared to the 'hormetic' response of luminous marine bacterial cells studied earlier. We conclude that (1) the oxidoreductase reaction contributes significantly to the activation of the coupled enzyme system and bacterial cells by tritium, and (2) an increase in the organization level of biological systems promotes the hormesis phenomenon.

Loss of FZO1 gene results in changes of cell dynamics in fission yeast

Mitochondrial fission and fusion dynamics are critical cellular processes, and abnormalities in these processes are associated with severe human disorders, such as Beckwith-Wiedemann syndrome, neurodegenerative diseases, Charcot-Marie-Tooth disease type 6, multiple symmetric lipomatosis and microcephaly. Fuzzy onions protein 1 (Fzo1p) regulates mitochondrial outer membrane fusion. In the present study, Schizosaccharomyces pombe (S. pombe) was used to explore the effect of FZO1 gene deletion on cell dynamics in mitosis. The mitochondrial morphology results showed that the mitochondria appeared to be fragmented and tubular in wild-type cells; however, they were observed to accumulate in fzo1Δ cells. The FZO1 gene deletion was demonstrated to result in slow proliferation, sporogenesis defects, increased microtubule (MT) number and actin contraction defects in S. pombe. The FZO1 gene deletion also affected the rate of spindle elongation and phase time at the metaphase and anaphase, as well as spindle MT organization. Live-cell imaging was performed on mutant strains to observe three distinct kinetochore behaviors (normal, lagging and mis-segregation), as well as abnormal spindle breakage. The FZO1 gene deletion resulted in coenzyme and intermediate metabolite abnormalities as determined via metabolomics analysis. It was concluded that the loss of FZO1 gene resulted in deficiencies in mitochondrial dynamics, which may result in deficiencies in spindle maintenance, chromosome segregation, spindle breakage, actin contraction, and coenzyme and intermediate metabolite levels.

Monitoring of Low-Intensity Exposures via Luminescent Bioassays of Different Complexity: Cells, Enzyme Reactions, and Fluorescent Proteins

The current paper reviews the applications of luminescence bioassays for monitoring the results of low-intensity exposures which produce a stimulative effect. The impacts of radioactivity of different types (alpha, beta, and gamma) and bioactive compounds (humic substances and fullerenols) are under consideration. Bioassays based on luminous marine bacteria, their enzymes, and fluorescent coelenteramide-containing proteins were used to compare the results of the low-intensity exposures at the cellular, biochemical, and physicochemical levels, respectively. High rates of luminescence response can provide (1) a proper number of experimental results under comparable conditions and, therefore, proper statistical processing, with this being highly important for "noisy" low-intensity exposures; and (2) non-genetic, i.e., biochemical and physicochemical mechanisms of cellular response for short-term exposures. The results of cellular exposures were discussed in terms of the hormesis concept, which implies low-dose stimulation and high-dose inhibition of physiological functions. Dependencies of the luminescence response on the exposure time or intensity (radionuclide concentration/gamma radiation dose rate, concentration of the bioactive compounds) were analyzed and compared for bioassays of different organization levels.

Tuning the fluorescence of calcium-discharged photoprotein obelin via mutating at the His22-Phe88-Trp92 triad - a QM/MM study

The fluorescence (FL) of calcium-discharged photoprotein (CaDP) can be altered by easily mutating CaDP without modifying coelenteramide (CLM), which is the decarboxylation product of coelenterazine in calcium-regulated photoprotein. The His22-Phe88-Trp92 triad (the ordering numbers of three amino acids are sorted by a crystal structure (PDB: 2F8P) of calcium-discharged obelin, i.e., CaDP-obelin) is closely related to CaDP-obelin FL, since it exists in close proximity to the 5-p-hydroxyphenyl of CLM. Therefore, it is important to thoroughly investigate how the mutations of this triad affect the emission color of CaDP-obelin FL. In this study, by mutating wild-type CaDP-obelin (WT) at the His22-Phe88-Trp92 triad, we theoretically constructed its nine mutants of separable FL colors. Through combined quantum mechanics and molecular mechanics (QM/MM) calculations and molecular dynamics (MD) simulations, the influence of the mutations of this triad on the CaDP-obelin FL was analyzed considering the H-bond effect and the charge effect. This study demonstrated that the mutations at the His22-Phe88-Trp92 triad redistribute the charges on the D-π-A molecule, CLM, change the charge transfer from the D to the (π + A) moiety, and thereby alter the FL emission. Appending more negative charges on the phenolate moiety of CLM benefits the FL redshift.

Protein-based fluorescent bioassay for low-dose gamma radiation exposures

The study suggests an application of a coelenteramide-containing fluorescent protein (CLM-CFP) as a simplest bioassay for gamma radiation exposures. "Discharged obelin," a product of the bioluminescence reaction of the marine coelenterate Obelia longissima, was used as a representative of the CLM-CFP group. The bioassay is based on a simple enzymatic reaction-photochemical proton transfer in the coelenteramide-apoprotein complex. Components of this reaction differ in fluorescence color, providing, by this, an evaluation of the proton transfer efficiency in the photochemical process. This efficiency depends on the microenvironment of the coelenteramide within the protein complex, and, hence, can evaluate a destructive ability of gamma radiation. The CLM-CFP samples were exposed to gamma radiation (¹³⁷Cs, 2 mGy/h) for 7 and 16 days at 20 °C and 5 °C, respectively. As a result, two fluorescence characteristics (overall fluorescence intensity and contributions of color components to the fluorescence spectra) were identified as bioassay parameters. Both parameters demonstrated high sensitivity of the CLM-CFP-based bioassay to the low-dose gamma radiation exposure (up to 100 mGy). Higher temperature (20 °C) enhanced the response of CLM-CFP to gamma radiation. This new bioassay can provide fluorescent multicolor assessment of protein destruction in cells and physiological liquids under exposure to low doses of gamma radiation. Graphical abstract ᅟ.

Fluorescent coelenteramide-containing protein as a color bioindicator for low-dose radiation effects

The study addresses the application of fluorescent coelenteramide-containing proteins as color bioindicators for radiotoxicity evaluation. Biological effects of chronic low-dose radiation are under investigation. Tritiated water (200 MBq/L) was used as a model source of low-intensive ionizing radiation of beta type. 'Discharged obelin,' product of bioluminescent reaction of marine coelenterate Obelia longissimi, was used as a representative of the coelenteramide-containing proteins. Coelenteramide, fluorophore of discharged obelin, is a photochemically active molecule; it produces fluorescence forms of different color. Contributions of 'violet' and 'blue-green' forms to the visible fluorescence serve as tested parameters. The contributions depend on the coelenteramide's microenvironment in the protein, and, hence, evaluate distractive ability and toxicity of radiation. The protein samples were exposed to beta radiation for 18 days, and maximal dose accumulated by the samples was 0.28 Gy, being close to a tentative limit of a low-dose interval. Increase of relative contribution of 'violet' fluorescence under exposure to the beta irradiation was revealed. High sensitivity of the protein-based test system to low-dose ionizing radiation (to 0.03 Gy) was demonstrated. The study develops physicochemical understanding of radiotoxic effects. Graphical abstract Coelenteramide-containing protein (discharged obelin) changes fluorescence color under exposure to low-dose ionizing radiation of tritium.

Variability of fluorescence spectra of coelenteramide-containing proteins as a basis for toxicity monitoring

Nowadays, physicochemical approach to understanding toxic effects remains underdeveloped. A proper development of such mode would be concerned with simplest bioassay systems. Coelenteramide-Containing Fluorescent Proteins (CLM-CFPs) can serve as proper tools for study primary physicochemical processes in organisms under external exposures. CLM-CFPs are products of bioluminescent reactions of marine coelenterates. As opposed to Green Fluorescent Proteins, the CLM-CFPs are not widely applied in biomedical research, and their potential as colored biomarkers is undervalued now. Coelenteramide, fluorophore of CLM-CFPs, is a photochemically active molecule; it acts as a proton donor in its electron-excited states, generating several forms of different fluorescent state energy and, hence, different fluorescence color, from violet to green. Contributions of the forms to the visible fluorescence depend on the coelenteramide microenvironment in proteins. Hence, CLM-CFPs can serve as fluorescence biomarkers with color differentiation to monitor results of destructive biomolecule exposures. The paper reviews experimental and theoretical studies of spectral-luminescent and photochemical properties of CLM-CFPs, as well as their variation under different exposures - chemicals, temperature, and ionizing radiation. Application of CLM-CFPs as toxicity bioassays of a new type is justified.

Immunochemical Micro Imaging Analyses for the Detection of Proteins in Artworks

The present review is aimed at reporting on the most advanced and recent applications of immunochemical imaging techniques for the localization of proteins within complex and multilayered paint stratigraphies. Indeed, a paint sample is usually constituted by the superimposition of different layers whose characterization is fundamental in the evaluation of the state of conservation and for addressing proper restoration interventions. Immunochemical methods, which are based on the high selectivity of antigen-antibody reactions, were proposed some years ago in the field of cultural heritage. In addition to enzyme-linked immunosorbent assays for protein identification, immunochemical imaging methods have also been explored in the last decades, thanks to the possibility to localize the target analytes, thus increasing the amount of information obtained and thereby reducing the number of samples and/or analyses needed for a comprehensive characterization of the sample. In this review, chemiluminescent, spectroscopic and electrochemical imaging detection methods are discussed to illustrate potentialities and limits of advanced immunochemical imaging systems for the analysis of paint cross-sections.

Ultraviolet fluorescence of coelenteramide and coelenteramide-containing fluorescent proteins. Experimental and theoretical study

Coelenteramide-containing fluorescent proteins are products of bioluminescent reactions of marine coelenterates. They are called 'discharged photoproteins'. Their light-induced fluorescence spectra are variable, depending considerably on external conditions. Current work studies a dependence of light-induced fluorescence spectra of discharged photoproteins obelin, aequorin, and clytin on excitation energy. It was demonstrated that photoexcitation to the upper electron-excited states (260-300nm) of the discharged photoproteins initiates a fluorescence peak in the near UV region, in addition to the blue-green emission. To characterize the UV fluorescence, the light-induced fluorescence spectra of coelenteramide (CLM), fluorophore of the discharged photoproteins, were studied in methanol solution. Similar to photoproteins, the CLM spectra depended on photoexcitation energy; the additional peak (330nm) in the near UV region was observed in CLM fluorescence at higher excitation energy (260-300nm). Quantum chemical calculations by time depending method with B3LYP/cc-pVDZ showed that the conjugated pyrazine-phenolic fragment and benzene moiety of CLM molecule are responsible for the additional UV fluorescence peak. Quantum yields of CLM fluorescence in methanol were 0.028±0.005 at 270-340nm photoexcitation. A conclusion was made that the UV emission of CLM might contribute to the UV fluorescence of the discharged photoproteins. The study develops knowledge on internal energy transfer in biological structures - complexes of proteins with low-weight aromatic molecules.