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Mannose-Specific Plant Lectins from the Amaryllidaceae Family Qualify as Efficient Microbicides for Prevention of Human Immunodeficiency Virus Infection. Jan Balzarini, 2004.The plant lectins derived from Galanthus nivalis (Snowdrop) (GNA) and Hippeastrum hybrid (Amaryllis) (HHA) selectively inhibited a wide variety of human immunodeficiency virus type 1 (HIV-1) and HIV-2 strains and clinical (CXCR4- and CCR5-using) isolates in different cell types . They also efficiently inhibited infection of T lymphocytes by a variety of mutant virus strains . GNA and HHA markedly prevented syncytium formation between persistently infected HUT-78/HIV cells and uninfected T lymphocytes . The plant lectins did not measurably affect the antiviral activity of other clinically approved anti-HIV drugs used in the clinic when combined with these drugs . Short exposure of the lectins to cell-free virus particles or persistently HIV-infected HUT-78 cells markedly decreased HIV infectivity and increased the protective (microbicidal) activity of the plant lectins . Flow cytometric analysis and monoclonal antibody binding studies and a PCR-based assay revealed that GNA and HHA do not interfere with CD4, CXCR4, CCR5, and DC-SIGN and do not specifically bind with the membrane of uninfected cells . Instead, GNA and HHA likely interrupt the virus entry process by interfering with the virus envelope glycoprotein . HHA and GNA are odorless, colorless, and tasteless, and they are not cytotoxic, antimetabolically active, or mitogenic to human primary T lymphocytes at concentrations that exceed their antivirally active concentrations by 2 to 3 orders of magnitude . GNA and HHA proved stable at high temperature (50°C) and low pH (5.0) for prolonged time periods and can be easily formulated in gel preparations for microbicidal use; they did not agglutinate human erythrocytes and were not toxic to mice when administered intravenously . Antiplasmodial Chalcones Inhibit Sorbitol-Induced Hemolysis of Plasmodium falciparum-Infected Erythrocytes. Mei-Lin Go, 2004.A series of alkoxylated and hydroxylated chalcones previously reported to have antiplasmodial activities in vitro were investigated for their effects on the new permeation pathways induced by the malaria parasite in the host erythrocyte membrane . Of 21 compounds with good antiplasmodial activities (50% inhibitory concentrations [IC50s],  20 µM), 8 members were found to inhibit sorbitol-induced lysis of parasitized erythrocytes to a significant extent (40% of control values) at a concentration (10 µM) that was close to their antiplasmodial IC50s . Qualitative structure-activity analysis suggested that activity was governed to a greater extent by a substitution on ring B than on ring A of the chalcone template . Most of the active compounds had methoxy or dimethoxy groups on ring B . Considerable variety was permitted on ring A in terms of the electron-donating or -withdrawing property . Lipophilicity did not appear to be an important determinant for activity . Although they are not exceptionally potent as inhibitors (lowest IC50, 1.9 µM), the chalcones compare favorably with other more potent inhibitors in terms of their selective toxicities against plasmodia and their neutral character .
Assembly of Colicin A in the Outer Membrane of Producing Escherichia coli Cells Requires both Phospholipase A and One Porin, but Phospholipase A Is Sufficient for Secretion. Daniele Cavard, 2002.Three oligomeric forms of colicin A with apparent molecular masses of about 95 to 98 kDa were detected on sodium dodecyl sulfate (SDS)-polyacrylamide gels loaded with unheated samples from colicin A-producing cells of Escherichia coli . These heat-labile forms, called colicins Au, were visualized both on immunoblots probed with monoclonal antibodies against colicin A and by radiolabeling . Cell fractionation studies show that these forms of colicin A were localized in the outer membrane whether or not the producing cells contained the cal gene, which encodes the colicin A lysis protein responsible for colicin A release in the medium . Pulse-chase experiments indicated that their assembly into the outer membrane, as measured by their heat modifiable migration in SDS gels, was an efficient process . Colicins Au were produced in various null mutant strains, each devoid of one major outer membrane protein, except in a mutant devoid of both OmpC and OmpF porins . In cells devoid of outer membrane phospholipase A (OMPLA), colicin A was not expressed . Colicins Au were detected on immunoblots of induced cells probed with either polyclonal antibodies to OmpF or monoclonal antibodies to OMPLA, indicating that they were associated with both OmpF and OMPLA . Similar heat-labile forms were obtained with various colicin A derivatives, demonstrating that the C-terminal domain of colicin A, but not the hydrophobic hairpin present in this domain, was involved in their formation . Functional Analysis of the Bacillus subtilis Zur Regulon. Ahmed Gaballa, 2002.The Bacillus subtilis zinc uptake repressor (Zur) regulates genes involved in zinc uptake . We have used DNA microarrays to identify genes that are derepressed in a zur mutant . In addition to members of the two previously identified Zur-regulated operons (yciC and ycdHI-yceA), we identified two other genes, yciA and yciB, as targets of Zur regulation . Electrophoretic mobility shift experiments demonstrated that all three operons are direct targets of Zur regulation . Zur binds to an  28-bp operator upstream of the yciA gene, as judged by DNase I footprinting, and similar operator sites are found preceding each of the previously described target operons, yciC and ycdHI-yceA . Analysis of a yciA-lacZ fusion indicates that this operon is induced under zinc starvation conditions and derepressed in the zur mutant . Phenotypic analyses suggest that the YciA, YciB, and YciC proteins may function as part of the same Zn(II) transport pathway . Mutation of yciA or yciC, singly or in combination, had little effect on growth of the wild-type strain but significantly impaired the growth of the ycdH mutant under conditions of zinc limitation . Since the YciA, YciB, and YciC proteins are not obviously related to any known transporter family, they may define a new class of metal ion uptake system . Mutant strains lacking all three identified zinc uptake systems (yciABC, ycdHI-yceA, and zosA) are dependent on micromolar levels of added zinc for optimal growth .
Stable Carbon Isotope Fractionation by Sulfate-Reducing Bacteria. Kathleen L. Londry, 2003.Biogeochemical transformations occurring in the anoxic zones of stratified sedimentary microbial communities can profoundly influence the isotopic and organic signatures preserved in the fossil record . Accordingly, we have determined carbon isotope discrimination that is associated with both heterotrophic and lithotrophic growth of pure cultures of sulfate-reducing bacteria (SRB) . For heterotrophic-growth experiments, substrate consumption was monitored to completion . Sealed vessels containing SRB cultures were harvested at different time intervals, and  13C values were determined for gaseous CO2, organic substrates, and products such as biomass . For three of the four SRB, carbon isotope effects between the substrates, acetate or lactate and CO2, and the cell biomass were small, ranging from 0 to 2 . However, for Desulfotomaculum acetoxidans, the carbon incorporated into biomass was isotopically heavier than the available substrates by 8 to 9 . SRB grown lithoautotrophically consumed less than 3% of the available CO2 and exhibited substantial discrimination (calculated as isotope fractionation factors [ ]), as follows: for Desulfobacterium autotrophicum,
values ranged from 1.0100 to 1.0123; for Desulfobacter hydrogenophilus, the
value was 0.0138, and for Desulfotomaculum acetoxidans, the
value was 1.0310 . Mixotrophic growth of Desulfovibrio desulfuricans on acetate and CO2 resulted in biomass with a
13C composition intermediate to that of the substrates . The extent of fractionation depended on which enzymatic pathways were used, the direction in which the pathways operated, and the growth rate, but fractionation was not dependent on the growth phase . To the extent that environmental conditions affect the availability of organic substrates (e.g., acetate) and reducing power (e.g., H2), ecological forces can also influence carbon isotope discrimination by SRB .
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