Unique guanidine-conjugated catechins from the leaves of Alchornea rugosa and their autophagy modulating activity

Natural guanidines, molecules that contain the guanidine moiety, are structurally unique and often exhibit potent biological activities. A phytochemical investigation of the leaves of Alchornea rugosa (Lour.) Müll.Arg. by MS/MS-based molecular networking revealed eight undescribed guanidine-flavanol conjugates named rugonines A-H. The chemical structures of the isolated compounds were comprehensively elucidated by NMR spectroscopy, HRESIMS, and circular dichroism (CD) analysis. All isolated compounds were tested for autophagosome formation in HEK293 cells stably expressing GFP-LC3. The results revealed that compounds rugonines D-G showed potential autophagy inhibitory activity.

Guanidine Biosensors Enable Comparison of Cellular Turn-on Kinetics of Riboswitch-Based Biosensor and Reporter

Cell-based sensors are useful for many synthetic biology applications, including regulatory circuits, metabolic engineering, and diagnostics. While considerable research efforts have been made toward recognizing new target ligands and increasing sensitivity, the analysis and optimization of turn-on kinetics is often neglected. For example, to our knowledge there has been no systematic study that compared the performance of a riboswitch-based biosensor versus reporter for the same ligand. In this study, we show the development of RNA-based fluorescent (RBF) biosensors for guanidine, a common chaotropic agent that is a precursor to both fertilizer and explosive compounds. Guanidine is cell permeable and nontoxic to E. coli at millimolar concentrations, which in contrast to prior studies enabled direct activation of the riboswitch-based biosensor and corresponding reporter with ligand addition to cells. Our results reveal that the biosensors activate fluorescence in the cell within 4 min of guanidine treatment, which is at least 15 times faster than a reporter derived from the same riboswitch, and this rapid sensing activity is maintained for up to 1.6 weeks. Together, this study describes the design of two new biosensor topologies and showcases the advantages of RBF biosensors for monitoring dynamic processes in cell biology, biotechnology, and synthetic biology.

Guanidinium chloride-induced spectral perturbations of 4,4'-dianilino-1,1'-binaphthyl-5,5'-disulfonic acid confound interpretation of data on molten globule states

We describe limitations in the use of 4,4'-dianilino-1,1'-binaphthyl-5,5'-disulfonic acid (bis-ANS) to examine unfolding intermediates associated with guanidinium chloride (GuHCl)-induced protein denaturation. Several studies have used alterations in fluorescence emission of bis-ANS to quantify the population of "molten globule" states. Our findings indicate that the observed changes in bis-ANS spectroscopic properties could originate from the interactions of bis-ANS and GuHCl and the aggregation of the dye at higher GuHCl concentrations. We posit that in the absence of additional complementary structural or spectroscopic measurements, the use of bis-ANS emission alone to monitor protein conformations can be misleading.

Effects of energy restriction and fish oil supplementation on renal guanidino levels and antioxidant defences in aged lupus-prone B/W mice

Energy restriction (ER) and dietary fish oil (FO) are known to reduce the severity of glomerulonephritis and increase the lifespan of lupus-prone (NZB×NZW) F1(B/W) mice. In the present study, mice were fed eitherad libitumor energy-restricted (a 40 % lower energy intake than the dietad libitum), semi-purified diets containing 5 % maize oil or 5 % fish oil supplementation. To estimate the renal damage associated with oxidative stress, the total amounts of reactive oxygen species (ROS), cyclooxygenase-derived ROS and levels of guanidino compounds were measured. Additionally, we assessed the putative action of ER and FO on several key antioxidant enzymes measured in the kidney post-mitochondrial fraction. Results showed that the age-related increase in creatinine level was significantly reduced by ER and FO in old mice. In contrast, arginine and guanidino acetic acid levels showed a decrease with age but were increased by ER and FO. The GSH:GSSG ratio showed a significant decrease with age, whereas ER and FO feeding prevented the decrease. The age-related decrease in antioxidant scavenging superoxide dismutase, catalase and glutathione peroxidase activities were all reversed by ER and FO. The moderately decreased glutathione reductase and glutathione-S-transferase activities with age were significantly increased by ER and FO. Furthermore, the increased total ROS and cyclooxygenase-derived ROS levels were effectively reduced by ER and FO. In conclusion, our data strongly indicate that ER and FO maintain antioxidant status and GSH:GSSG ratio, thereby protecting against renal deterioration from oxidative insults during ageing.

Characterization of specific noncovalent complexes between guanidinium derivatives and single-stranded DNA by MALDI

Noncovalently bound complexes between highly basic sites of 12 guanidinium compounds and single-stranded DNA were studied using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. 6-Aza-2-thiothymine (ATT) was used as the matrix in the presence of ammonium citrate, and spectra were recorded in the positive ion mode. Detailed control experiments confirmed unambiguously the high selectivity and specificity of the guanidinium moiety for phosphate groups of DNA. The results verify the binding stoichiometry and show preferential binding of hydrophobic binders (pyrene and anthracene guanidinium derivatives) to all sequences examined. In addition, we demonstrate that electrostatic noncovalent interactions are strengthened with phosphorothioate analogs of DNA. These results clearly highlight the structure-directing role of the self-assembling organic species and strongly emphasize the significance of concentration, hydrophobicity, hydrogen-bonding, and pi-pi interactions of the artificial receptor in the formation of these noncovalent complexes. Because of the ability of DNA-binding compounds to influence gene expression, and therefore cell proliferation and differentiation, the interactions described above could be important in providing a better understanding of the mechanism of action of these noncovalent genetic regulators.

Analysis of guanidine in high salt and protein matrices by cation-exchange chromatography and UV detection

A simple and sensitive HPLC method for quantitative determination of guanidine in high salt and protein matrices was developed. The HPLC system consisted of an Agilent 1100 pump with an online degasser, a UV detector, an autosampler, and Dionex CS 14 cation-exchange guard (4 mm x 50 mm) and analytical (4 mm x 250 mm) columns. The mobile phase was 3.75 mM methanesulfonic acid (MSA) with a flow rate of 1 mL/min. The other analysis parameters were: 50 microL injection volume, 195 nm UV detection, and 21 min runtime. The limit of quantitation (LOQ) for guanidine HCl was determined to be 0.25 mg/L and the standard curve ranged from 0.25 mg/L to 10 mg/L. Sample preparation was required for the samples containing high protein concentrations. Proteins were removed by centrifuging a sample in a 30 K NanoSep centrifugal filter at 15,300 x g for 20 min. The method could determine guanidine accurately in sample matrices containing up to 200 mM sodium ion or up to 50 mM potassium ion. The method can be used for clearance testing of guanidine in biopharmaceutical products.

Improved high-performance liquid chromatographic determination of guanidino compounds by pre-column dervatization with ninhydrin and fluorescence detection

Ninhydrin has been investigated as a pre-column derivatization reagent for guanidino compounds. The reaction takes place under strongly alkaline conditions, followed by a second step at low pH and elevated temperature. This procedure yields derivatives with favourable fluorescence properties (excitation at 390 nm, emission at 470 nm). Amino acids do not react with ninhydrin under these conditions so that the method can easily be used for biological samples. Reversed-phase HPLC separations of the derivatives of several representative guanidino compounds in human blood have been achieved with gradients consisting of aqueous formic acid and methanol. Fluorescence detection yields quantification limits of about 20 microg L(-1). Hyphenation with electrospray mass spectrometry has been used to confirm the identity of the derivatives.

Thermodynamic Analysis of Receptors Based on Guanidinium/Boronic Acid Groups for the Complexation of Carboxylates,α-Hydroxycarboxylates, and Diols: Driving Force for Binding and Cooperativity

The thermodynamics of guanidinium and boronic acid interactions with carboxylates, alpha-hydroxycarboxylates, and diols were studied by determination of the binding constants of a variety of different guests to four different hosts (7-10). Each host contains a different combination of guanidinium groups and boronic acids. The guests included molecules with carboxylate and/or diol moieties, such as citrate, tartrate, and fructose, among others. The Gibbs free energies of binding were determined by UV/Vis absorption spectroscopy, by use of indicator displacement assays. The receptor based on three guanidinium groups (7) was selective for the tricarboxylate guest. The receptors that incorporated boronic acids (8-10) had higher affinities for guests that included alpha-hydroxycarboxylate and catechol moieties over guests containing only carboxylates or alkanediols. Isothermal titration calorimetry revealed the enthalpic and entropic contributions to the Gibbs free energies of binding. The binding of citrate and tartrate was investigated with hosts 7-10, for which all the binding events were exothermic, with positive entropy. Because of the selectivity of hosts 8-10, a simple boronic acid (14) was also investigated and determined to be selective for alpha-hydroxycarboxylates and catechols over amino acids and alkanediols. Further, the cooperativity of 8 and 9 in binding tartrate was also investigated, revealing little or no cooperativity with 8, but negative cooperativity with 9. A linear entropy/enthalpy compensation relationship for all the hosts 7-10, 14, and the carboxylate-/diol-containing guests was also obtained. This relationship indicates that increasing enthalpy of binding is offset by similar losses in entropy for molecular recognition involving guanidinium and boronic acid groups.

Small amounts of urea and guanidine hydrochloride can be detected by a far-UV spectrophotometric method in dialysed protein solutions

The quantization of small amounts of chemical denaturants as urea or guanidine hydrochloride in protein solutions after dialysis is a difficult task in the molecular biology laboratory practice. Refractometric methods are useful to quantify a denaturant in the molar range but this methodology is not helpful when the denaturant is present in small amounts. The method herein described is a new comparative method that requires, a priori, the quantification of the stock solutions of urea (8 M) and guanidine hydrochloride (6 M) by refractometry to prepare by sequential dilution the standards used for comparison in the spectropolarimeter. The method is based on the observation that the wavelengths, at which the absorbance of polarized light increases in the far-UV region, as observed by spectropolarimetry, is related to the concentration of the chemical denaturant present in the protein solution. In the quantitation method herein reported, the urea and guanidine hydrochloride detection limits range from 1.2 x 10(-4) to 6 x 10(-6) M depending on the protein dialysis buffer used for a standard cell path length of 1 cm. The sensibility of this method results to be comprised in a range 4-5 orders of magnitude higher than that measured by refractometry. The determinations in both the sample and the control preparations are virtually completed within approximately 10 min.

Determination of DNA guanine sites forming photo-adducts with Ru(II)-labeled oligonucleotides; DNA polymerase inhibition by the resulting photo-crosslinking

The influence of the distance between the anchoring site of the tethered [Ru(TAP)(2)dip](2+) complex (TAP=1,4,5,8-tetraazaphenanthrene; dip=4,7-diphenyl-1,10-phenanthroline) on a probe sequence and the guanines of the complementary target strand was studied by (1) the luminescence quenching of the complex (by electron transfer) and (2) the oligodeoxyribonucleotide adduct (ODN adduct) formation which results in photo-crosslinking of the two strands. Moving the guanine moieties away from the complex induces an important decrease of the efficiency of both processes, but clearly affects the ODN adduct formation more specifically than the quenching process. From these results, we determined the positions of the guanine bases in the duplex ODN that are able to form a photo-adduct with the tethered complex. We also examined the possible competition between a long-range hole migration in the duplex ODN and the formation of a photo-adduct by using a sequence labeled with the complex at the 5'-phosphate end. Such a hole migration appears to be inefficient as compared to the ODN adduct formation. Finally, we studied the influence of the photo-crosslinking on the function of two different DNA polymerases. A 17-mer Ru(II)-labeled ODN was hybridized to its complementary sequence located on the 5'-side of a 40-mer matrix. After illumination, the elongation of a 13-mer DNA primer hybridized to the 3'-extremity of the same matrix was stopped at a position corresponding to the formation of the ODN adduct.

Probing of arginine residues in peptides and proteins using selective tagging and electrospray ionization mass spectrometry

A general labelling method is presented which allows the determination of the number of guanidine groups (related to arginine and homoarginine in peptides and proteins) by means of mass spectrometry. It implies a guanidine-selective derivatization step with 2,3-butanedione and an arylboronic acid under aqueous, alkaline conditions (pH 8-10). The reaction mixture is then directly analysed by electrospray ionization mass spectrometry without further sample pretreatment. Other amino acids are not affected by this reaction although it is demonstrated that lysine side-chains may be unambiguously identified when they are converted to homoarginine prior to derivatization. Guanidine functionalities, as e.g. in the amino acid arginine, are easily identified by the characteristic mass shift between underivatized and derivatized analyte. The tagging procedure is straightforward and selective for guanidine groups. The influence of several experimental parameters, especially the pH of the solution and the choice of reagents, is examined and the method is applied to various arginine-containing peptides and to lysozyme as a representative protein. Possible applications of this technique and its limitations are discussed.

Using analytical ultracentrifugation to study compositional variation in vertebrate genomes

Although much attention has recently been directed to analytical ultracentrifugation (AUC), the revival of interest has hardly addressed the applications of this technology in genome analysis, and the extent to which AUC studies can quickly and effectively complement modern sequence-based analyses of genomes, e.g. by anticipating, extending or checking results that can be obtained by cloning and sequencing. In particular, AUC yields a quick overview of the base compositional structure of a species' genome even if no DNA sequences are available and the species is unlikely to be sequenced in the near future. The link between AUC and DNA sequences dates back to 1959, when a precise linear relation was discovered between the GC (guanine+cytosine) level of DNA fragments and their buoyant density in CsCl as measured at sedimentation equilibrium. A 24-hour AUC run of a high molecular weight sample of a species' total DNA already yields the GC distribution of its genome. AUC methods based on this principle remain sensitive tools in the age of genomics, and can now be fine-tuned by comparing CsCl absorbance profiles with the corresponding sequence histograms. The CsCl profiles of vertebrates allow insight into structural and functional properties that correlate with base composition, and their changes during vertebrate evolution can be monitored by comparing CsCl profiles of different taxa. Such comparisons also allow consistency checks of phylogenetic hypotheses at different taxonomic levels. We here discuss some of the information that can be deduced from CsCl profiles, with emphasis on mammalian DNAs.

Species-specific PCR for the identification of ovine, porcine and chicken species in meta and bone meal (MBM)

BSE, first identified in the UK in 1986 is thought to have arisen from feeding scrapie infected Meat and Bone Meal (MBM), produced under sub-optimal conditions, to cattle. For quality and safety reasons there is a requirement for a good analytical test for the surveillance of processed MBM. This study describes species-specific PCR assays for the identification of ovine, porcine and poultry species in MBM. A comparison between two distinct DNA extraction methods, i.e. the silicaguanidiumthiocyanate DNA isolation procedure and a commercial DNA extraction kit, is also presented. Application of this technology to species identification in industrial MBM was investigates as part of this study.

[Solid-phase synthesis of peptides containing arginine with an unprotected guanidine group]

A new variant of the solid phase synthesis of arginine-containing peptides was proposed. The conditions for the attachment to the Wang polymer of N alpha-Fmoc-arginine containing a protonated guanidine group were found. We demonstrated that this attachment is accompanied by neither racemization nor the attachment of the second Arg residue. Side reactions involving the guanidine group of arginine were studied, and methods for their prevention were proposed. The comparison of the carbodiimide method with a 1-hydroxybenzotriazole additive and a modified method with the use of Kastro's reagent for the introduction of N alpha-Fmoc-Arg residue with the unprotected guanidine group into the growing peptide chain demonstrated the advantages of the second method. Bradykinin and a peptide corresponding to the 584-591 sequence of the transmembrane gp41 from HIV-1 were synthesized by the method proposed here.

DNA duplex dynamics: NMR relaxation studies of a decamer with uniformly 13C-labeled purine nucleotides

Dynamics in a DNA decamer duplex, d(CATTTGCATC). d(GATGCAAATG), were investigated via a detailed 13C NMR relaxation study. Every 2'-deoxyadenosine and 2'-deoxyguanidine was chemically enriched with 15% 13C and 98% 15N isotopes. Six nuclear relaxation parameters [R(13Cz), R(1Hz), R(2(1)Hz13Cz), R(13Cx), R(2(1)Hz13Cx) and steady-state 13C¿1H¿ NOE] were measured at 600 MHz and three were measured at 500 MHz (1H frequency) for the CH spin systems of sugar 1', 3', and 4' as well as base 8 and 2 positions. A dependence of relaxation parameter values on chemical position was clearly observed; however, no sequence-specific variation was readily evident within our experimental error of approximately 5-10%, except for 3' and 5' termini. It was demonstrated that the random 15% 13C enrichment effectively suppressed both scalar and dipolar contributions of the neighboring carbons and protons on the relaxation parameters. To analyze dynamics via all observed relaxation parameters, full spectral density mapping (1992, J. W. Peng and G. Wagner, J. Magn. Reson. 98, 308) and the "model-free" approach (1982, Lipari and Szabo, J. Am. Chem. Soc. 104, 4546) were applied complementarily. A linear correlation between three spectral density values, J(omegaC), J(omegaH - omegaC), and J(omegaH + omegaC) was observed in plots containing all measured values, but not for the other spectral density terms including J(0). These linear correlations reflect the effect of overall motion and similar internal motions for each CH vector in the decamer. The correlations yielded two correlation times, 3-4 ns and 10-200 ps. One value, 3-4 ns, corresponds to the value of 3.3 ns obtained for the overall isotropic tumbling correlation time determined from analysis of 13C T1/T2 ratios. The possibility of overall anisotropic tumbling was examined, but statistical analysis showed no advantage over the assumption of simple isotropic tumbling. Lack of correlations entailing J(0) implies that a relatively slow chemical exchange contributes to yielding of effective Jeff(0) values. Based on spectral density mapping and the T1/T2 ratio analysis, three basic assumptions were initially employed (and subsequently justified) for the model-free calculation: isotropic overall tumbling, one internal motion, and the presence of chemical exchange terms. Except for terminal residues, the order parameter S2 and the corresponding fast internal motion correlation time were determined to be about 0.8 +/- 0.1 and 20 +/- 20 ps, respectively, for the various CH vectors. Only a few differences were observed between or within sugars and bases. The internal motion is very fast (ps-ns time scale) and its amplitude restricted; e.g., assuming a simple wobble-in-a-cone model, the internal motion is restricted to an angular amplitude of +/-22. 5 degrees for each of the 1', 3', 4', 2, and 8 positions in the purine nucleotides in the entire duplex.

Endogenous recoveries and true ileal digestibilities of amino acids in newly weaned pigs fed diets with protease-treated soybean meal

Endogenous recoveries and true ileal digestibilities of amino acids were determined in pigs fed cornstarch-based diets with untreated or protease-treated soybean meal as protein sources. Twelve pigs, fitted with a modified post valve T-cecum cannula on d 14, 15, and 16 after birth, were weaned on d 20 and assigned to one of four diets according to a two-period balanced change-over design. Diets consisted of soybean meal 1) untreated (SBM), 2) incubated (1:2 wt/vol in distilled water adjusted to pH 4.5, for 16 h at 50 degrees C; CI-SBM), 3) sprayed with protease (1 microL/g of soybean meal; PS-SBM), and 4) incubated, as for CI-SBM, with protease in the water (PI-SBM) at the same application rate as that for PS-SBM. Each period consisted of 5 d of adaptation to diets followed by collection of ileal digesta on d 6 and 7 to determine the apparent ileal amino acid digestibilities of the diets. On d 9, guanidinated meals were fed, followed by a 24-h continuous collection of digesta. Recoveries of chromic oxide and dysprosium from the guanidinated meals were 96.0 +/- .5 and 94.5 +/- 1.1%, respectively. Endogenous amino acid recoveries were similar (P > .05) for SBM, CI-SBM, and PS-SBM but less (P < .05) for PI-SBM. True digestibilities were also less (P < .05) for PI-SBM than for the other meals. Recoveries of endogenous branched-chain and aromatic amino acids were less (P < .05) during Period 2 than during Period 1, suggesting dietary change- and(or) age-dependent adaptive increases in the secretions of pepsin and pancreatic proteases. In conclusion, protease treatment did not improve the true digestibilities of amino acids in soybean meal fed to newly weaned pigs.

Analysis of collagens solubilized from cartilage of normal and spontaneously osteoarthritic rhesus monkeys

Osteoarthritis (OA) is a disorder which results in the destruction of the articular cartilage and the remodeling of the subchondral bone in synovial joints. We have analyzed the cartilage collagen from normal and osteoarthritic free-ranging rhesus monkeys from the Cayo Santiago colony. The cartilage samples were assigned a severity score based on histological staging system and were divided into four groups (normals, mild OA, moderate OA and severe OA). After a 4.0 M guanidinium chloride (GuCl) extraction, the remainder of the cartilage was digested with pepsin and the collagen was salt precipitated at 2.5 M and 4.3 M NaCl. The GuCl solubility of the osteoarthritic cartilage increased compared to normals. Collagen extractability by GuCl also increased with the severity of disease. Pepsin digestion followed by salt precipitation shows that collagen from rhesus osteoarthritis cartilage is more easily extracted than from normal cartilage. With an anti-type I collagen antibody we have detected the presence of type I collagen in the severe OA cartilage samples but not in the milder OA groups or in normal cartilage. Total collagen content decreases with severity of OA, which is not due to changes in propyl hydroxylation because examination of collagen hydroxylation, based on hydroxyproline analysis, shows no difference between OA and normal cartilage.