Epigenetic studies in insects and the valproic acid perspective

Abstract Valproic acid in association with sodium valproate (VPA) is an important anticonvulsant drug used for decades to treat neurological disorders. VPA also acts as an epigenetic modulator by inhibiting histone deacetylases, permitting histone acetylation, affecting the DNA and histone methylation status and gene expression, and inducing chromatin remodeling. Insects represent an important animal model for studies in several areas of science. Their high phenotypic plasticity makes them alternative models for epigenetic studies. This brief review emphasizes recent reports on insect epigenetics and the contribution of studies on the VPA action in insects, including effects on epigenetic markers, extending the pharmacological understanding of the potential of this drug, and demonstrating the usefulness of insects as an alternative animal model to drug studies.

Nursing work process in Street Clinic to combat vulnerability of the Homeless Persons

Background

The Street Clinic was created to expand access to health for Homeless Persons. Within the service, the role of the nursing team is very important in accessing and establishing care, welcoming, bond building, promoting a save environment, health prevention and education, interdisciplinary communication, patient management and articulation with other services. The research aimed to analyze the objects, instruments, purposes and products in the nursing work process, considering the principle of equity of Brazilian National Health System and the serious vulnerability of the population in question. In this way, it is necessary to understand the valorization of nursing.

Methods

Study of qualitative approach with participant observation, field diary, application of three semi-structured interviews and use of thematic content analysis method. The study scenario was the nursing team of the Street Clinic in a city in the interior of São Paulo.

Results

The following elements of the nursing work process were analyzed: dwelling place, health demands and intersectionality of this population (objects); team organization, materials, harm reduction, communication with the intersectoral network, assistance, health guidance, opportunities for action, administration, management and personal and professional transformation (instruments); comprehensive and equitable care, building bonds and trust (purposes and products). Nursing, in this process and within a biomedical logic in the service, faces overload, pressure and devaluation.

Conclusions

Nursing is configured as a strategic category in the performance of the Street Clinic and in the equity of care. There are facilities and difficulties to act independently with the multiprofissional team, especially with the biomedical model present in the service. It is necessary to build recognition of the performance of nursing and the empowerment of professionals in this category.

Key messages

Nursing still needs professional empowerment and recognition of the importance of their work process as essential in addressing vulnerabilities and equity in care. Bonding, trust and harm reduction are essential elements in the nursing work process in addressing the vulnerability of the Homeless Persons.

Validation of Mycobacterium tuberculosis dihydroneopterin aldolase as a molecular target for anti-tuberculosis drug development

An early step of target validation in antimicrobial drug discovery is to prove that a gene coding for a putative target is essential for pathogen's viability. However, little attention has been paid to demonstrate the causal links between gene essentiality and a particular protein function that will be the focus of a drug discovery effort. This should be considered an important step in target validation since a growing number of proteins are found to exhibit multiple and unrelated tasks. Here, we show that the Mycobacterium tuberculosis (Mtb) folB gene is essential and that this essentiality depends on the dihydroneopterin aldolase/epimerase activities of its protein product, the FolB protein from the folate biosynthesis pathway. The wild-type (WT) MtFolB and point mutants K99A and Y54F were cloned, expressed, purified and monitored for the aldolase, epimerase and oxygenase activities using HPLC. In contrast to the WT MtFolB, both mutants have neither aldolase nor epimerase activities in the conditions assayed. We then performed gene knockout experiments and showed that folB gene is essential for Mtb survival under the conditions tested. Moreover, only the WT folB sequence could be used as a rescue copy in gene complementation studies. When the sequences of mutants K99A or Y54F were used for complementation, no viable colonies were obtained, indicating that aldolase and/or epimerase activities are crucial for Mtb survival. These results provide a solid basis for further work aiming to develop new anti-TB agents acting as inhibitors of the aldolase/epimerase activities of MtFolB.

Performance of Eriopis connexa (Coleoptera: Coccinellidae) resistant to lambda-cyhalothrin after extended recovery from knockdown

A population of the predatory lady beetle Eriopis connexa (Germar) (Coleoptera: Coccinellidae) was recorded as resistant to lambda-cyhalothrin. Adults exposed to this insecticide have recovered from knockdown after 72 h. Thus, the performance of resistant (R) and susceptible (S) populations of E. connexa not exposed to insecticide (R0 and S0) and R adults recovering from knockdown 24, 48, and 72 h after exposure (R24, R48, and R72) was studied. In addition, the fertility life table parameters were calculated for one generation considering the progenies from R0, S0, and R24 populations. The recovery rate from knockdown was 69.4% for R-adults, and greater recovery rate was observed within 48 h following lambda-cyhalothrin exposure. The S-females produced about 50% more eggs and lived longer, when compared with R-females irrespective of the recovery periods after knockdown. The R-females produced similar number of eggs and exhibited similar longevity across all treatments (R0, R24, R48, and R72). Progenies produced by R- and S-populations did not exhibit consistent differences in development and survival. The fertility life table parameters showed higher intrinsic rate of population growth (r_m) and lower mean generation time (T) for R0- and R24-females, when compared with those for S0-females. Thus, the time interval needed to recover from knockdown is not related to the adaptive cost of resistance in E. connexa.

Conformação de úbere de caprinos da raça Saanen: parâmetros estéticos ou funcionais?

RESUMODiversos fatores predisponentes são descritos para as afecções mamárias ou distúrbios secundários que comprometem a qualidade e produtividade de leite de fêmeas nas diferentes espécies. As características fenotípicas do úbere são consideradas na avaliação econômica de uma fêmea caprina, tanto pelo potencial de produção como pelo registro genealógico dessa fêmea. A limitação de estudos correlacionando essas características com a saúde do úbere gera a dúvida a respeito do significado da conformação do mesmo à saúde e produtividade da glândula mamária. Sendo assim, este estudo teve como objetivo relacionar os parâmetros da conformação do úbere com a celularidade da glândula mamária aferida pelo teste California Mastitis Test (CMT) e contagem de células somáticas (CCS) em 80 cabras da raça Saanen sem alterações no exame clínico da glândula mamária nem no teste de Tamis. Observou-se que a maioria dos parâmetros fenotípicos de úbere não influenciou a CCS, sendo considerados puramente estéticos. A circunferência e profundidade de úbere demonstraram correlação negativa com a celularidade e, por serem características de herdabilidade moderada a alta, podem ser parâmetros considerados para seleção genética de caprinos.

Lambda-Cyhalothrin Resistance in the Lady Beetle Eriopis connexa (Coleoptera: Coccinellidae) Confers Tolerance to Other Pyrethroids

Pyrethroid insecticides are widely recommended to control insect defoliators but lack efficacy against most aphid species. Thus, conserving aphid predators such as the lady beetle Eriopis connexa (Germar) is important to pest management in crop ecosystems that require pyrethroid sprays. In a greenhouse, early fourth-instar larvae and 5-day-old adults from susceptible (S) and resistant (R) E. connexa populations were caged on lambda-cyhalothrin-treated cotton plants, after which survival and egg production (for those caged at adult stage) were assessed. In the laboratory, similar groups were subjected to dried residues and topical treatment with one of eight pyrethroids (alpha-cypermethrin, bifenthrin, deltamethrin, esfenvalerate, fenpropathrin, permethrin, zeta-cypermethrin, and lambda-cyhalothrin), the organophosphate methidathion, or water and wetting agent. After caging on treated cotton terminals, 66% of the R-population larvae survived to adulthood, compared with 2% of those from the S-population. At 12 d after caging at adult stage under the same conditions, 64% of the females from the R-population survived and laid eggs, compared with 100% mortality and no oviposition for the S-females. In trials involving dried insecticide residues, gain in survival based on the survival difference (percentage for R-population minus percentage for S-population) across all tested pyrethroids varied from 3 to 63% for larvae and from 3 to 70% for adults. In trials involving topical sprays of the tested pyrethroids, survival differences ranged from 36 to 96% for larvae and from 21 to 82% for adults. Fenpropathrin and bifenthrin were the least and most toxic, respectively.

Characterization and screening of tight binding inhibitors of xanthine oxidase: an on-flow assay

On-flow characterization of tight binders of xanthine oxidase.

A low cost, safe, disposable, rapid and self-sustainable paper-based platform for diagnostic testing: lab-on-paper

There is a strong interest in the use of biopolymers in the electronic and biomedical industries, mainly towards low-cost applications. The possibility of developing entirely new kinds of products based on cellulose is of current interest, in order to enhance and to add new functionalities to conventional paper-based products. We present our results towards the development of paper-based microfluidics for molecular diagnostic testing. Paper properties were evaluated and compared to nitrocellulose, the most commonly used material in lateral flow and other rapid tests. Focusing on the use of paper as a substrate for microfluidic applications, through an eco-friendly wax-printing technology, we present three main and distinct colorimetric approaches: (i) enzymatic reactions (glucose detection); (ii) immunoassays (antibodies anti-Leishmania detection); (iii) nucleic acid sequence identification (Mycobacterium tuberculosis complex detection). Colorimetric glucose quantification was achieved through enzymatic reactions performed within specific zones of the paper-based device. The colouration achieved increased with growing glucose concentration and was highly homogeneous, covering all the surface of the paper reaction zones in a 3D sensor format. These devices showed a major advantage when compared to the 2D lateral flow glucose sensors, where some carryover of the coloured products usually occurs. The detection of anti-Leishmania antibodies in canine sera was conceptually achieved using a paper-based 96-well enzyme-linked immunosorbent assay format. However, optimization is still needed for this test, regarding the efficiency of the immobilization of antigens on the cellulose fibres. The detection of Mycobacterium tuberculosis nucleic acids integrated with a non-cross-linking gold nanoprobe detection scheme was also achieved in a wax-printed 384-well paper-based microplate, by the hybridization with a species-specific probe. The obtained results with the above-mentioned proof-of-concept sensors are thus promising towards the future development of simple and cost-effective paper-based diagnostic devices.

334 ADENOVIRAL VECTOR-MEDIATED EXPRESSION OF RECOMBINANT HUMAN GLUCOCEREBROSIDASE IN THE MAMMARY GLAND OF RATS

Glucocerebrosidase is a lysosomal enzyme that plays a key role in sphingolipid cleavage, an intermediate in glycolipid metabolism. A recessive mutation in the glucocerebrosidase gene leads to the accumulation of glucosylceramide in macrophages (sphingolipidosis), a lysosomal storage disease known in humans as the Gaucher disease. The enzyme replacement treatment with recombinant human glucocerebrosidase (hGCase) dramatically reduces and reverses symptoms, with the need of lifelong treatment for patients to attain a normal life. Currently, hGCase is very costly, being produced through in vitro expression in Chinese hamster ovary cells or in vivo, in plants. The aim of this study was to develop a model for the production of hGCase in the mammary gland of rats transiently transduced with recombinant adenovirus. A replication-defective adenovirus carrying hGCase was generated using the AdEasy™ adenoviral vector system (Stratagene, La Jolla, CA, USA). The hGCase cDNA (NM_001005741) was in vitro-synthesized and ligated in the XhoI site of the pAdTrack-CMV vector (pAdT-hGCase). The resulting plasmid was recombined with the pAdEasy™ vector in BJ5183 electro-competent cells. The purified pAdE-pAdT-hGCase vector was linearized and transfected into HEK-293 cells for the production of a primary viral stock. Further amplifications and the titration assay were done in HEK-293 cells, monitoring the transduction by the qualitative evaluation of green fluorescent protein (GFP) expression. Following transfection, the HEK-293 cells increasingly expressed the GFP reporter, regulated by a CMV promoter, in tandem with the hGCase cDNA, under another CMV promoter. On Day 18 of gestation, a female rat (Rattus norvegicus) was anesthetized and the 2 left caudal mammary glands were infused with 109 GTU mL–1 of the pAdE-pAdT-hGCase in PBS solution supplemented with 36 mM EGTA. The 2 right caudal mammary glands were infused only with PBS-EGTA (control milk). Milk samples collected from Days 2 through 9 post-partum were mixed with separation buffer (10 mM Tris-HCl, pH 8.0; 10 mM CaCl2) and centrifuged, with the supernatant assayed for hGCase by Western blot using a monoclonal anti-human glucocerebrosidase antibody (sc-166407, Santa Cruz Biotechnology, Santa Cruz, CA, USA). Relative quantification of the hGCase expression was done using the FluorChem FC2 system (Alpha Innotech, San Leandro, CA, USA), with hGCase band intensity being normalized against GAPDH expression. The in vivo expression assay confirmed the production of hGCase in the secreted portion of the rat milk, with a specific band between 50 to 60 kDa observed on the Western blot, and no detection of the protein in the control milk. The hGCase peak production occurred in Days 5 and 6 of lactation, with levels being 35 times greater than on Day 9. An ELISA quantification assay and an enzymatic activity assay for the recombinant hGCase are currently in development. In conclusion, the use of the rat for hGCase transient expression in the milk was proven a valid model for testing the potential use of a mammary gland expression system for the production of a functional human glucocerebrosidase protein.

Shikimate kinase (EC 2.7.1.71) from Mycobacterium tuberculosis: kinetics and structural dynamics of a potential molecular target for drug development

The enzymes of the shikimate pathway represent potential molecular targets for the development of non-toxic antimicrobial agents and anti-parasite drugs. One of the most promising of these enzymes is shikimate kinase (EC 2.7.1.71), which is responsible for the fifth step in the shikimate pathway. This enzyme phosphorylates shikimic acid to yield shikimate-3-phosphate, using ATP as a substrate. In this work, the conformational dynamics of the shikimate kinase from Mycobacterium tuberculosis was investigated in its apostate in solution. For this study, the enzyme was subjected to a gradient of temperatures from 15°C to 45°C in the presence or absence of deuterium oxide, and the amide H/D exchange was monitored using ESI-mass spectrometry. We observed: i) the phosphate binding domain in the apo-enzyme is fairly rigid and largely protected from solvent access, even at relatively high temperatures; ii) the shikimate binding domain is highly flexible, as indicated by the tendency of the apo-enzyme to exhibit large conformational changes to permit LID closure after the shikimate binding; iii) the nucleotide binding domain is initially conformationally rigid, which seems to favour the initial orientation of ADP/ATP, but becomes highly flexible at temperatures above 30°C, which may permit domain rotation; iv) part of the LID domain, including the phosphate binding site, is partially rigid, while another part is highly flexible and accessible to the solvent.

Latin American and Caribbean intercomparison of surface contamination monitoring equipment

In October 2009, the International Atomic Energy Agency (IAEA) sponsored an intercomparison exercise of surface contamination monitoring equipment, which was held at the Laboratório Nacional de Metrologia das Radiações Ionizantes, from the Instituto de Radioproteção e Dosimetria, IRD/CNEN, Rio de Janeiro. This intercomparison was performed to evaluate the calibration accessibility in Latin America and the Caribbean. Thirteen countries within the region and IAEA have sent instruments to be compared, but only five countries and IAEA were considered apt to participate. Analysis of instruments, results and discussions are presented and recommendations are drawn.

IAEA regional intercomparison of in vivo measurements of 131I in the thyroid: the Latin American and Caribbean experience

An in vivo intercomparison exercise, organised in the scope of the IAEA Regional Latin American (RLA) Project 9066, was carried out in 2009 aimed to harmonise measurement procedures on the measurement of (131)I in the thyroid among Latin American and Caribbean countries. The exercise consisted in the measurement of an anthropomorphic thyroid phantom spiked with a certified source of (133)Ba. The phantom was supplied by the In Vivo Monitoring Laboratory of Institute for Radiation Protection and Dosimetry (IRD) to 17 Institutions from 12 countries of the regions. Among these, 13 Institutions from 10 countries returned their measurement results as well as a standard report form containing detailed information about their respective counting facilities. All participants reported activities within an acceptable range, considering American National Standard Institute (ANSI) limits. Uncertainties varied from 0.04 to 12.9 %. Although results show that the general performance was acceptable in terms of accuracy, the need for additional action towards the standardisation of uncertainty estimation in this type of measurement in the region should be highlighted.

Structural bioinformatics study of PNP from Listeria monocytogenes

This work describes for the first time a model of Purine Nucleoside Phosphorylase from Listeria monocytogenes (LmPNP). We modeled the complexes of LmPNP with ligands in order to determine the structural basis for specificity. Comparative analysis of the model of LmPNP allowed identification of structural features responsible for ligand affinities.

Ab initio 3-D structure prediction of an artificially designed three-alpha-helix bundle via all-atom molecular dynamics simulations

The rate at which knowledge about genomic sequences and their protein products is produced is increasing much faster than the rate of 3-dimensional protein structure determination by experimental methods, such as X-ray diffraction and nuclear magnetic resonance. One of the major challenges in structural bioinformatics is the conversion of genomic sequences into useful information, such as characterization of protein structure and function. Using molecular dynamics (MD) simulations, we predicted the 3-dimensional structure of an artificially designed three- alpha -helix bundle, called A3, from a fully extended initial conformation, based on its amino acid sequence. The MD protocol enabled us to obtain the secondary, in 1.0 ns, as well as the supersecondary and tertiary structures, in 4.0-10.0 ns, of A3, much faster than previously described for a similar protein system. The structure obtained at the end of the 10.0-ns MD simulation was topologically a three-alpha-helix bundle.

Enoyl reductases as targets for the development of anti-tubercular and anti-malarial agents

Tuberculosis (TB) and Malaria are neglected diseases, which continue to be major causes of morbidity and mortality worldwide, killing together around 5 million people each year. Mycolic acids, the hallmark of mycobacteria, are high-molecular-weight alpha-alkyl, beta-hydroxy fatty acids. Biochemical and genetic experimental data have shown that the product of the M. tuberculosis inhA structural gene (InhA) is the primary target of isoniazid mode of action, the most prescribed anti-tubercular agent. InhA was identified as an NADH-dependent enoyl-ACP(CoA) reductase specific for long-chain enoyl thioesters and is a member of the Type II fatty acid biosynthesis system, which elongates acyl fatty acid precursors of mycolic acids. M. tuberculosis and P. falciparum enoyl reductases are targets for the development of anti-tubercular and antimalarial agents. Here we present a brief description of the mechanism of action of, and resistance to, isoniazid. In addition, data on inhibition of mycobacterial and plasmodial enoyl reductases by triclosan are presented. We also describe recent efforts to develop inhibitors of M. tuberculosis and P. falciparum enoyl reductase enzyme activity.

Purine Nucleoside Phosphorylase: A Potential Target for the Development of Drugs to Treat T-Cell- and Apicomplexan Parasite-Mediated Diseases

Purine nucleoside phosphorylase (PNP) catalyzes the reversible phosphorolysis of nucleosides and deoxynucleosides, generating ribose 1-phosphate and the purine base, which is an important step of purine catabolism pathway. The lack of such an activity in humans, owing to a genetic disorder, causes T-cell impairment, and thus drugs that inhibit human PNP activity have the potential of being utilized as modulators of the immunological system to treat leukemia, autoimmune diseases, and rejection in organ transplantation. Besides, the purine salvage pathway is the only possible way for apicomplexan parasites to obtain the building blocks for RNA and DNA synthesis, which makes PNP from these parasites an attractive target for drug development against diseases such as malaria. Hence, a number of research groups have made efforts to elucidate the mechanism of action of PNP based on structural and kinetic studies. It is conceivable that the mechanism may be different for PNPs from diverse sources, and influenced by the oligomeric state of the enzyme in solution. Furthermore, distinct transition state structures can make possible the rational design of specific inhibitors for human and apicomplexan enzymes. Here, we review the current status of these research efforts to elucidate the mechanism of PNP-catalyzed chemical reaction, focusing on the mammalian and Plamodium falciparum enzymes, targets for drug development against, respectively, T-Cell- and Apicomplexan parasites-mediated diseases.

Mycobacterial Shikimate Pathway Enzymes as Targets for Drug Design

The aetiological agent of tuberculosis (TB), Mycobacterium tuberculosis, is responsible for millions of deaths annually. The increasing prevalence of the disease, the emergence of multidrug-resistant strains, and the devastating effect of human immunodeficiency virus co-infection have led to an urgent need for the development of new and more efficient antimycobacterial drugs. Since the shikimate pathway is present and essential in algae, higher plants, bacteria, and fungi, but absent from mammals, the gene products of the common pathway might represent attractive targets for the development of new antimycobacterial agents. In this review we describe studies on shikimate pathway enzymes, including enzyme kinetics and structural data. We have focused on mycobacterial shikimate pathway enzymes as potential targets for the development of new anti-TB agents.

A role for histone-like protein H1 (H-NS) in the regulation of hemolysin expression by Serratia marcescens

The histone-like protein H1 (H-NS) is an abundant structural component of the bacterial nucleoid and influences many cellular processes including recombination, transcription and transposition. Mutations in the hns gene encoding H-NS are highly pleiotropic, affecting the expression of many unrelated genes. We have studied the role of H-NS on the regulation of hemolysin gene expression in Serratia marcescens. The Escherichia coli hns mutant carrying S. marcescens hemolysin genes on a plasmid constructed by ligation of the 3.2-kb HindIII-SacI fragment of pR02 into pBluescriptIIKS, showed a high level of expression of this hemolytic factor. To determine the osmoregulation of wild-type and hns defective mutants the cells were grown to mid-logarithmic phase in LB medium with 0.06 or 0.3 M NaCl containing ampicillin and kanamycin, whereas to analyze the effect of pH on hemolysin expression, the cells were grown to late-logarithmic phase in LB medium buffered with 0.1 M Tris-HCl, pH 4.5 to 8.0. To assay growth phase-related hemolysin production, bacterial cells were grown in LB medium supplemented with ampicillin and kanamycin. The expression of S. marcescens hemolysin genes in wild-type E. coli and in an hns-defective derivative at different pH and during different growth phases indicated that, in the absence of H-NS, the expression of hemolysin did not vary with pH changes or growth phases. Furthermore, the data suggest that H-NS may play an important role in the regulation of hemolysin expression in S. marcescens and its effect may be due to changes in DNA topology influencing transcription and thus the amount of hemolysin expression. Implications for the mechanism by which H-NS influences gene expression are discussed.

Drugs that inhibit mycolic acid biosynthesis in Mycobacterium tuberculosis

Tuberculosis resurged in the late 1980s and now kills more than 2 million people a year. The reemergence of tuberculosis as a potential public health threat, the high susceptibility of human immunodeficiency virus-infected persons to the disease, and the proliferation of multi-drug-resistant (MDR) strains have created much scientific interest in developing new antimycobacterial agents to both treat Mycobacterium tuberculosis strains resistant to existing drugs, and shorten the duration of short-course treatment to improve patient compliance. Bacterial cell-wall biosynthesis is a proven target for new antibacterial drugs. Mycolic acids, which are key components of the mycobacterial cell wall, are alpha-alkyl, beta-hydroxy fatty acids, with a species-dependent saturated "short" arm of 20-26 carbon atoms and a "long" meromycolic acid arm of 50-60 carbon atoms. The latter arm is functionalized at regular intervals by cyclopropyl, alpha-methyl ketone, or alpha-methyl methylethers groups. The mycolic acid biosynthetic pathway has been proposed to involve five distinct stages: (i) synthesis of C20 to C26 straight-chain saturated fatty acids to provide the alpha-alkyl branch; (ii) synthesis of the meromycolic acid chain to provide the main carbon backbone, (iii) modification of this backbone to introduce other functional groups; (iv) the final Claisen-type condensation step followed by reduction; and (v) various mycolyltransferase processes to cellular lipids. The drugs shown to inhibit mycolic acid biosynthesis are isoniazid, ethionamide, isoxyl, thiolactomycin, and triclosan. In addition, pyrazinamide was shown to inhibit fatty acid synthase type I which, in turn, provides precursors for fatty acid elongation to long-chain mycolic acids by fatty acid synthase II. Here we review the biosynthesis of mycolic acids and the mechanism of action of antimicrobial agents that act upon this pathway. In addition, we describe molecular modeling studies on InhA, the bona-fide target for isoniazid, which should improve our understanding of the amino acid residues involved in the enzyme's mechanism of action and, accordingly, provide a rational approach to the design of new drugs.

Comparison of pulsed-field gel electrophoresis and PCR analysis of polymorphisms on the mec hypervariable region for typing methicillin-resistant Staphylococcus aureus

Two hundred fifty-four methicillin-resistant Staphylococcus aureus (MRSA) strains typed by pulsed-field gel electrophoresis (PFGE) were tested by PCR for the mec-associated hypervariable region (HVR-PCR) to determine their number of direct repeat units (DRUs). Eight different groups of repeats were found among the MRSA strains and compared to 28 pulsotypes classified by PFGE. Some MRSA strains belonging to the same pulsotype showed different numbers of DRUs. HVR-PCR was rapid, easy to perform, and reproducible and has the ability to obtain an unambiguous positive result for each isolate analyzed. However, this technique shows a discriminatory power inferior to that of PFGE. We conclude that PFGE is a more reliable method of typing MRSA than HVR-PCR.

Cloning and overexpression in soluble form of functional shikimate kinase and 5-enolpyruvylshikimate 3-phosphate synthase enzymes from Mycobacterium tuberculosis

Tuberculosis (TB) resurged in the late 1980s and an estimated 1.87 million people died of TB in 1997. The reemergence of tuberculosis as a public health threat, the high susceptibility of HIV-infected persons, and the proliferation of multidrug-resistant strains have created a need to develop new antimycobacterial agents. The existence of a shikimate pathway has been predicted by the determination of the genome sequence of Mycobacterium tuberculosis. The M. tuberculosis aroK-encoded shikimate kinase and aroA-encoded 5-enolpyruvylshikimate 3-phosphate (EPSP) synthase were cloned and the enzymes overexpressed in soluble form. Overexpression was achieved without isopropyl beta-d-thiogalactoside induction, and cells grown to stationary phase yielded approximately 30% of target proteins to total soluble cell proteins. Enzyme activity measurements using coupled assays demonstrated that there was a 328-fold increase in specific activity for shikimate kinase and 101-fold increase for EPSP synthase.

Structures of purine nucleoside phosphorylase from Mycobacterium tuberculosis in complexes with immucillin-H and its pieces

A structural genomics comparison of purine nucleoside phosphorylases (PNPs) indicated that the enzyme encoded by Mycobacterium tuberculosis (TB-PNP) resembles the mammalian trimeric structure rather than the bacterial hexameric PNPs. The crystal structure of M. tuberculosis PNP in complex with the transition-state analogue immucillin-H (ImmH) and inorganic phosphate was solved at 1.75 A resolution and confirms the trimeric structure. Binding of the inhibitor occurs independently at the three catalytic sites, unlike mammalian PNPs which demonstrate negative cooperativity in ImmH binding. Reduced subunit interface contacts for TB-PNP, compared to the mammalian enzymes, correlate with the loss of the cooperative inhibitor binding. Mammalian and TB-PNPs both exhibit slow-onset inhibition and picomolar dissociation constants for ImmH. The structure supports a catalytic mechanism of reactant destabilization by neighboring group electrostatic interactions, transition-state stabilization, and leaving group activation. Despite an overall amino acid sequence identity of 33% between bovine and TB-PNPs and almost complete conservation in active site residues, one catalytic site difference suggests a strategy for the design of transition-state analogues with specificity for TB-PNP. The structure of TB-PNP was also solved to 2.0 A with 9-deazahypoxanthine (9dHX), iminoribitol (IR), and PO(4) to reconstruct the ImmH complex with its separate components. One subunit of the trimer has 9dHX, IR, and PO(4) bound, while the remaining two subunits contain only 9dHX. In the filled subunit, 9dHX retains the contacts found in the ImmH complex. However, the region of IR that corresponds to the oxocarbenium ion is translocated in the direction of the reaction coordinate, and the nucleophilic phosphate rotates away from the IR group. Loose packing of the pieces of ImmH in the catalytic site establishes that covalent connectivity in ImmH is required to achieve the tightly bound complex.

Purine nucleoside phosphorylase from Mycobacterium tuberculosis. Analysis of inhibition by a transition-state analogue and dissection by parts

Purine salvage pathways are predicted to be present from the genome sequence of Mycobacterium tuberculosis. The M. tuberculosis deoD gene encodes a presumptive purine nucleoside phosphorylase (PNP). The gene was cloned, expressed, purified, and found to exhibit PNP activity. Purified M. tuberculosis PNP is trimeric, similar to mammalian PNP's but unlike the hexameric Escherichia coli enzyme. Immucillin-H is a rationally designed analogue of the transition state that has been shown to be a potent inhibitor of mammalian PNP's. This inhibitor also exhibits slow-onset inhibition of M. tuberculosis PNP with a rapid, reversible inhibitor binding (K(i) of 2.2 nM) followed by an overall dissociation constant (K(i)) of 28 pM, yielding a K(m)/K(i) value of 10(6). Time-dependent tight binding of the inhibitor occurs with a rate of 0.1 s(-)(1), while relaxation of the complex is slower at 1.4 x 10(-)(3) s(-)(1). The pH dependence of the K(i) value of immucillin-H to the M. tuberculosis PNP suggests that the inhibitor binds as the neutral, unprotonated form that is subsequently protonated to generate the tight-binding species. The M. tuberculosis enzyme demonstrates independent and equivalent binding of immucilin-H at each of the three catalytic sites, unlike mammalian PNP. Analysis of the components of immucillin-H confirms that the inhibition gains most of its binding energy from the 9-deazahypoxanthine group (K(is) of 0.39 microM) while the 1,4-dideoxy-1,4-iminoribitol binds weakly (K(is) of 2.9 mM). Double-inhibition studies demonstrate antagonistic binding of 9-deazahypoxanthine and iminoribitol (beta = 13). However, the covalent attachment of these two components in immucillin-H increases equilibrium binding affinity by a factor of >14 000 (28 pM vs 0.39 microM) compared to 9-deazahypoxanthine alone, and by a factor of >10(8) compared to iminoribitol alone (28 pM vs 2.9 mM), from initial velocity measurements. The structural basis for M. tuberculosis PNP inhibition by immucillin-H and by its component parts is reported in the following paper [Shi, W., Basso, L. A., Santos, D. S., Tyler, P. C., Furneaux, R. H., Blanchard, J. S., Almo, S. C., and Schramm, V. L. (2001) Biochemistry 40, 8204-8215].

Apoptosis of murine peritoneal macrophages induced by an avian pathogenic strain of Escherichia coli

The mechanisms used by avian strains of Escherichia coli to invade the respiratory epithelia, leading to septicemia in poultry, are not well-established. In this work, we show that resident murine peritoneal macrophages infected in vitro with an avian strain of E. coli underwent apoptosis 4 h after infection (55.6% of apoptosis in infected cells versus 3.5% in non-infected cells). Heat-inactivated bacteria did not induce apoptosis and the inhibition of phagocytosis by pretreatment of cells with cytochalasin D reduced the number of apoptotic cells from 55.6 to 13.9% (P<0.05), showing that the bacteria must be intracellularly located and viable to induce apoptosis. Therefore, these data suggest that induction of macrophage apoptosis may be a pathogenic mechanism employed by avian E. coli to circumvent the host defences and invade the respiratory epithelia.

The chromatin-associated protein H-NS alters DNA topology in vitro

H-NS is one of the two most abundant proteins in the bacterial nucleoid and influences the expression of a number of genes. We have studied the interaction of H-NS with DNA; purified H-NS was demonstrated to constrain negative DNA supercoils in vitro. This provides support for the hypothesis that H-NS influences transcription via changes in DNA topology, and is evidence of a structural role for H-NS in bacterial chromatin. The effects of H-NS on topology were only observed at sub-saturating concentrations of the protein. In addition, a preferred binding site on DNA was identified by DNase I footprinting at sub-saturating H-NS concentrations. This site corresponded to a curved sequence element which we previously showed, by in vivo studies, to be a site at which H-NS influences transcription of the proU operon. When present in saturating concentrations, H-NS did not constrain supercoils and bound to DNA in a sequence-independent fashion, covering all DNA molecules from end to end, suggesting that H-NS may form distinct complexes with DNA at different H-NS:DNA ratios. The data presented here provide direct support for the hypothesis that H-NS acts at specific sites to influence DNA topology and, hence, transcription.

The chromatin-associated protein H-NS interacts with curved DNA to influence DNA topology and gene expression

H-NS is an abundant structural component of bacterial chromatin and influences many cellular processes, including recombination, transposition, and transcription. We have studied the mechanism of action of H-NS at the osmotically regulated proU promoter. The interaction of H-NS with a curved DNA element located downstream of the proU promoter is required for normal regulation of expression. Heterologous curved sequences can replace the regulatory role of the proU curve. Hence, the luxAB and lacZ reporter genes, which differ in the presence or absence of a curve, can indicate very different patterns of transcription. H-NS interacts preferentially with these curved DNA elements in vitro. Furthermore, in vivo the interaction of H-NS with curved DNA participates in the control of plasmid linking number. The data suggest that H-NS-dependent changes in DNA topology play a role in the osmoregulation of proU expression.

Expression and mutational analysis of the nucleoid-associated protein H-NS of Salmonella typhimurium

The H-NS (H1) protein is a major component of bacterial chromatin. Mutations in the hns (osmZ) gene encoding H-NS are highly pleiotropic, affecting the expression of many unrelated genes in an allele-specific manner. H-NS expression was found not to vary with growth phase or growth medium osmolarity. Additionally, 10 independent hns mutations were isolated and characterized. Five of these mutations were the result of an IS10 insertion, each generating a truncated polypeptide. The other five mutations were the same specific deletion of one amino acid, delta Ala46. The various hns mutations exhibited different phenotypes and influenced DNA topology to variable extents. Implications for the mechanism by which H-NS influences gene expression are discussed.

Virulence factors of avian Escherichia coli

A total of 45 strains of Escherichia coli isolates from chickens with colisepticemia were examined for virulence factors commonly found in pathogenic groups of E. coli. These strains were studied for the following: pathogenicity in 1-day-old chicks; toxin, hemolysin, and colicin production; cell invasiveness and adherence; hemagglutination for fimbriae detection; serum resistance; aerobactin production in iron-limited conditions; and plasmid content. The characteristics exhibited by virulent strains were invasion for HeLa and chicken fibroblast cells, serum resistance, colicin V, and aerobactin production. None of the isolates were toxigenic or positive in hemagglutination tests. The molecular genetic studies of the virulence factors by agarose electrophoresis showed that the plasmids of these strains are of high molecular weight.

Characterization of plasmids in a sucrose-fermenting strain of Escherichia coli

A multiply drug-resistant strain of Escherichia coli isolated from a patient in Bangladesh was shown to carry four types of plasmids based on size differences. One type carries a gene or genes for sucrose fermentation.

Partial purification and characterization of a heat-labile enterotoxin of Escherichia coli

A partially purified enterotoxin was obtained from the growth medium of Escherichia coli strain 711 (P307), a derivative of E. coli K-12, by ultrafiltration, precipitation with ammonium sulfate, molecular sieving, and anion exchange column chromatography. The active moiety, which is heat-labile, behaved like a protein particle of 180,000 to 200,000 daltons during molecular sieving and ultracentrifugation. During polyacrylamide gel electrophoresis in sodium dodecyl sulfate (SDS-PAGE), it dissociated into two subunits with apparent molecular weights of 68,000 to 70,000 and 14,000 to 15,000. SDS-PAGE after heating in SDS changed the larger subunit to an apparent molecular weight of about 40,000; the smaller subunit did not change. The intact particle induced rounding of the cells in Y-1 mouse adrenal tumor cells used for assay. The detergent-dissociated molecules were not active. Proteolysis of the purified toxin by tolylsulfonyl phenylalanyl chloromethyl ketone-trypsin appeared to enhance its activity. The addition of serum to the assay medium resulted in partial depression of the activity. Activity was also abolished by preincubation of the toxin with either a rabbit antiserum to it or solutions containing GM1 ganglioside. The length of time needed to evoke a response in the assay system by fractions from different stages in the purification of the enterotoxin was a useful parameter in the evaluation of specific activity.

Diagnosis of Wuchereria bancrofti filariasis by immunofluorescence using microfilariae as antigen

A new technique for the diagnosis of wuchereriasis is described. Microfilariae treated with proteolytic enzyme were used as antigen for the immunofluorescent reaction. The specificity of the reaction is demonstrated in sera from persons who have a microfilariaemia, individuals with clinical symptoms of the disease but no microfilariaemia, those who have no clinical symptoms, but harbour other parasites, and in persons living in France, where the Wuchereria bancrofti filariasis is absent.

Genetic and physical characteristics of an enterotoxin plasmid

We are engaged in the genetic and physical characterization of an enterotoxin (Ent) plasmid, Ent P307, which contains genes for the production of a hear-labile and a heat-stable enterotoxin. We are using an Escherichia coli K-12 strain, 711 (P307), constructed by S. Falkow, which contains no other plasmids besides Ent P307. Our genetic studies have shown that the plasmid is incompatible with the sex factor F, both in the integrated (Hfr) and the autonomous (F-prime) state. Ent P307 can thus be assigned to incompatibility group FI. An R factor, R386, which belongs to the same incompatibility group, was also found to be incompatibile with Ent P307, whereas five other R factors belonging to different incompatibility groups were compatible with Ent P307. In the presence of Ent P307, conjugal transfer and sensitivity to a male-specific phage of a derepressed F-like R factor, R1drd19, were repressed. Ent P307 is, thus, finO+. Presumably, it also causes repression of its own transfer genes since conjugal transfer of Ent P307 could not be demonstrated. Unlike F, it does not restrict the growth of female-specific phage phiII. From physical studies on extracted deoxyribonucleic acid, the molecular weight of Ent P307 was determined to be 54 X 10(6). By electron microscope heteroduplex analysis, the plasmid was found to be homologous with F in four regions, encompassing about half of its length. One long region and two short ones contain genes for conjugal transfer; the other short region carries genes for replication and incompatibility.

New arteriographic and surgical techniques for vertebral arteriopathies

Vertebral arterial insufficiency syndromes are being diagnosed with greater frequency, and would appear to be at least as common as carotid disease in causing cerebrovascular insufficiency. Carotid lesions are nearly always arteriosclerotic, but vertebral obstructions are caused at least as frequently by nonarteriosclerotic lesions, including tortuosity with kink and external bands, slings, bony compression, and congenital aberrations.

A method of cerebral arteriography has been standardized and a new radiographic sign of comparative opacification times of the intracranial carotid and basilar arteries has been tested as a pathognomonic sign of vertebral-basilar arterial insufficiency.

The concept of the innominate-subclavian-vertebral complex as a single surgical geometric unit has allowed the development of a graded surgical approach of arteriolysis, endarterectomy, and resection and anastomosis in managing 97% of obstructive vertebral arteriopathies.

A new surgical operation of distal subclavian resection and anastomosis to correct vertebral and/or subclavian arterial tortuosity with kinking has proven helpful in ablating symptoms of vertebral-basilar arterial insufficiency.