Tetrahydrobiopterin from cyanide-degrading bacterium Bacillus pumilus strain SVD06 induces apoptosis in human lung adenocarcinoma cell (A549)

Tetrahydrobiopterin (BH4) is an essential biological cofactor and a derivative of pterin which is considered potent anticancer agents. In continuation of our previous study on the identification of BH4 from cyanide-degrading Bacillus pumilus, the present study focuses on evaluating the anticancer properties of BH4 on A549, a human lung adenocarcinoma. Anticancer activity analysis shows that BH4 inhibited A549 cell growth after 24 h of incubation with 0.02 mg/mL. In acridine orange/ethidium bromide staining, BH4-treated A549 cells showed apoptotic morphology. BH4 treatment caused cell cycle arrest at G0/G1 phase compared to control cells. BH4 augmented p53 expression in alveolar cancer cells by downregulating MDM2 levels. There was downregulation of casp-3 and upregulation of iNOS gene in BH4-treated A549 cells. Further, docking studies indicated that BH4 had significant interactions with the above proteins affirming the apoptosis mechanism. Thus, BH4 could be considered a potential anticancer drug.

Control of Biofilm Formation by an Agrobacterium tumefaciens Pterin-Binding Periplasmic Protein Conserved Among Pathogenic Bacteria

Biofilm formation and surface attachment in multiple Alphaproteobacteria is driven by unipolar polysaccharide (UPP) adhesins. The pathogen Agrobacterium tumefaciens produces a UPP adhesin, which is regulated by the intracellular second messenger cyclic diguanylate monophosphate (cdGMP). Prior studies revealed that DcpA, a diguanylate cyclase-phosphodiesterase (DGC-PDE), is crucial in control of UPP production and surface attachment. DcpA is regulated by PruR, a protein with distant similarity to enzymatic domains known to coordinate the molybdopterin cofactor (MoCo). Pterins are bicyclic nitrogen-rich compounds, several of which are formed via a non-essential branch of the folate biosynthesis pathway, distinct from MoCo. The pterin-binding protein PruR controls DcpA activity, fostering cdGMP breakdown and dampening its synthesis. Pterins are excreted and we report here that PruR associates with these metabolites in the periplasm, promoting interaction with the DcpA periplasmic domain. The pteridine reductase PruA, which reduces specific dihydro-pterin molecules to their tetrahydro forms, imparts control over DcpA activity through PruR. Tetrahydromonapterin preferentially associates with PruR relative to other related pterins, and the PruR-DcpA interaction is decreased in a pruA mutant. PruR and DcpA are encoded in an operon that is conserved amongst multiple Proteobacteria including mammalian pathogens. Crystal structures reveal that PruR and several orthologs adopt a conserved fold, with a pterin-specific binding cleft that coordinates the bicyclic pterin ring. These findings define a new pterin-responsive regulatory mechanism that controls biofilm formation and related cdGMP-dependent phenotypes in A. tumefaciens and is found in multiple additional bacterial pathogens.

Polyphenisms and polymorphisms: Genetic variation in plasticity and color variation within and among bluefin killifish populations

The presence of stable color polymorphisms within populations begs the question of how genetic variation is maintained. Consistent variation among populations in coloration, especially when correlated with environmental variation, raises questions about whether environmental conditions affect either the fulcrum of those balanced polymorphisms, the plastic expression of coloration, or both. Color patterns in male bluefin killifish provoke both types of questions. Red and yellow morphs are common in all populations. Blue males are more common in tannin-stained swamps relative to clear springs. Here, we combined crosses with a manipulation of light to explore how genetic variation and phenotypic plasticity shape these patterns. We found that the variation in coloration is attributable mainly to two axes of variation: (1) a red-yellow axis with yellow being dominant to red, and (2) a blue axis that can override red-yellow and is controlled by genetics, phenotypic plasticity, and genetic variation for phenotypic plasticity. The variation among populations in plasticity suggests it is adaptive in some populations but not others. The variation among sires in plasticity within the swamp population suggests balancing selection may be acting not only on the red-yellow polymorphism but also on plasticity for blue coloration.

Synthesis, Redox and Spectroscopic Properties of Pterin of Molybdenum Cofactors

Pterins are bicyclic heterocycles that are found widely across Nature and are involved in a variety of biological functions. Notably, pterins are found at the core of molybdenum cofactor (Moco) containing enzymes in the molybdopterin (MPT) ligand that coordinates molybdenum and facilitates cofactor activity. Pterins are diverse and can be widely functionalized to tune their properties. Herein, the general methods of synthesis, redox and spectroscopic properties of pterin are discussed to provide more insight into pterin chemistry and their importance to biological systems.

The integrative biology of pigment organelles, a quantum chemical approach

Coloration is a complex phenotypic trait involving both physical and chemical processes at a multiscale level, from molecules to tissues. Pigments, whose main property is to absorb specific wavelengths of visible light, are usually deposited in specialized organelles or complex matrices comprising proteins, metals, ions and redox compounds, among others. By modulating electronic properties and stability, interactions between pigments and these molecular actors can lead to color tuning. Furthermore, pigments are not only important for visual effects but also provide other critical functions, such as detoxification and antiradical activity. Hence, integrative studies of pigment organelles are required to understand how pigments interact with their cellular environment. In this review, we show how quantum chemistry, a computational method that models the molecular and optical properties of pigments, has provided key insights into the mechanisms by which pigment properties, from color to reactivity, are modulated by their organellar environment. These results allow to rationalize and to predict the way pigments behave in supramolecular complexes, up to the complete modelling of pigment organelles. We also discuss the main limitations of quantum chemistry, emphasizing the need for carrying experimental work with identical vigor. We finally suggest that taking into account the ecology of pigments (i.e. how they interact with these various other cellular components and at higher organizational levels) will lead to a greater understanding of how and why animals are vividly and variably colored, two fundamental questions in organismal biology.

Exploring the scope of DBU-promoted amidations of 7-methoxycarbonylpterin

The synthetic utility of pterins is often hampered by the notorious insolubility of this heterocycle, slowing the development of medicinally relevant pteridine derivatives. Reactions which expedite the development of new pterins are thus of great importance. Through a dual role of diazabicycloundecene (DBU), 7-carboxymethylpterin is converted to the soluble DBU salt, with additional DBU promoting an ester-to-amide transformation. We have explored this reaction to assess its scope and identify structural features in the amines which significantly affect success, monitored the reaction kinetics using a pseudo-first order kinetics model, and further adapted the reaction conditions to allow for product formation in as little as 5 min, with yields often >80%.

The contribution of nanostructures towards the wing patterning of yellow Catopsilia pomona. How it differs from the lime?

Polyphenism, an adaptation to survive throughout the year, is shown by many butterflies including Catopsilia pomona. With the variation of seasons, different morphs were found. Among all the morphs, lime exists throughout the year whereas the yellow one is available only in the winter season. The current study deciphers the colouration mechanism of yellow morph using various microscopic and spectroscopic techniques. The scanning electron microscopy analysis reveals various types of scales on the dorsal as well as the ventral side. The shape of the cover scale varies from region to region. The fine structural arrangement of the scale like window, ridge, microrib, crossrib and pigments vary throughout the wing. The pigment present in the wing is pterin as evidenced from the shape and its isolation technique. Absorption spectroscopy further confirms the presence of various types of pterin within the wing. Scanning electron microscopy discloses the dense amount of pigments within the wing. The fine structural arrangement of the wing of yellow C. pomona is compared with the yellow region of the lime C. pomona. All together, the current study describes the fine structural arrangement of the wing of yellow C. pomona and the various types of pterin which contribute towards the wing colouration. The advantage of yellow morph over lime is also discussed in this paper.

The thermophilic biomass-degrading bacterium Caldicellulosiruptor bescii utilizes two enzymes to oxidize glyceraldehyde 3-phosphate during glycolysis

Caldicellulosiruptor bescii is an extremely thermophilic, cellulolytic bacterium with a growth optimum at 78 °C and is the most thermophilic cellulose degrader known. It is an attractive target for biotechnological applications, but metabolic engineering will require an in-depth understanding of its primary pathways. A previous analysis of its genome uncovered evidence that C. bescii may have a completely uncharacterized aspect to its redox metabolism, involving a tungsten-containing oxidoreductase of unknown function. Herein, we purified and characterized this new member of the aldehyde ferredoxin oxidoreductase family of tungstoenzymes. We show that it is a heterodimeric glyceraldehyde-3-phosphate (GAP) ferredoxin oxidoreductase (GOR) present not only in all known Caldicellulosiruptor species, but also in 44 mostly anaerobic bacterial genera. GOR is phylogenetically distinct from the monomeric GAP-oxidizing enzyme found previously in several Archaea. We found that its large subunit (GOR-L) contains a single tungstopterin site and one iron-sulfur [4Fe-4S] cluster, that the small subunit (GOR-S) contains four [4Fe-4S] clusters, and that GOR uses ferredoxin as an electron acceptor. Deletion of either subunit resulted in a distinct growth phenotype on both C₅ and C₆ sugars, with an increased lag phase, but higher cell densities. Using metabolomics and kinetic analyses, we show that GOR functions in parallel with the conventional GAP dehydrogenase, providing an alternative ferredoxin-dependent glycolytic pathway. These two pathways likely facilitate the recycling of reduced redox carriers (NADH and ferredoxin) in response to environmental H₂ concentrations. This metabolic flexibility has important implications for the future engineering of this and related species.

Pterin-pigmented nanospheres create the colours of the polymorphic damselfly Ischnura elegans

Animal colours commonly act as signals for mates or predators. In many damselfly species, both sexes go through a developmental colour change as adults, and females often show colour polymorphism, which may have a function in mate choice, avoidance of mating harassment and camouflage. In the blue-tailed damselfly, Ischnura elegans, young males are bright green and turn blue as they reach maturity. Females are red ( rufescens) or violet ( violacea) as immatures and, when mature, either mimic the blue colour of the males ( androchrome), or acquire an inconspicuous olive-green ( infuscans) or olive-brown ( obsoleta). The genetic basis of these differences is still unknown. Here, we quantify the colour development of all morphs of I. elegans and investigate colour formation by combining anatomical data and reflectance spectra with optical finite-difference time-domain simulations. While the coloration primarily arises from a disordered assembly of nanospheres in the epidermis, morph-dependent changes result from adjustments in the composition of pterin pigments within the nanospheres, and from associated shifts in optical density. Other pigments fine-tune hue and brilliance by absorbing stray light. These mechanisms produce an impressive palette of colours and offer guidance for genetic studies on the evolution of colour polymorphism and visual communication.

Testing the potential mechanisms for the maintenance of a genetic color polymorphism in bluefin killifish populations

The maintenance of genetic variation in the face of natural selection is a long-standing question in evolutionary biology. In the bluefin killifish Lucania goodei, male coloration is polymorphic. Males can produce either red or yellow coloration in their anal fins, and both color morphs are present in all springs. These 2 morphs are heritable and how they are maintained in nature is unknown. Here, we tested 2 mechanisms for the maintenance of the red/yellow color morphs. Negative frequency-dependent mating success predicts that rare males have a mating advantage over common males. Spatial variation in fitness predicts that different color morphs have an advantage in different microhabitat types. Using a breeding experiment, we tested these hypotheses by creating populations with different ratios of red to yellow males (5 red:1 yellow; 1 red:5 yellow) and determining male mating success on shallow and deep spawning substrates. We found no evidence of negative frequency-dependent mating success. Common morphs tended to have higher mating success, and this was particularly so on shallow spawning substrates. However, on deep substrates, red males enjoyed higher mating success than yellow males, particularly so when red males were rare. However, yellow males did not have an advantage at either depth nor when rare. We suggest that preference for red males is expressed in deeper water, possibly due to alterations in the lighting environment. Finally, male pigment levels were correlated with one another and predicted male mating success. Hence, pigmentation plays an important role in male mating success.

Quantification of Live Bacterial Sensing for Chemotaxis and Phagocytosis and of Macropinocytosis

Initial immunological defense mechanisms to pathogen invasion rely on innate pathways of chemotaxis and phagocytosis, original to ancient phagocytes. Although chemotaxis has been well-studied in mammalian and model systems using purified chemoattractants in defined conditions, directed movement toward live bacteria has been more difficult to assess. Dictyostelium discoideum is a professional phagocyte that chemotaxes toward bacteria during growth-phase in a process to locate nutrient sources. Using Dictyostelium as a model, we have developed a system that is able to quantify chemotaxis to very high sensitivity. Here, Dictyostelium can detect various chemoattractants at concentrations <1 nM. Given this exceedingly sensitive signal response, Dictyostelium will migrate directionally toward live gram positive and gram negative bacteria, in a highly quantifiable manner, and dependent upon bacterially-secreted chemoattractants. Additionally, we have developed a real-time, quantitative assay for phagocytosis of live gram positive and gram negative bacteria. To extend the analyses of endocytic functions, we further modified the system to quantify cellular uptake via macropinocytosis of smaller (<100 kDa) molecules. These various approaches provide novel means to dissect potential for identification of novel chemoattractants and mechanistic factors that are essential for chemotaxis, phagocytosis, and/or macropinocytosis and for more detailed understanding in host-pathogen interactive defenses.

8-Mercaptoguanine Derivatives as Inhibitors of Dihydropteroate Synthase

Dihydropteroate synthase (DHPS) is an enzyme of the folate biosynthesis pathway, which catalyzes the formation of 7,8-dihydropteroate (DHPt) from 6-hydroxymethyl-7,8-dihydropterin pyrophosphate (DHPPP) and para-aminobenzoic acid (pABA). DHPS is the long-standing target of the sulfonamide class of antibiotics that compete with pABA. In the wake of sulfa drug resistance, targeting the structurally rigid (and more conserved) pterin site has been proposed as an alternate strategy to inhibit DHPS in wild-type and sulfa drug resistant strains. Following the work on developing pterin-site inhibitors of the adjacent enzyme 6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase (HPPK), we now present derivatives of 8-mercaptoguanine, a fragment that binds weakly within both enzymes, and quantify sub-μm binding using surface plasmon resonance (SPR) to Escherichia coli DHPS (EcDHPS). Eleven ligand-bound EcDHPS crystal structures delineate the structure-activity relationship observed providing a structural framework for the rational development of novel, substrate-envelope-compliant DHPS inhibitors.

The Agrobacterium tumefaciens CheY-like protein ClaR regulates biofilm formation

The switch from a motile, planktonic existence to an attached biofilm is a major bacterial lifestyle transition that is often mediated by complex regulatory pathways. In this report, we describe a CheY-like protein required for control of the motile-to-sessile switch in the plant pathogen Agrobacterium tumefaciens. This regulator, which we have designated ClaR, possesses two distinct CheY-like receiver (REC) domains and is involved in the negative regulation of biofilm formation, through production of the unipolar polysaccharide (UPP) adhesin and cellulose. The ClaR REC domains share predicted structural homology with characterized REC domains and contain the majority of active site residues known to be essential for protein phosphorylation. REC1 is missing the conserved aspartate (N72) residue and although present in REC 2 (D193), it is not required for ClaR-dependent regulation suggesting that phosphorylation, which modulates the activity of many CheY-like proteins, appears not to be essential for ClaR activity. We also show that ClaR-dependent negative regulation of attachment is diminished significantly in mutants for PruA and PruR, proteins known to be involved in a pterin-mediated attachment regulation pathway. In A. tumefaciens, pterins are required for control of the intracellular signal cyclic diguanylate monophosphate through the DcpA regulator, but our findings suggest that pterin-dependent ClaR control of attachment can function independently from DcpA, including dampening of c-di-GMP levels. This report of a novel CheY-type biofilm regulator in A. tumefaciens thus also adds significant details to the role of pterin-mediated signalling.

YedY: A Mononuclear Molybdenum Enzyme with a Redox-Active Ligand?

A recent electrochemical investigation suggests that the mononuclear molybdenum enzyme YdeY utilizes redox-active ligands during catalysis.

Unraveling the Degradation Mechanism of Purine Nucleotides Photosensitized by Pterins: The Role of Charge-Transfer Steps

Photosensitized reactions contribute to the development of skin cancer and are used in many applications. Photosensitizers can act through different mechanisms. It is currently accepted that if the photosensitizer generates singlet molecular oxygen ((1) O2 ) upon irradiation, the target molecule can undergo oxidation by this reactive oxygen species and the reaction needs dissolved O2 to proceed, therefore the reaction is classified as (1) O2 -mediated oxidation (type II mechanism). However, this assumption is not always correct, and as an example, a study on the degradation of 2'-deoxyguanosine 5'-monophosphate photosensitized by pterin is presented. A general mechanism is proposed to explain how the degradation of biological targets, such as nucleotides, photosensitized by pterins, naturally occurring (1) O2 photosensitizers, takes place through an electron-transfer-initiated process (type I mechanism), whereas the contribution of the (1) O2 -mediated oxidation is almost negligible.

Crystal structure of (2-amino-7-methyl-4-oxido-pteridine-6-carboxyl-ato-κ(3) O (4),N (5),O (6))aqua-(1,10-phenanthroline-κ(2) N,N')copper(II) trihydrate

In a hydrated copper(II) complex, 2-amino-7-methyl-4-oxidopteridine-6-carboxyl­ate and 1,10-phenanthroline ligands chelate the Cu^II cation while a water mol­ecule further coordinates to the Cu^II cation to complete the elongated distorted octa­hedral coordination geometry.

In the title compound, [Cu(C₈H₅N₅O₃)(C₁₂H₈N₂)(H₂O)]·3H₂O, the Cu^II cation is O,N,O′-chelated by the 2-amino-7-methyl-4-oxidopteridine-6-carboxyl­ate anion and N,N′-chelated by the 1,10-phenanthroline (phen) ligand. A water mol­ecule further coordinates to the Cu^II cation to complete the elongated distorted octa­hedral coordination geometry. In the mol­ecule, the pteridine ring system is essentially planar [maximum deviation = 0.055 (4) Å], and its mean plane is nearly perpendicular to the phen ring system [dihedral angle = 85.97 (3)°]. In the crystal, N—H⋯O, O—H⋯N and O—H⋯·O hydrogen bonds, as well as weak C—H⋯O hydrogen bonds and C—H⋯π inter­actions, link the complex mol­ecules and lattice water mol­ecules into a three-dimensional supra­molecular architecture. Extensive π–π stacking between nearly parallel aromatic rings of adjacent mol­ecules are also observed, the centroid-to-centroid distances being 3.352 (2), 3.546 (3), 3.706 (3) and 3.744 (3) Å.

Neopterin and biopterin as biomarkers of immune system activity associated with crating in broiler chickens

Neopterin and biopterin belong to a group of unconjugated pterin derivates. These biomolecules are present in many animal species and perform several functions. Pterin concentrations may provide additional information on the effect of stress on immune system activity. This study focused on an investigation of the effect of crating on plasma concentrations of neopterin and biopterin in broilers. The effects of 2 crating periods (2 and 4 h) were monitored in Hubbard broilers (n = 90) aged 42 d. After a given crating period, randomly selected chickens from each group were sampled immediately and the remaining chickens were sampled after 24 h. Plasma corticosterone increased (P < 0.001) immediately after 2 and 4 h crating, but no difference between the crated and the control noncrated broilers was found 24 h later. Immediately after crating, neopterin in 2- and 4-h broilers did not differ from the control, but 24 h later a decrease (P = 0.011) in plasma neopterin was found in 4-h broilers compared with the control. Simultaneously, 24 h after crating, neopterin levels in 2- and 4-h broilers decreased (P < 0.001) in comparison with the levels immediately after crating. Plasma biopterin was higher (P < 0.001) in 4-h broilers than in the control immediately after the crating. A time of sampling effect (P = 0.016) was found for the heterophil-to-lymphocyte ratio, with heterophil-to-lymphocyte ratio higher 24 h after crating in comparison with its level immediately after the crating. This study shows that crating may significantly affect the immune system of broiler chickens. This is corroborated by the increase in plasma biopterin concentrations in broilers immediately after crating and the decrease in plasma neopterin concentrations in broilers 24 h after crating. The correlations were found for widely used indicators of acute and chronic stress in birds [i.e., plasma corticosterone concentrations (biopterin) and the heterophil-to-lymphocyte ratio (neopterin), respectively].

Enhancing pterin and para-aminobenzoate content is not sufficient to successfully biofortify potato tubers and Arabidopsis thaliana plants with folate

Folates are important cofactors in one-carbon metabolism in all living organisms. Since only plants and micro- organisms are capable of biosynthesizing folates, humans depend entirely on their diet as a folate source. Given the low folate content of several staple crop products, folate deficiency affects regions all over the world. Folate biofortification of staple crops through enhancement of pterin and para-aminobenzoate levels, precursors of the folate biosynthesis pathway, was reported to be successful in tomato and rice. This study shows that the same strategy is not sufficient to enhance folate content in potato tubers and Arabidopsis thaliana plants and concludes that other steps in folate biosynthesis and/or metabolism need to be engineered to result in substantial folate accumulation. The findings provide a plausible explanation why, more than half a decade after the proof of concept in rice and tomato, successful folate biofortification of other food crops through enhancement of para-aminobenzoate and pterin content has not been reported thus far. A better understanding of the folate pathway is required in order to determine an engineering strategy that can be generalized to most staple crops.

7-Substituted pterins provide a new direction for ricin A chain inhibitors

Ricin is a potent toxin found in castor seeds. The A chain, RTA, enzymaticlly depurinates a specific adenosine in ribosomal RNA, inhibiting protein synthesis. Ricin is a known chemical weapons threat having no effective antidote. This makes the discovery of new inhibitors of great importance. We have previously used 6-substituted pterins, such as pteroic acid, as an inhibitor platform with moderate success. We now report the success of 7-carboxy pterin (7CP) as an RTA inhibitor; its binding has been monitored using both kinetic and temperature shift assays and by X-ray crystallography. We also discuss the synthesis of various derivatives of 7CP, and their binding affinity and inhibitory effects, as part of a program to make effective RTA inhibitors.

Pterin chemistry and its relationship to the molybdenum cofactor

The molybdenum cofactor is composed of a molybdenum coordinated by one or two rather complicated ligands known as either molybdopterin or pyranopterin. Pterin is one of a large family of bicyclic N-heterocycles called pteridines. Such molecules are widely found in Nature, having various forms to perform a variety of biological functions. This article describes the basic nomenclature of pterin, their biological roles, structure, chemical synthesis and redox reactivity. In addition, the biosynthesis of pterins and current models of the molybdenum cofactor are discussed.

Sensing UV/blue: pterin as a UV-A absorbing chromophore of cryptochrome

Cyanobacteria sense and respond to changes in an ambient light environment using highly specialized photoreceptors coupled to signal transduction pathways. Synechocystis sp. PCC 6803 is currently used as a model system to study light signal transduction in cyanobacteria. Recently, several important players, including photoreceptors and other signaling partners, have been identified in Synechocystis sp. PCC 6803. However, the nature of the molecules that act as UV/blue light sensors (and their downstream signaling mechanism) has not been elucidated. It has been postulated that pterins might serve as possible photoreceptor pigments for some behavioral responses induced by UV/blue light. By investigating the photomovement of wild-type and a pgtA mutant to UV/blue light, we demonstrated that cyanopterin is indeed involved in inhibiting negative phototaxis under UV/blue light. In this addendum, we provide additional evidence showing that the UV/blue action spectrum of the phototactic response coincides with the fluorescence spectrum of the in vivo cyanobacterial cryptochrome, DASH. Based on these results, we discuss the potential role of pterin as a UV-A absorbing chromophore of the cryptochrome in Synechocystis sp. PCC 6803.