Over time, organisms have evolved strategies to cope with the abundance of dioxygen on Earth. Oxygen-utilizing enzymes tightly control the reactions involving O2 mostly by modulating the reactivity ...of their cofactors. Flavins are extremely versatile cofactors that are capable of undergoing redox reactions by accepting either one electron or two electrons, alternating between the oxidized and the reduced states. The physical and chemical principles of flavin-based chemistry have been investigated widely. In the following pages we summarize the state of the art on a key area of research in flavin enzymology: the molecular basis for the activation of O2 by flavin-dependent oxidases and monooxygenases. In general terms, oxidases use O2 as an electron acceptor to produce H2O2, while monooxygenases activate O2 by forming a flavin intermediate and insert an oxygen atom into the substrate. First, we analyze how O2 reaches the flavin cofactor embedded in the protein matrix through dedicated access pathways. Then we approach O2 activation from the perspective of the monooxygenases, their preferred intermediate, the C(4a)–(hydro)peroxyflavin, and the cases in which other intermediates have been described. Finally, we focus on understanding how the architectures developed in the active sites of oxidases promote O2 activation and which other factors operate in its reactivity.
Regio- and stereoselective Baeyer–Villiger oxidations are difficult to achieve by classical chemical means, particularly when large, functionalized molecules are to be converted. Biocatalysis using ...flavin-containing Baeyer–Villiger monooxygenases (BVMOs) is a well-established tool to address these challenges, but known BVMOs have shortcomings in either stability or substrate selectivity. We characterized a novel BVMO from the thermophilic fungus Thermothelomyces thermophila, determined its three-dimensional structure, and demonstrated its use as a promising biocatalyst. This fungal enzyme displays excellent enantioselectivity, acts on various ketones, and is particularly active on polycyclic molecules. Most notably we observed that the enzyme can perform oxidations on both the A and D ring when converting steroids. These functional properties can be linked to unique structural features, which identify enzymes acting on bulky substrates as a distinct subgroup of the BVMO class.
Cyclohexanone monooxygenase (CHMO) is a promising biocatalyst for industrial reactions owing to its broad substrate spectrum and excellent regio‐, chemo‐, and enantioselectivity. However, the low ...stability of many Baeyer–Villiger monooxygenases is an obstacle for their exploitation in industry. Characterization and crystal structure determination of a robust CHMO from Thermocrispum municipale is reported. The enzyme efficiently converts a variety of aliphatic, aromatic, and cyclic ketones, as well as prochiral sulfides. A compact substrate‐binding cavity explains its preference for small rather than bulky substrates. Small‐scale conversions with either purified enzyme or whole cells demonstrated the remarkable properties of this newly discovered CHMO. The exceptional solvent tolerance and thermostability make the enzyme very attractive for biotechnology.
Looking like a true survivor: The discovery of a robust cyclohexanone monooxygenase (CHMO) that shows great promise as an oxidative biocatalyst is reported. This enzyme (TmCHMO) efficiently converts a variety of aliphatic, aromatic, and cyclic ketones, as well as prochiral sulfides, and was found to be much more thermostable and solvent tolerant than known CHMOs.
A recent study associates carbon with single photon emitters (SPEs) in hexagonal boron nitride (h-BN). This observation, together with the high mobility of carbon in h-BN, suggests the existence of ...SPEs based on carbon clusters. Here, by means of density functional theory calculations, we studied clusters of substitutional carbon atoms up to tetramers in h-BN. Two different conformations of neutral carbon trimers have zero-point line energies and shifts of the phonon sideband compatible with typical photoluminescence spectra. Moreover, some conformations of two small C clusters next to each other result in photoluminescence spectra similar to those found in the experiments. We also showed that vacancies are unable to reproduce the typical features of the phonon sideband observed in most measurements because of the large spectral weight of low-energy breathing modes, ubiquitous in such defects.
Red Lapacho (
Tabebuia impetiginosa, syn.
Tabebuia avellanedae), a canopy tree indigenous to the Amazonian rainforest and other parts of South America, has been acclaimed to be one of the ...“miraculous” cures for cancer and tumours. For the first time, during the 1960s, it attracted considerable attention in Brazil and Argentina as a ‘wonder drug’. Traditionally, the botanical drug is widely used in local and traditional phytomedicine, usually ingested as a decoction prepared from the inner bark of the tree to treat numerous conditions like bacterial and fungal infections, fever, syphilis, malaria, trypanosomiasis, as well as stomach and bladder disorders.
As early as 1873, biomedical uses of Red Lapacho (“Pau D’Arco”) were reported. In 1967 after reports in the Brazilian press it came back to the light of clinicians (and the public in general). The news magazine
O’Cruzeiro started reporting “miraculous” cures in cancer patients in a hospital. Natural sciences interest in the plant also began in the 1960s when the United States National Cancer Institute (NCI) systematically began researching plant extracts all over the world looking for active compounds against cancer and looked at
Tabebuia impetiginosa in considerable detail.
Two main bioactive components have been isolated from
Tabebuia impetiginosa: lapachol and β-lapachone. β-Lapachone is considered to be the main anti-tumour compound, and pro-apoptotic effects were observed
in vitro. Some mechanistic studies on this compound's molecular effects have been conducted. The other main constituents isolated from Red Lapacho are also reviewed briefly.
The drug appears to be generally safe and one of the most important interactions of
Tabebuia impetiginosa has been associated with interference in the biological cycle of Vitamin K in the body.
The botanical (drug) material available on the international markets seems to be of varying quality and composition, making a specific assessment of the products’ therapeutic claims problematic. This also highlights the need for appropriate analytical techniques, which are reviewed as well.
The bioscientific evidence for products derived from
Tabebuia impetiginosa is insufficient and one of the core challenges of future research will be – based on the recognition of the drug's widespread use – to establish appropriate quality control procedures. Further research into the clinical effects and the pharmacology of chemically characterized extracts is also warranted.
Enzyme instability is an important limitation for the investigation and application of enzymes. Therefore, methods to rapidly and effectively improve enzyme stability are highly appealing. In this ...study we applied a computational method (FRESCO) to guide the engineering of an alcohol dehydrogenase. Of the 177 selected mutations, 25 mutations brought about a significant increase in apparent melting temperature (Δ
≥ +3 °C). By combining mutations, a 10-fold mutant was generated with a
of 94 °C (+51 °C relative to wild type), almost reaching water's boiling point, and the highest increase with FRESCO to date. The 10-fold mutant's structure was elucidated, which enabled the identification of an activity-impairing mutation. After reverting this mutation, the enzyme showed no loss in activity compared to wild type, while displaying a
of 88 °C (+45 °C relative to wild type). This work demonstrates the value of enzyme stabilization through computational library design.
Altered interplay between gut mucosa and microbiota during treated HIV infection may possibly contribute to increased bacterial translocation and chronic immune activation, both of which are ...predictors of morbidity and mortality. Although a dysbiotic gut microbiota has recently been reported in HIV+ individuals, the metagenome gene pool associated with HIV infection remains unknown. The aim of this study is to characterize the functional gene content of gut microbiota in HIV+ patients and to define the metabolic pathways of this bacterial community, which is potentially associated with immune dysfunction. We determined systemic markers of innate and adaptive immunity in a cohort of HIV-infected individuals on successful antiretroviral therapy without comorbidities and in healthy non-HIV-infected subjects. Metagenome sequencing revealed an altered functional profile, with enrichment of the genes involved in various pathogenic processes, lipopolysaccharide biosynthesis, bacterial translocation, and other inflammatory pathways. In contrast, we observed depletion of genes involved in amino acid metabolism and energy processes. Bayesian networks showed significant interactions between the bacterial community, their altered metabolic pathways, and systemic markers of immune dysfunction. This study reveals altered metabolic activity of microbiota and provides novel insight into the potential host-microbiota interactions driving the sustained inflammatory state in successfully treated HIV-infected patients.
Continuum emission, also called white-light emission (WLE), and permanent changes of the magnetic field (ΔBLOS) are often observed during solar flares. However, their relation and precise mechanisms ...are still unknown. We study statistically the relationship between ΔBLOS and WLE during 75 solar flares of different strengths and locations on the solar disk. We analyze SDO/HMI data and determine for each pixel in each flare if it exhibited WLE and/or ΔBLOS. We then investigate the occurrence, strength, and spatial size of the WLE, its dependence on flare energy, and its correlation to the occurrence of ΔBLOS. We detected WLE in 44/75 flares and ΔBLOS in 59/75 flares. We find that WLE and ΔBLOS are related, and their locations often overlap between 0% and 60%. Not all locations coincide, thus potentially indicating differences in their origin. We find that the WL area is related to the flare class by a power law, and extend the findings of previous studies, that the WLE is related to the flare class by a power law, to also be valid for C-class flares. To compare unresolved (Sun-as-a-star) WL measurements with our data, we derive a method to calculate temperatures and areas of such data under the blackbody assumption. The calculated unresolved WLE areas improve, but still differ to the resolved flaring area by about a factor of 5-10 (previously 10-20), which could be explained by various physical or instrumental causes. This method could also be applied to stellar flares to determine their temperatures and areas independently.
This article explores the role of risk perception in adaptation to stress through comparative case studies of coffee farmers’ responses to climatic and non-climatic stressors. We hypothesized that ...farmers associating these changes with high risk would be more likely to make adaptations than those who saw the events as part of normal variation. Nevertheless, we found that farmers who associated events with high risk were not more likely to engage in specific adaptations. Adaptive responses were more clearly associated with access to land than perception of risk, suggesting that adaptation is more a function of exogenous constraints on decision making than perception.
Traditionally, the strongest magnetic fields on the Sun have been measured in sunspot umbrae. More recently, however, much stronger fields have been measured at the ends of penumbral filaments ...carrying the Evershed and counter-Evershed flows. Superstrong fields have also been reported within a light bridge separating two umbrae of opposite polarities. We aim to accurately determine the strengths of the strongest fields in a light bridge using an advanced inversion technique and to investigate their detailed structure. We analyze observations from the spectropolarimeter on board the Hinode spacecraft of the active region AR 11967. The thermodynamic and magnetic configurations are obtained by inverting the Stokes profiles using an inversion scheme that allows multiple height nodes. Both the traditional 1D inversion technique and the so-called 2D coupled inversions, which take into account the point-spread function of the Hinode telescope, are used. We find a compact structure with an area of 32.7 arcsec2 within a bipolar light bridge with field strengths exceeding 5 kG, confirming the strong fields in this light bridge reported in the literature. Two regions associated with downflows of ∼5 km s−1 harbor field strengths larger than 6.5 kG, covering a total area of 2.97 arcsec2. The maximum field strength found is 8.2 kG, which is the largest ever observed field in a bipolar light bridge up to now.
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