Structure-activity relationships of 3-aminoquinazolinediones, a new class of bacterial type-2 topoisomerase (DNA gyrase and topo IV) inhibitors

A series of 3-aminoquinazolinediones was synthesized and evaluated for its antibacterial and DNA gyrase activity. The SAR around the quinazolinedione core was explored and the optimal substitutions were combined to give two compounds, 2r and 2s, with exceptional enzyme potency (IC50 = 0.2 microM) and activity against gram-positive organisms (MIC's = 0.015-0.06 microg/mL).     

Lead removal through biological sulfate reduction process

The feasibility of lead removal through biological sulfate reduction process with ethanol as electron donor was investigated. Sulfide-rich effluent from biological process was used to remove lead as lead sulfide precipitate. The experiments were divided into two stages; Stage I startup and operation of sulfidogenic process in a UASB reactor and Stage II lead sulfide precipitation. In Stage I, the COD:S ratio was gradually reduced from 15:1 to 2:1. At the COD:S ratio of 2:1, sulfidogenic condition was achieved as identified by 80-85% of electron flow by sulfate reducing bacteria (SRB). COD and sulfate removal efficiency were approximately 78% and 50%, respectively. In Stage II, the effluent from UASB reactor containing sulfide in the range of 30-50 mg/L and lead-containing solution of 45-50 mg/L were fed continuously into the precipitation chamber in which the optimum pH for lead sulfide precipitation of 7.5-8.5 was maintained. It was found that lead removal of 85-95% was attained.     

Identification of leishmania fructose-1,6-bisphosphate aldolase as a novel activator of host macrophage Src homology 2 domain containing protein tyrosine phosphatase SHP-1

The macrophage protein tyrosine phosphatase-1 SHP-1 has been implicated in the pathogenesis of infection with leishmania. To identify the factors that may interact with SHP-1, Leishmania donovani promastigote lysates were added to a GST-SHP-1 affinity matrix. A 44 kDa specifically bound protein was identified as leishmania fructose-1,6-bisphosphate aldolase (aldolase). Purified leishmania aldolase bound to SHP-1 indicating that the interaction was direct. In contrast, purified mammalian aldolase did not bind to SHP-1. Consistent with this, leishmania aldolase activated SHP-1 in vitro, whereas mammalian aldolase did not. The presence of leishmania aldolase in the cytosolic fractions prepared from infected macrophages indicated that leishmania aldolase is exported from phagolysosomes in infected cells where it can target host cytosolic proteins. In fact, co-immunoprecipitation showed association of leishmania aldolase with SHP-1. Moreover, leishmania aldolase-expressing macrophages showed the deactivated phenotype of leishmania infected cells as judged by much reduced inability to induce expression of nitric-oxide synthase in response to interferon-γ treatment. Collectively, these data show that leishmania aldolase is a novel SHP-1 binding and activating protein that contributes to macrophage dysfunction.     

Characterization of the heterodimeric MegBIIa:MegBIIb aldo-keto reductase involved in the biosynthesis of L-mycarose from Micromonospora megalomicea

Two putative C3-ketoreductases, MegBIIa and MegBIIb (formerly MegBII and MegDVII, respectively), homologues to members of the family 12 of aldo-keto reductase (AKR12) superfamily of enzymes, were identified in the megalomicin gene cluster from Micromonospora megalomicea. Proteins from this family are involved in the metabolism of TDP-sugars by actinomycetes. MegBIIa was originally proposed to be involved in the l-mycarose biosynthetic pathway, while MegBIIb in the l-megosamine biosynthetic pathway. In this work we have investigated the role of these proteins in the biosynthesis of dTDP-l-mycarose. In vivo analysis of the dTDP-sugar intermediates indicated that neither MegBIIa nor its homologue, MegBIIb, was a fully active enzyme by itself. Surprisingly, C3-ketoreductase activity was observed only in the presence of both MegBIIa and MegBIIb, suggesting the formation of an active complex. Copurification and size exclusion chromatography experiments confirmed that MegBIIa and MegBIIb interact forming a 1:1 heterodimeric complex. Finally, a mycarose operon containing megBIIa and megBIIb together with the other biosynthetic genes of the l-mycarose pathway was constructed and tested by bioconversion experiments in Escherichia coli. High levels of mycarosyl-erythronolide B were produced under the condition tested, confirming the role of these two proteins in this metabolic pathway.     

A novel function for the N-terminal nucleophile hydrolase fold demonstrated by the structure of an archaeal inosine monophosphate cyclohydrolase

Inosine 5'-monophosphate (IMP) cyclohydrolase catalyzes the cyclization of 5-formaminoimidazole-4-carboxamide ribonucleotide (FAICAR) to IMP in the final step of de novo purine biosynthesis. Two major types of this enzyme have been discovered to date: PurH in Bacteria and Eukarya and PurO in Archaea. The structure of the MTH1020 gene product from Methanothermobacter thermoautotrophicus was previously solved without functional annotation but shows high amino acid sequence similarity to other PurOs. We determined the crystal structure of the MTH1020 gene product in complex with either IMP or 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) at 2.0 and 2.6 A resolution, respectively. On the basis of the sequence analysis, ligand-bound structures, and biochemical data, MTH1020 is confirmed as an archaeal IMP cyclohydrolase, thus designated as MthPurO. MthPurO has a four-layered alphabeta betaalpha core structure, showing an N-terminal nucleophile (NTN) hydrolase fold. The active site is located at the deep pocket between two central beta-sheets and contains residues strictly conserved within PurOs. Comparisons of the two types of IMP cyclohydrolase, PurO and PurH, revealed that there are no similarities in sequence, structure, or the active site architecture, suggesting that they are evolutionarily not related to each other. The MjR31K mutant of PurO from Methanocaldococcus jannaschii showed 76% decreased activity and the MjE102Q mutation completely abolished enzymatic activity, suggesting that these highly conserved residues play critical roles in catalysis. Interestingly, green fluorescent protein (GFP), which has no structural homology to either PurO or PurH but catalyzes a similar intramolecular cyclohydrolase reaction required for chromophore maturation, utilizes Arg96 and Glu222 in a mechanism analogous to that of PurO.     

Antibiotic Resistance in Food-Borne Bacterial Contaminants in Vietnam

This study was conducted to examine the rate of contamination and the molecular characteristics of enteric bacteria isolated from a selection of food sources in Vietnam. One hundred eighty raw food samples were tested; 60.8% of meat samples and 18.0% of shellfish samples were contaminated with Salmonella spp., and more than 90% of all food sources contained Escherichia coli. The isolates were screened for antibiotic resistance against 15 antibiotics, and 50.5% of Salmonella isolates and 83.8% of E. coli isolates were resistant to at least one antibiotic. Isolates were examined for the presence of mobile genetic elements conferring antibiotic resistance. Fifty-seven percent of E. coli and 13% of Salmonella isolates were found to contain integrons, and some isolates contained two integrons. Sequencing results revealed that the integrons harbored various gene cassettes, including aadA1, aadA2, and aadA5 (resistance to streptomycin and spectinomycin), aacA4 (resistance to aminoglycosides), the dihydrofolate reductase gene cassettes dhfrXII, dfrA1, and dhfrA17 (trimethoprim resistance), the beta-lactamase gene bla_PSE1 (ampicillin resistance), and catB3 (chloramphenicol resistance). Plasmids were also detected in all 23 antibiotic-resistant Salmonella isolates and in 33 E. coli isolates. Thirty-five percent of the Salmonella isolates and 76% of the E. coli isolates contained plasmids of more than 95 kb, and some of the isolates contained two large plasmids. Conjugation experiments showed the successful transfer of all or part of the antibiotic resistance phenotypes among the Salmonella and E. coli food isolates. Our results show that enteric bacteria in raw food samples from Vietnam contain a pool of mobile genetic elements and that the transfer of antibiotic resistance can readily occur between similar bacteria.     

The DEAD-box protein Dbp5 controls mRNA export by triggering specific RNA:protein remodeling events

Messenger RNA (mRNA) export involves the unidirectional passage of ribonucleoprotein particles (RNPs) through nuclear pore complexes (NPCs), presumably driven by the ATP-dependent activity of the DEAD-box protein Dbp5. Here we report that Dbp5 functions as an RNP remodeling protein to displace the RNA-binding protein Nab2 from RNA. Strikingly, the ADP-bound form of Dbp5 and not ATP hydrolysis is required for RNP remodeling. In vivo studies with nab2 and dbp5 mutants show that a Nab2-bound mRNP is a physiological Dbp5 target. We propose that Dbp5 functions as a nucleotide-dependent switch to control mRNA export efficiency and release the mRNP from the NPC.     

An appraisal of Ulva (Ulvophyceae,Chlorophyta) taxonomy

Journal of Applied Phycology - The green seaweed Ulva is important from ecological and economic perspectives, but the identification of species is often problematic. Here we assessed and discussed...     

Effects of ultraviolet light and methyl salicylate on some phenological and agronomic and morphological characteristics of common bean (Phaseolus vulgaris L.)

Journal of Plant Biochemistry and Biotechnology - The aim of this investigation was to study the effect of physical (ultraviolet light) and chemical mutagen (methyl salicylate) on common bean...