Crystal structure and dimerization equilibria of PcoC, a methionine-rich copper resistance protein from Escherichia coli

PcoC is a soluble periplasmic protein encoded by the plasmid-born pco copper resistance operon of Escherichia coli. Like PcoA, a multicopper oxidase encoded in the same locus and its chromosomal homolog CueO, PcoC contains unusual methionine rich sequences. Although essential for copper resistance, the functions of PcoC, PcoA, and their conserved methionine-rich sequences are not known. Similar methionine motifs observed in eukaryotic copper transporters have been proposed to bind copper, but there are no precedents for such metal binding sites in structurally characterized proteins. The high-resolution structures of apo PcoC, determined for both the native and selenomethionine-containing proteins, reveal a seven-stranded beta barrel with the methionines unexpectedly housed on a solvent-exposed loop. Several potential metal-binding sites can be discerned by comparing the structures to spectroscopic data reported for copper-loaded PcoC. In the native structure, the methionine loop interacts with the same loop on a second molecule in the asymmetric unit. In the selenomethionine structure, the methionine loops are more exposed, forming hydrophobic patches on the protein surface. These two arrangements suggest that the methionine motifs might function in protein-protein interactions between PcoC molecules or with other methionine-rich proteins such as PcoA. Analytical ultracentrifugation data indicate that a weak monomer-dimer equilibrium exists in solution for the apo protein. Dimerization is significantly enhanced upon binding Cu(I) with a measured delta(deltaG degrees )相似文献   

In Vitro and in Vivo Phlebovirus Inhibition by Nucleosides Related to Ribavirin

Abstract

Eleven compounds were compared to ribavirin for their in vitro and in vivo inhibition of Punta Toro virus (PTV), a phlebovirus in the Bunyaviridae virus family.     

Single and multiple worm infections of Echinostoma caproni (Trematoda) in the golden hamster

Six of 10 hamsters fed a single metacercarial cyst of Echinostoma caproni (single-worm infections) and 13 of 19 hamsters fed either 2 or 5 cysts (multiple-worm infections) were infected with adult echinostomes at necropsy 22 days post-infection. Considerable histopathological changes to the small intestine occurred in hamsters carrying single-worm infections. There were no differences in either mean length, width or wet weight of echinostomes in single- versus multiple-worm infections. The mean number of eggs/worm from single-worm infections (525) was significantly greater than that from multiple-worm infections (288). The average percentage of fully developed miracidia/worm from single worms (94%) was similar to that from worms in multiple infections (92-95%). Single worms of E. caproni were capable of self-fertilization and production of viable eggs. Miracidia derived from single worms were as capable of infecting laboratory-reared Biomphalaria glabrata and producing patent rediae as were those from multiple infections.     

Factors associated with neonatal lamb mortality

Three factors were associated with lamb neonatal mortality: birthweight (P<0.003), number of lambs born per ewe (P<0.001) and lamb sex (P<0.32). Lamb birthweight had the greatest predictive power for survival during the neonatal period. The neonatal mortality rate was 14.3%. The age specific mortality for lambs one day old was 7.9% (P<0.05). Seventy-nine percent of the lambs that died, did so by the end of the fourth post-natal day. Starvation was associated with 58.3% (P < 0.05) of the lamb deaths.     

Seasonal trends in intestinal nematode infection and medicinal plant use among chimpanzees in the Mahale Mountains, Tanzania

A longitudinal study of nematode infection in chimpanzees was conducted between 1989 and 1994 on the M group chimpanzees of the Mahale Mountains National Park, Tanzania during two annual dry and rainy season periods and a third rainy season. Chemical and physical antiparasite properties of medicinal plant use against the strongyle nematodeOesophagostomum stephanostomum have recently been reported at Mahale. Here, the incidence of nematode infections were analyzed for seasonal trends to elucidate the possible influence of parasite infection on previously reported seasonality of medicinal plant use and to test the hypothesis that the use of these plants is stimulated byO. stephanostomum. The number of chimpanzees infected byO. stephanostomum was significantly higher in the rainy season than in the dry season of both 1989–1990 and 1991–1992. However, the incidence ofTrichuris trichura andStrongyloides fuelleborni showed no seasonality. Reinfection of individuals byO. stephanostomum occurred in synchrony with annual variation in rainfall: there was a sharp rise in the occurrence of new infections per individual within one to two months after the beginning of the first heavy rains of the season. This pattern coincides with the reproductive cycle of this nematode species.O. stephanostomum (95%) infections were associated significantly more frequently with medicinal plant use than eitherT. trichiura (50%) orS. fuelleborni (40%) infections. These observations are consistent with previous reports for the increased use of these plants during the rainy season and are consistent the hypothesis that medicinal plant use is stimulated byO. stephanostomum infection.     

Experimental infections of waterfowl with Sphaeridiotrema globulus (Digenea)

Sphaeridiotrema globulus in experimentally infected mute swans (Cygnus olor), mallard ducks (Anas platyrhynchos) and Canada geese (Branta canadensis) induced ulcerative hemorrhagic enteritis. Sites of infection include the jejunum and ileum. The digeneans ulcerated the intestine. The inflammatory response was primarily lymphocytic with some eosinophils. Severe hemorrhage from damaged submucosal capillaries provided a blood meal for the parasite and caused anemia in the host. Extra-medullary hematopoiesis occurred in the liver, and an erythroid hyperplasia occurred in the bone marrow of infected birds. Infected birds exhibited muscular weakness and died from shock associated with severe blood loss. Mallards and Canada geese were less susceptible to fatal infection than the mute swan as evidenced by survivors in the higher dose groups.     

Use of Disposable Micro Tissue Culture Plates for Antiviral and Interferon Induction Studies

A reproducible test system requiring small amounts of test compound was developed for evaluating antiviral and interferon-inducing activity. In the antiviral experiments, KB cells were grown in disposable polystyrene microplates covered with a standard domestic plastic wrap. Viruses used in the system were types 1 and 2 herpes simplex virus, vaccinia virus, type 3 adenovirus, myxoma virus, pseudorabies virus, type 3 parainfluenza virus, types 1A and 13 rhinovirus, vesicular stomatitis virus, coxsackievirus B, and type 2 poliovirus. Inhibition of viral cytopathogenic effect was the primary criterion of evaluation of antiviral activity. Reduction in cell and supernatant fluid virus titers was used as a secondary means of evaluation. The microplate system was adaptable for determining prophylactic, therapeutic, and inactivating effects against viruses. Mouse L-929 cells were used for the interferon induction studies, with vesicular stomatitis virus utilized as the indicator of interferon activity. Known active compounds evaluated in this microplate system had activity similar to that seen in macro in vitro systems.