Formation of a complex containing ATP, Mg2+, and spermine. Structural evidence and biological significance

The influencers' era: how the environment shapes chromatin in 3D

Environment-epigenome interactions are emerging as contributors to disease risk and health outcomes. In fact, organisms outside of the laboratory are constantly exposed to environmental changes that can influence chromatin regulation at multiple levels, potentially impacting on genome function. In this review, we will summarize recent findings on how major external cues impact on 3D chromatin organization in different experimental systems. We will describe environment-induced 3D genome alterations ranging from chromatin accessibility to the spatial distribution of the genome and discuss their role in regulating gene expression.

Modulation of Ion Transport Across Plant Membranes by Polyamines: Understanding Specific Modes of Action Under Stress

This work critically discusses the direct and indirect effects of natural polyamines and their catabolites such as reactive oxygen species and γ-aminobutyric acid on the activity of key plant ion-transporting proteins such as plasma membrane H+ and Ca2+ ATPases and K+-selective and cation channels in the plasma membrane and tonoplast, in the context of their involvement in stress responses. Docking analysis predicts a distinct binding for putrescine and longer polyamines within the pore of the vacuolar TPC1/SV channel, one of the key determinants of the cell ionic homeostasis and signaling under stress conditions, and an additional site for spermine, which overlaps with the cytosolic regulatory Ca2+-binding site. Several unresolved problems are summarized, including the correct estimates of the subcellular levels of polyamines and their catabolites, their unexplored effects on nucleotide-gated and glutamate receptor channels of cell membranes and Ca2+-permeable and K+-selective channels in the membranes of plant mitochondria and chloroplasts, and pleiotropic mechanisms of polyamines' action on H+ and Ca2+ pumps.

Metal cation responsive anionic microgels: behaviour towards biologically relevant divalent and trivalent ions

Anionic poly(vinylcaprolactam-co-itaconicacid-co-dimethylitaconate) microgels were synthesized via dispersion polymerization and their responsiveness towards cations, namely Mg²⁺, Sr²⁺, Cu²⁺ and Fe³⁺, was investigated. The itaconic moieties chelate the metal ions which act as a crosslinker and decrease the electrostatic repulsion within the network, leading to a decrease in the gel size. The responsiveness towards the metal ion concentration has been studied via dynamic light scattering (DLS) and the number of ions bonded within the network has been quantified with ion chromatography. Through the protonation of the carboxylate groups in the gel network, their interaction with the cations is significantly lowered, and the metals are consequently released back in solution. The number of ions released was assessed also via ion chromatography for all four ions, whilst Mg²⁺ was also used as a model ion to display the reversibility of the system. The microgels can bond and release divalent cations over multiple cycles without undergoing any loss of functionality. Moreover, these gels also selectively entrap Fe³⁺ with respect to the remaining divalent cations, opening the possibility of using the proposed gels in the digestive tract as biocompatible chelating agents to fight iron overaccumulation.

Lipid kinases PIP5K7 and PIP5K9 are required for polyamine-triggered K+ efflux in Arabidopsis roots

Polyamines, such as putrescine, spermidine and spermine (Spm), are low-molecular-weight polycationic molecules present in all living organisms. Despite their implication in plant cellular processes, little is known about their molecular mode of action. Here, we demonstrate that polyamines trigger a rapid increase in the regulatory membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP₂ ), and that this increase is required for polyamine effects on K⁺ efflux in Arabidopsis roots. Using in vivo ³² P_i -labelling of Arabidopsis seedlings, low physiological (μm) concentrations of Spm were found to promote a rapid PIP₂ increase in roots that was time- and dose-dependent. Confocal imaging of a genetically encoded PIP₂ biosensor revealed that this increase was triggered at the plasma membrane. Differential ³² P_i -labelling suggested that the increase in PIP₂ was generated through activation of phosphatidylinositol 4-phosphate 5-kinase (PIP5K) activity rather than inhibition of a phospholipase C or PIP₂ 5-phosphatase activity. Systematic analysis of transfer DNA insertion mutants identified PIP5K7 and PIP5K9 as the main candidates involved in the Spm-induced PIP₂ response. Using non-invasive microelectrode ion flux estimation, we discovered that the Spm-triggered K⁺ efflux response was strongly reduced in pip5k7 pip5k9 seedlings. Together, our results provide biochemical and genetic evidence for a physiological role of PIP₂ in polyamine-mediated signalling controlling K⁺ flux in plants.

VOC fingerprints: metabolomic signatures of biothreat agents with and without antibiotic resistance

Category A and B biothreat agents are deemed to be of great concern by the US Centers for Disease Control and Prevention (CDC) and include the bacteria Francisella tularensis, Yersinia pestis, Burkholderia mallei, and Brucella species. Underscored by the impact of the 2020 SARS-CoV-2 outbreak, 2016 Zika pandemic, 2014 Ebola outbreak, 2001 anthrax letter attacks, and 1984 Rajneeshee Salmonella attacks, the threat of future epidemics/pandemics and/or terrorist/criminal use of pathogenic organisms warrants continued exploration and development of both classic and alternative methods of detecting biothreat agents. Volatile organic compounds (VOCs) comprise a large and highly diverse group of carbon-based molecules, generally related by their volatility at ambient temperature. Recently, the diagnostic potential of VOCs has been realized, as correlations between the microbial VOC metabolome and specific bacterial pathogens have been identified. Herein, we describe the use of microbial VOC profiles as fingerprints for the identification of biothreat-relevant microbes, and for differentiating between a kanamycin susceptible and resistant strain. Additionally, we demonstrate microbial VOC profiling using a rapid-throughput VOC metabolomics method we refer to as ‘simultaneous multifiber headspace solid-phase microextraction’ (simulti-hSPME). Finally, through VOC analysis, we illustrate a rapid non-invasive approach to the diagnosis of BALB/c mice infected with either F. tularensis SCHU S4 or Y. pestis CO92.

The functional role of polyamines in eukaryotic cells

Polyamines, consisting of putrescine, spermidine and spermine are essential for normal cell growth and viability in eukaryotic cells. Since polyamines are cations, they interact with DNA, ATP, phospholipids, specific kinds of proteins, and especially with RNA. Consequently, the functions of these acidic compounds and some proteins are modified by polyamines. In this review, the functional modifications of these molecules by polyamines are presented. Structural change of specific mRNAs by polyamines causes the stimulation of the synthesis of several different proteins, which are important for cell growth and viability. eIF5 A, the only known protein containing a spermidine derivative, i.e. hypusine, also functions at the level of translation. Experimental results thus far obtained strongly suggest that the most important function of polyamines is at the level of translation.

Methionine is required for cAMP-PKA-mediated morphogenesis and virulence of Candida albicans

Candida albicans is a major human fungal pathogen, causing superficial, as well as life-threatening invasive infections. Therefore, it has to adequately sense and respond to the host defense by expressing appropriate virulence attributes. The most important virulence factor of C. albicans is the yeast-to-hyphae morphogenetic switch, which can be induced by numerous environmental cues, including the amino acid methionine. Here, we show an essential role for methionine permease Mup1 in methionine-induced morphogenesis, biofilm formation, survival inside macrophages and virulence. Furthermore, we demonstrate that this process requires conversion of methionine into S-adenosyl methionine (SAM) and its decarboxylation by Spe2. The resulting amino-propyl group is then used for biosynthesis of polyamines, which have been shown to activate adenylate cyclase. Inhibition of the SPE2 SAM decarboxylase gene strongly impairs methionine-induced morphogenesis on specific media and significantly delays virulence in the mouse systemic infection model system. Further proof of the connection between methionine uptake and initial metabolism and the cAMP-PKA pathway was obtained by showing that both Mup1 and Spe2 are required for cAMP production in response to methionine. Our results suggest that amino acid transport and further metabolism are interesting therapeutic targets as inhibitors of this may prevent the morphogenetic switch, thereby preventing virulence.

Saccharomyces boulardii CNCM I-745 Improves Intestinal Enzyme Function: A Trophic Effects Review

Several properties of the probiotic medicinal yeast Saccharomyces boulardii CNCM I-745 contribute to its efficacy to prevent or treat diarrhoea. Besides immunologic effects, pathogen-binding and anti-toxin effects, as well as positive effects on the microbiota, S boulardii CNCM I-745 also has pronounced effects on digestive enzymes of the brush border membrane, known as trophic effects. The latter are the focus of this review. Literature has been reviewed after searching Medline and PMC databases. All relevant non-clinical and clinical studies are summarized. S. boulardii CNCM I-745 synthesizes and secretes polyamines, which have a role in cell proliferation and differentiation. The administration of polyamines or S. boulardii CNCM I-745 enhances the expression of intestinal digestive enzymes as well as nutrient uptake transporters. The signalling mechanisms leading to enzyme activation are not fully understood. However, polyamines have direct nucleic acid–binding capacity with regulatory impact. S. boulardii CNCM I-745 induces signalling via the mitogen-activated protein kinase pathway. In addition, effects on the phosphatidylinositol-3 kinase (PI3K) pathway have been reported. As an additional direct effect, S. boulardii CNCM I-745 secretes certain enzymes, which enhance nutrient acquisition for the yeast and the host. The increased availability of digestive enzymes seems to be one of the mechanisms by which S. boulardii CNCM I-745 counteracts diarrhoea; however, also people with certain enzyme deficiencies may profit from its administration. More studies are needed to fully understand the mechanisms of trophic activation by the probiotic yeast.

Oil for the cancer engine: The cross-talk between oncogenic signaling and polyamine metabolism

The study of metabolism has provided remarkable information about the biological basis and therapeutic weaknesses of cancer cells. Classic biochemistry established the importance of metabolic alterations in tumor biology and revealed the importance of various metabolite families to the tumorigenic process. We have evidence of the central role of polyamines, small polycatonic metabolites, in cell proliferation and cancer growth from these studies. However, how cancer cells activate this metabolic pathway and the molecular cues behind the oncogenic action of polyamines has remained largely obscure. In contrast to the view of metabolites as fuel (anabolic intermediates) for cancer cells, polyamines are better defined as the oil that lubricates the cancer engine because they affect the activity of biological processes. Modern research has brought back to the limelight this metabolic pathway, providing a strong link between genetic, metabolic, and signaling events in cancer. In this review, we enumerate and discuss current views of the regulation and activity of polyamine metabolism in tumor cell biology.

Polyamines cause plasma membrane depolarization, activate Ca2+-, and modulate H+-ATPase pump activity in pea roots

Polyamines regulate a variety of cation and K(+) channels, but their potential effects on cation-transporting ATPases are underexplored. In this work, noninvasive microelectrode ion flux estimation and conventional microelectrode techniques were applied to study the effects of polyamines on Ca(2+) and H(+) transport and membrane potential in pea roots. Externally applied spermine or putrescine (1mM) equally activated eosin yellow (EY)-sensitive Ca(2+) pumping across the root epidermis and caused net H(+) influx or efflux. Proton influx induced by spermine was suppressed by EY, supporting the mechanism in which Ca(2+) pump imports 2 H(+) per each exported Ca(2+). Suppression of the Ca(2+) pump by EY diminished putrescine-induced net H(+) efflux instead of increasing it. Thus, activities of Ca(2+) and H(+) pumps were coupled, likely due to the H(+)-pump inhibition by intracellular Ca(2+). Additionally, spermine but not putrescine caused a direct inhibition of H(+) pumping in isolated plasma membrane vesicles. Spermine, spermidine, and putrescine (1mM) induced membrane depolarization by 70, 50, and 35 mV, respectively. Spermine-induced depolarization was abolished by cation transport blocker Gd(3+), was insensitive to anion channels' blocker niflumate, and was dependent on external Ca(2+). Further analysis showed that uptake of polyamines but not polyamine-induced cationic (K(+)+Ca(2+)+H(+)) fluxes were a main cause of membrane depolarization. Polyamine increase is a common component of plant stress responses. Activation of Ca(2+) efflux by polyamines and contrasting effects of polyamines on net H(+) fluxes and membrane potential can contribute to Ca(2+) signalling and modulate a variety of transport processes across the plasma membrane under stress.

Formation of ternary complexes with MgATP: effects on the detection of Mg2+ in biological samples by bidentate fluorescent sensors

Fluorescent indicators based on β-keto-acid bidentate coordination motifs display superior metal selectivity profiles compared to current o-aminophenol-N,N,O-triacetic acid (APTRA) based chelators for the study of biological magnesium. These low denticity chelators, however, may allow for the formation of ternary complexes with Mg(2+) and common ligands present in the cellular milieu. In this work, absorption, fluorescence, and NMR spectroscopy were employed to study the interaction of turn-on and ratiometric fluorescent indicators based on 4-oxo-4H-quinolizine-3-carboxylic acid with Mg(2+) and ATP, the most abundant chelator of biological magnesium, thus revealing the formation of ternary complexes under conditions relevant to fluorescence imaging. The formation of ternary species elicits comparable or greater optical changes than those attributed to the formation of binary complexes alone. Dissociation of the fluorescent indicators from both ternary and binary species have apparent equilibrium constants in the low millimolar range at pH 7 and 25 °C. These results suggest that these bidentate sensors are incapable of distinguishing between free Mg(2+) and MgATP based on ratio or intensity-based steady-state fluorescence measurements, thus posing challenges in the interpretation of results from fluorescence imaging of magnesium in nucleotide-rich biological samples.

Role of polyamines at the G1/S boundary and G2/M phase of the cell cycle

The role of polyamines at the G1/S boundary and in the G2/M phase of the cell cycle was studied using synchronized HeLa cells treated with thymidine or with thymidine and aphidicolin. Synchronized cells were cultured in the absence or presence of α-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, plus ethylglyoxal bis(guanylhydrazone) (EGBG), an inhibitor of S-adenosylmethionine decarboxylase. When polyamine content was reduced by treatment with DFMO and EGBG, the transition from G1 to S phase was delayed. In parallel, the level of p27(Kip1) was greatly increased, so its mechanism was studied in detail. Synthesis of p27(Kip1) was stimulated at the level of translation by a decrease in polyamine levels, because of the existence of long 5'-untranslated region (5'-UTR) in p27(Kip1) mRNA. Similarly, the transition from the G2/M to the G1 phase was delayed by a reduction in polyamine levels. In parallel, the number of multinucleate cells increased by 3-fold. This was parallel with the inhibition of cytokinesis due to an unusual distribution of actin and α-tubulin at the M phase. Since an association of polyamines with chromosomes was not observed by immunofluorescence microscopy at the M phase, polyamines may have only a minor role in structural changes of chromosomes at the M phase. In general, the involvement of polyamines at the G2/M phase was smaller than that at the G1/S boundary.

Calcium efflux systems in stress signaling and adaptation in plants

Transient cytosolic calcium ([Ca(2+)](cyt)) elevation is an ubiquitous denominator of the signaling network when plants are exposed to literally every known abiotic and biotic stress. These stress-induced [Ca(2+)](cyt) elevations vary in magnitude, frequency, and shape, depending on the severity of the stress as well the type of stress experienced. This creates a unique stress-specific calcium "signature" that is then decoded by signal transduction networks. While most published papers have been focused predominantly on the role of Ca(2+) influx mechanisms to shaping [Ca(2+)](cyt) signatures, restoration of the basal [Ca(2+)](cyt) levels is impossible without both cytosolic Ca(2+) buffering and efficient Ca(2+) efflux mechanisms removing excess Ca(2+) from cytosol, to reload Ca(2+) stores and to terminate Ca(2+) signaling. This is the topic of the current review. The molecular identity of two major types of Ca(2+) efflux systems, Ca(2+)-ATPase pumps and Ca(2+)/H(+) exchangers, is described, and their regulatory modes are analyzed in detail. The spatial and temporal organization of calcium signaling networks is described, and the importance of existence of intracellular calcium microdomains is discussed. Experimental evidence for the role of Ca(2+) efflux systems in plant responses to a range of abiotic and biotic factors is summarized. Contribution of Ca(2+)-ATPase pumps and Ca(2+)/H(+) exchangers in shaping [Ca(2+)](cyt) signatures is then modeled by using a four-component model (plasma- and endo-membrane-based Ca(2+)-permeable channels and efflux systems) taking into account the cytosolic Ca(2+) buffering. It is concluded that physiologically relevant variations in the activity of Ca(2+)-ATPase pumps and Ca(2+)/H(+) exchangers are sufficient to fully describe all the reported experimental evidence and determine the shape of [Ca(2+)](cyt) signatures in response to environmental stimuli, emphasizing the crucial role these active efflux systems play in plant adaptive responses to environment.

Molecular basis for chiral selection in RNA aminoacylation

The chiral-selective aminoacylation of an RNA minihelix is a potential progenitor to modern tRNA-based protein synthesis using l-amino acids. This article describes the molecular basis for this chiral selection. The extended double helical form of an RNA minihelix with a CCA triplet (acceptor of an amino acid), an aminoacyl phosphate donor nucleotide (mimic of aminoacyl-AMP), and a bridging nucleotide facilitates chiral-selective aminoacylation. Energetically, the reaction is characterized by a downhill reaction wherein an amino acid migrates from a high-energy acyl phosphate linkage to a lower-energy carboxyl ester linkage. The reaction occurs under the restriction that the nucleophilic attack of O, from 3′-OH in the terminal CCA, to C, from C=O in the acyl phosphate linkage, must occur at a Bürgi-Dunitz angle, which is defined as the O–C=O angle of approximately 105°. The extended double helical form results in a steric hindrance at the side chain of the amino acid leading to chiral preference combined with cation coordinations in the amino acid and the phosphate oxygen. Such a system could have developed into the protein biosynthetic system with an exclusively chiral component (l-amino acids) via (proto) ribosomes.

Conformations of spermine in adenosine triphosphate complex: the structural basis for weak bimolecular interactions of major cellular electrolytes

Selectively (2)H- and (13)C-labeled spermines (SPM) were efficiently synthesized and analyzed by NMR spectroscopy to determine the spin-spin coupling constants for six conformationally relevant bonds. SPM that is composed of three alkyl moieties, a butanylene, and two propanylene chains undergoes a conformational change when interacting with multivalent anions (e.g., adenosine triphosphate (ATP), ATP-Mg(2+) , and tripolyphosphate). Upon interaction with ATP, the C-C bonds, which affect the distance between the neighboring pairs of ammonium groups (i.e., N1/N5 and N5/N5'), increase the population of gauche rotamers by 17-20% relative to those in the 4 HCl salt of SPM. However, the trend in increments of the gauche conformers for the SPM-ATP complex profoundly differs from that of the spermidine (SPD)-ATP complex. This implies that SPM may preferentially recognize the adenyl group of ATP rather than the tripolyphosphate moiety. This may account for the higher affinity of SPM to ATP-Mg(2+) than with that of SPD, which chiefly interacts with β- and γ-phosphates and is easily replaced by Mg(2+) . These results may provide a clue for the further understanding of the structural basis of polyamine biological functions.

Elucidation of spermidine interaction with nucleotide ATP by multiple NMR techniques

Interaction of polyamines with nucleotides plays a key role in many biological processes. Here we use multiple NMR techniques to characterize interaction of spermidine with adenosine 5'-triphosphate (ATP). Two-dimensional (1)H-(15)N spectra obtained from gs-HMBC experiments at varied pH show significant shift of N-1 peak around pH 2.0-7.0 range, suggesting that spermidine binds to N-1 site of ATP base. The binding facilitates N-1 deprotonation, shifting its pK(a) from 4.3 to 3.4. By correlating (15)N and (31)P chemical shift data, it is clear that spermidine is capable of concurrently binding to ATP base and phosphate sites around pH 4.0-7.0. The self-diffusion constants derived from (1)H PFG-diffusion measurements provide evidence that binding of spermidine to ATP is in 1:1 ratio, and pH variations do not induce significant nucleotide self-association in our samples. (31)P spectral analysis suggests that at neutral pH, Mg(2+) ion competes with spermidine and shows stronger binding to ATP phosphates. From (31)P kinetic measurements of myosin-catalyzed ATP hydrolysis, it is found that binding of spermidine affects the stability and reactivity of ATP. These NMR results are important for advancing the studies on nucleotide-polyamine interaction and its impact on nucleotide structures and activities under varied conditions.

Modulation of cellular function by polyamines

Polyamines (putrescine, spermidine and spermine) are essential for normal cell growth. The polyamine levels in cells are regulated by biosynthesis, degradation, and transport. Polyamines can modulate the functions of DNA, nucleotide triphosphates, proteins, and especially RNA because most polyamines exist in a polyamine-RNA complex in cells. Thus, the major focus on this review is on the role of polyamines in protein synthesis. In addition, effects of polyamines on B to Z conversion of DNA, transcription, phosphorylation of proteins, cell cycle progression, apoptosis and ion channels, especially NMDA receptors, are outlined. The function of eIF5A is also briefly discussed. Finally, a correlation between acrolein, produced from polyamines by polyamine oxidases, and chronic renal failure or brain stroke is summarized. Increased levels of polyamine oxidases and acrolein are good markers of chronic renal failure and brain stroke.

Underivatized polyamine analysis in plant samples by ion pair LC coupled with electrospray tandem mass spectrometry

Polyamines are key regulators of cell development and many plant responses to environmental challenges, however, their functions still remain unclear in complex interactions with other hormones and in biotic or abiotic stress. This lack of knowledge derives from the difficulties on measuring natural polyamines in plants. Here, we present a fast multiresidue method for putrescine (Put), 1,3-diaminopropane (DAP), l-ornithine, spermidine (Spd) and spermine (Spn) measurements in plant samples. Polyamine determination is based on a perchloric acid extraction followed by a simple filtration procedure without previous derivatization. Polyamines are resolved by HPLC in a C18 common column and quantified by electrospray ionization tandem mass spectrometry. (13)C(4)-putrescine and 1,7-diaminoheptane standards were added prior to sample extraction to achieve an accurate quantification in a single run. Chromatography of polyamines presents poor retention when reverse phase C18 common columns are used, because they are very polar compounds and contain several positive charges. To circumvent this problem ionic pairing technique has been used successfully with heptafluorobutyric acid (HFBA) at 1mM in the aqueous phase and 25mM in the sample. Improvement of the signal depleted by HFBA has been achieved by adding 1% of propionic acid to the aqueous and organic eluents. All together, gives a method accurate enough to determine polyamines in plants. To demonstrate the usefulness of the method it has been validated in Arabidopsis thaliana samples and polyamines have been determined in several genotypes that over express (35S::ADC2 line 3.6) or are disrupted (adc2) in the Arginine Decarboxylase2 (ADC2) gene.

Conformational change of spermidine upon interaction with adenosine triphosphate in aqueous solution

Endogenous polyamines, represented by putrescine, spermidine, and spermine, are known to exert their physiological functions by interacting with polyanionic biomolecules such as DNA, RNA, adenosine triphosphate (ATP), and phospholipids. Very few examples of conformation analysis have been reported for these highly flexible polymethylene compounds, mainly due to the lack of appropriate methodologies. To understand the molecular basis of the weak interaction between polyamines and polyanions that underlies their physiological functions, we aimed to elucidate the solution conformation of spermidine by using diastereospecifically deuterated and (13)C-labeled derivatives (1-7), which were designed to diagnose the orientation of seven conformationally relevant bonds in spermidine. (1)H-(1)H and (13)C-(1)H NMR coupling constants ((3)J(H,H) and (3)J(C,H)) were successfully determined for a spermidine-ATP complex. The relevant coupling constants markedly decreased upon complexation. The results reveal that spermidine, when interacting with ATP, undergoes changes that make the conformation more bent and forms the complex with the triphosphate part of ATP in an orientation-sensitive manner.

Cardiac IK1 underlies early action potential shortening during hypoxia in the mouse heart

It is established that prolonged hypoxia leads to activation of K(ATP) channels and action potential (AP) shortening, but the mechanisms behind the early phase of metabolic stress remain controversial. Under normal conditions IK1 channels are constitutively active while K(ATP) channels are closed. Therefore, early changes in IK1 may underlie early AP shortening. This hypothesis was tested using transgenic mice with suppressed IK1 (AAA-TG). In isolated AAA-TG hearts AP shortening was delayed by approximately 24 s compared to WT hearts. In WT ventricular myocytes, blocking oxidative phosphorylation with 1 mM cyanide (CN; 28 degrees C) led to a 29% decrease in APD90 within approximately 3-5 min. The effect of CN was reversed by application of 100 microM Ba2+, a selective blocker of IK1, but not by 10 microM glybenclamide, a selective blocker of KATP channels. Accordingly, voltage-clamp experiments revealed that both CN and true hypoxia lead to early activation of IK1. In AAA-TG myocytes, neither CN nor glybenclamide or Ba2+ had any effect on AP. Further experiments showed that buffering of intracellular Ca2+ with 20 mM BAPTA prevented IK1 activation by CN, although CN still caused a 54% increase in IK1 in a Ca2+ -free bath solution. Importantly, both (i) 20 microM ruthenium red, a selective inhibitor of SR Ca2+ -release, and (ii) depleting SR by application of 10 microM ryanodine+1 mM caffeine, abolished the activation of IK1 by CN. The above data strongly argue that in the mouse heart IK1, not KATP, channels are responsible for the early AP shortening during hypoxia.

Dendritic receptors designed to bind polyanions in both organic and aqueous media

This paper reports the synthesis of dendrons containing a spermine unit at their focal point. The dendritic branching is based on l-lysine building blocks, and has terminal oligo(ethyleneglycol) units on the surface. As a consequence of the solubilising surface groups, these dendrons have high solubility in solvents with widely different polarities (e.g., dichloromethane and water). The protonated spermine unit at the focal point is an effective anion binding fragment and, as such, these dendrons are able to bind to polyanions. This paper demonstrates that polyanions can be bound in both dichloromethane (using a dye solubilisation assay) and in water (competitive ATP binding assay). In organic media the dendritic branching appears to have a pro-active effect on the solubilisation of the dye, with more dye being solubilised by higher generations of dendron. On the other hand, in water the degree of branching has no impact on the anion binding process. We propose that in this case, the spermine unit is effectively solvated by the bulk solvent and the dendritic branching does not need to play an active role in assisting solubility. Dendritic effects on anion binding have therefore been elucidated in different solvents. The dendritic branching plays a pro-active role in providing the anion binding unit with good solubility in apolar solvent media.

Novel oral formulation safely improving intestinal absorption of poorly absorbable drugs: Utilization of polyamines and bile acids

In order to develop a novel oral formulation that can safely improve the intestinal absorption of poorly absorbable drugs, polyamines such as spermine (SPM) and spermidine (SPD) was examined as an absorption enhancing adjuvant in rats. The absorption of rebamipide, classified into BCS Class IV, from colon was significantly improved by SPM or SPD, and the enhancing ability of SPM was larger than that of SPD. As a possible mixing and/or interaction of polyamines with bile acids were expected, the combinatorial use of sodium taurocholate (STC) with polyamines was also examined. The absorption of rebamipide was drastically improved by the combinatorial use of SPM or SPD with STC. As STC itself did not enhance the absorption of rebamipide so much, it was considered that polyamines and STC had a synergistic enhancing effect. In-vivo oral absorption study was also performed to investigate the effectiveness and safety of polyamines and their combinatorial use with STC in rats. Although the enhancing effect slightly attenuated comparing with the in-situ loop study, the absorption of rebamipide was significantly improved and the combinatorial use of 10 mM SPM with 25 mM STC showed the largest enhancing effect. Histopathological studies clearly showed that any significant change in stomach and duodenum was not caused by SPM (10 mM), SPD (10 mM) or their combinatorial use with STC (25 mM) at 1.5 or 8.0 h after oral administration. Taken all together, polyamines, especially SPM, and its combinatorial use with STC could improve the absorption of poorly absorbable drugs without any significant changes in gastrointestinal tract after oral administration in rats.

Regulatory role of polyamine in the acid phosphatase from potato tubers

Effects of polyamine and metal ions on the new type of acid phosphatase purified from potato (Solanum tuberosum L. Irish Cobbler) tubers were analyzed. The enzyme belongs to nonspecific acid phosphatase family (EC 3.1.3.2), which hydrolyzes various phosphorylated substrates. The enzyme hydrolyzed inorganic pyrophosphate as a preferred substrate, and exhibited the hyperbolic kinetics with respect to the substrate, inorganic pyrophosphate in the absence of metal cations. Polyamine activated the enzyme effectively by lowering the K(m) value without appreciable changes in the maximal velocity. The most effective polyamines as activators were spermine and spermidine. Mg(2+) ion increased the K(m) value without affecting the maximal velocity of the enzyme, but Ca(2+) ion decreased both the K(m) and V(max) values. Increasing concentrations of spermine also decreased the K(m) value irrespective of Mg(2+) ion included, but gave a constant K(m) and V(max) values in the absence and presence of Ca(2+) ion. Action of spermine and metal ions can be explained by the complex formation with the substrate pyrophosphate. The acid phosphatase from potato can utilize the pyrophosphate-spermine or pyrophosphate-Ca(2+) complex as the preferred substrates. However, the enzyme can use the pyrophosphate-Mg complex with a weak affinity for the active site. Polyamine activates acid phosphatase in the absence and presence of metal cations, and activation by polyamine of the enzyme may contribute to the stimulation of starch biosynthesis and the control of glycolysis/gluconeogenesis by regulating PPi levels in growing potato tubers.

Polyamines modify the components of phospholipids-based signal transduction pathway in Coffea arabica L. cells

Recent results, fundamentally obtained from animal tissues, suggest that polyamines (Pas), essential compounds for the growth and development of all life organisms, may interact with a signal transduction cascade. Because Pas are highly positive charged compounds, their binding with phospholipids involved in signal transduction is likely to be the case. In this work, the in vivo effect of Pas on some important components of phospholipid signal transduction pathway was studied, by the first time, in plant tissue. Endogenous Pas content varied during the culture cycle of Coffea arabica cells: putrescine (Put) levels increased at the end of the stationary phase, both spermidine (Spd) and spermine (Spm) accumulated at the beginning of the linear growth phase. Cells that were incubated with Put presented a significant increase in phospholipase D (PLD) (EC: 3.1.4.4) activity, phospholipase C (PLC) (EC: 3.1.4.3) activity decreased, and the effect on lipid kinases was less marked. However, the incubation of the cells with Spd and Spm significantly stimulated the lipid kinases activities, fundamentally increased the formation of phosphatidyl inositol 4-phosphate (PIP) and phosphatidylinositol 4,5-bisphosphate (PIP2), while the effect on PLC and PLD activities was minor when compared with the cells treated with Put. The results presented here suggest that Pas may modulate the cellular signal of C. arabica cells by differentially affecting components of the phospholipid cascade.

Chain termination and inhibition of Saccharomyces cerevisiae poly(A) polymerase by C-8-modified ATP analogs

The nucleotide substrate specificity of yeast poly(A) polymerase (yPAP) toward various C-2- and C-8-modified ATP analogs was examined. 32P-Radiolabeled RNA oligonucleotide primers were incubated with yPAP in the absence of ATP to assay polyadenylation using unnatural ATP substrates. The C-2-modified ATP analogs 2-amino-ATP and 2-chloro (Cl)-ATP were excellent substrates for yPAP. 8-Amino-ATP, 8-azido-ATP, and 8-aza-ATP all produced chain termination of polyadenylation, and no primer extension was observed with the C-8-halogenated derivatives 8-Br-ATP and 8-Cl-ATP. The effects of modified ATP analogs on ATP-dependent poly(A) tail synthesis by yPAP were also examined. Whereas C-2 substitution (2-amino-ATP and 2-Cl-ATP) had little effect on poly(A) tail length, C-8 substitution produced moderate (8-amino-ATP, 8-azido-ATP, and 8-aza-ATP) to substantial (8-Br-ATP and 8-Cl-ATP) reduction in poly(A) tail length. To model the biochemical consequences of 8-Cl-Ado incorporation into RNA primers, a synthetic RNA primer containing a 3'-terminal 8-Cl-AMP residue was prepared. Polyadenylation of this modified RNA primer by yPAP in the presence of ATP was blocked completely. To probe potential mechanisms of inhibition, two-dimensional NMR spectroscopy experiments were used to examine the conformation of two C-8-modified AMP nucleotides, 8-Cl-AMP and 8-amino-AMP. C-8 substitution in adenosine analogs shifted the ribose sugar pucker equilibrium to favor the DNA-like C-2'-endo form over the C-3'-endo (RNA-like) conformation, which suggests a potential mechanism for polyadenylation inhibition and chain termination. Base-modified ATP analogs may exert their biological effects through polyadenylation inhibition and thus may provide useful tools for investigating polyadenylation biochemistry within cells.

Localization of arginine decarboxylase in tobacco plants

The lack of knowledge about the tissue and subcellular distribution of polyamines (PAs) and the enzymes involved in their metabolism remains one of the main obstacles in our understanding of the biological role of PAs in plants. Arginine decarboxylase (ADC; EC 4.1.1.9) is a key enzyme in polyamine biosynthesis in plants. We have characterized a cDNA coding for ADC from Nicotiana tabacum L. cv. Petit Havana SR1. The deduced ADC polypeptide had 721 amino acids and a molecular mass of 77 kDa. The ADC cDNA was overexpressed in Escherichia coli, and the ADC fusion protein obtained was used to produce polyclonal antibodies. Using immunological methods, we demonstrate the presence of the ADC protein in all plant organs analysed: flowers, seeds, stems, leaves and roots. Moreover, depending on the tissue, the protein is localized in two different subcellular compartments, the nucleus and the chloroplast. In photosynthetic tissues, ADC is located mainly in chloroplasts, whereas in non-photosynthetic tissues the protein appears to be located in nuclei. The different compartmentation of ADC may be related to distinct functions of the protein in different cell types.

Spermine increases phosphatidylinositol 4,5-bisphosphate content in permeabilized and nonpermeabilized HL60 cells

The polyamine spermine (N,N'bis[3-aminopropyl]-1,4-butanediamine) activates phosphatidylinositol-4-phosphate 5-kinase (PtdIns(4)P5K) and phosphatidylinositol 4-kinase (PtdIns4K) in vitro. Spermine concentration increases that occur in proliferating cells were approximated in streptolysin O-permeabilized HL60 cells. When phospholipase C was activated by GTPgammaS in the presence of PITPalpha, 0.1-1.2 mM spermine evoked increases in PtdIns(4,5)P(2) contents in a dose-dependent manner to 110-170% of control and concomitantly decreased inositol phosphate formation by 10-50%. Spermine-induced increases in PtdIns(4,5)P(2) content in permeabilized cells also occurred during GTPgammaS stimulation in the absence of PITPalpha, were augmented in the presence of PITPalpha, occurred in unstimulated cells and were additive to PtdIns(4,5)P(2) formation evoked by ARF1, another activator of phosphoinositide kinases. Slowly developing spermine-evoked increases in PtdIns(4,5)P(2) contents occurred in nonpermeabilized cells that were abolished in the presence of a spermine transport inhibitor. Data are consistent with spermine at physiological concentrations evoking a PITPalpha-dependent shift in formation of PtdIns(4,5)P(2) from compartments that contained an active phospholipase C to compartments that were separated from an active PLC and from PtdIns(4,5)P(2) formed by ARF1.

Effect of polyamines on mesangial cell ecto-5'-nucleotidase and ecto-ATPase activity

Polyamines were found to modulate the activity of several membrane-bound enzymes, participating in cell growth and differentiation. We have studied the effect of polyamines (spermidine, spermine and putrescine) on rat mesangial cell ectoenzymes: 5'-nucleotidase, Mg(2+)-ATPase and Ca(2+)-ATPase. Ecto-5'-nucleotidase activity was significantly increased after 48 h treatment with spermine and spermidine. Mg(2+)-ATPase was increased only after treatment with spermidine; however, Ca(2+)-ATPase was significantly increased after both spermine and spermidine treatment of mesangial cells. Culture of mesangial cells with putrescine did not change the activity of these ectoenzymes. Increased expression of mesangial cell ecto-ATPase and ecto-5'-nucleotidase after spermine and spermidine treatment could result in an increased production of adenosine, a powerful autacoid interesting with respect to a role of mesangial cells in inflammatory processes.

Polyamines interact with DNA as molecular aggregates

New compounds, named nuclear aggregates of polyamines, having a molecular mass of 8000, 4800 and < 1000 Da, were found in the nuclear extracts of several replicating cells. Their molecular structure is based on the formation of ionic bonds between polyamine ammonium and phosphate groups. The production of the 4800 Da compound, resulting from the aggregation of five or more < 1000 Da units, was increased in Caco-2 cells treated with the mitogen gastrin. Dissolving single polyamines in phosphate buffer resulted in the in vitro aggregation of polyamines with the formation of compounds with molecular masses identical to those of natural aggregates. After the interaction of the 4800 Da molecular aggregate with the genomic DNA at 37 degrees C, both the absorbance of DNA in phosphate buffer and the DNA mobility in agarose gel increased greatly. Furthermore, these compounds were able to protect the genomic DNA from digestion by DNase I, a phosphodiesterasic endonuclease. Our data indicate that the nuclear aggregate of polyamines interacts with DNA phosphate groups and influence, more efficaciously than single polyamines, both the conformation and the protection of the DNA.

Properties of a revertant of Escherichia coli viable in the presence of spermidine accumulation: increase in L-glycerol 3-phosphate

Escherichia coli CAG2242 cells are deficient in the speG gene encoding spermidine acetyltransferase. When these cells were cultured in the presence of 0.5 to 4 mM spermidine, their viability was greatly decreased through the inhibition of protein synthesis by overaccumulation of spermidine. When the cells were cultured with a high concentration of spermidine (4 mM), a revertant strain was obtained. We found that a 55-kDa protein, glycerol kinase, was overexpressed in the revertant and that synthesis of a ribosome modulation factor and the RNA polymerase sigma(38) subunit, factors important for cell viability, was increased in the revertant. Levels of L-glycerol 3-phosphate also increased in the revertant. Transformation of glpFK, which encodes a glycerol diffusion facilitator (glpF) and glycerol kinase (glpK), to E. coli CAG2242 partially prevented the cell death caused by accumulation of spermidine. It was also found that L-glycerol 3-phosphate inhibited spermidine binding to ribosomes and attenuated the inhibition of protein synthesis caused by high concentrations of spermidine. These results indicate that L-glycerol 3-phosphate reduces the binding of excess amounts of spermidine to ribosomes so that protein synthesis is recovered.

Investigation of the ternary D-myo-inositol 1,2,6-tris(phosphate)-spermine-Zn2+ system in solution

Interactions of Ins(1,2,6)P3 (IP), with spermine (Spm) and zinc cations have been studied by potentiometric and 31P NMR titrations. In the 4-11 pH range, two IPSpmZn2H3 and IPSpmZn2H mixed complexes are formed which are largely predominant with respect to the binary species. According to 31P NMR titration it is likely that one of the zinc cations preferably binds phosphates P1 and P6. The adduct formation between Ins(1,2,6)P3 and spermine seems also favourable to the formation of the mixed complexes. The occurrence of ternary complexes involving inositol-phosphates, biogenic amines, and metallic cations may be of relevance in the regulation of biological processes.

Destabilization of neutrophil NADPH oxidase by ATP and other trinucleotides and its prevention by Mg(2+)

Neutrophil NADPH oxidase (O(2)(-) generating enzyme) activated in a cell-free system was deactivated by dilution. When ATP was included in dilution the deactivation was further accelerated. The deactivation by dilution was biphasic, and the half-life of the enzyme was significantly shortened by ATP in each phase. ADP and AMP had little effect on the enzyme longevity while GTP and CTP had a similar effect to ATP. Staurosporine, a wide-range inhibitor of protein kinases, had no effect on ATP-induced deactivation, suggesting that the effect was not due to a protein phosphorylation. Mg(2+) addition largely prevented the deactivation by ATP. Chemical crosslinking of the activated oxidase prevented the deactivation by dilution and ATP, suggesting that the deactivation is caused by dissociation of the oxidase complex. Estimation of actin filament (F-actin) showed that the F-actin level was markedly reduced by addition of ATP. The ATP effect on the deactivation was not prominent in a semi-recombinant system which does not contain cytosol. These results suggest that ATP-induced deactivation is largely due to the chelation of Mg(2+) and are consistent with the concept that Mg(2+) stabilizes the oxidase complex by stabilizing F-actin.

Polyamines: mysterious modulators of cellular functions

In recent years the functions of polyamines (putrescine, spermidine, and spermine) have been studied at the molecular level. Polyamines can modulate the functions of RNA, DNA, nucleotide triphosphates, proteins, and other acidic substances. A major part of the cellular functions of polyamines can be explained through a structural change of RNA which occurs at physiological concentrations of Mg(2+) and K(+) because most polyamines exist in a polyamine-RNA complex within cells. Polyamines were found to modulate protein synthesis at several different levels including stimulation of special kinds of protein synthesis, stimulation of the assembly of 30 S ribosomal subunits and stimulation of Ile-tRNA formation. Effects of polyamines on ion channels have also been reported and are gradually being clarified at the molecular level.