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71.
72.
In Bradyrhizobium japonicum, iron uptake from ferric siderophores involves selective outer membrane proteins and non-selective periplasmic and cytoplasmic membrane components that accommodate numerous structurally diverse siderophores. Free iron traverses the cytoplasmic membrane through the ferrous (Fe2+) transporter system FeoAB, but the other non-selective components have not been described. Here, we identify fsrB as an iron-regulated gene required for growth on iron chelates of catecholate- and hydroxymate-type siderophores, but not on inorganic iron. Utilization of the non-physiological iron chelator EDDHA as an iron source was also dependent on fsrB. Uptake activities of 55Fe3+ bound to ferrioxamine B, ferrichrome or enterobactin were severely diminished in the fsrB mutant compared with the wild type. Growth of the fsrB or feoB strains on ferrichrome were rescued with plasmid-borne E. coli fhuCDB ferrichrome transport genes, suggesting that FsrB activity occurs in the periplasm rather than the cytoplasm. Whole cells of an fsrB mutant are defective in ferric reductase activity. Both whole cells and spheroplasts catalyzed the demetallation of ferric siderophores that were defective in an fsrB mutant. Collectively, the data support a model whereby FsrB is required for reduction of iron and its dissociation from the siderophore in the periplasm, followed by transport of the ferrous ion into the cytoplasm by FeoAB. 相似文献
73.
74.
Dietrich P. Steinhuebel Peter Fuhrmann Stephen J. Lippard 《Inorganica chimica acta》1998,270(1-2):527-536
A series of zirconium(IV) complexes, [ZrX2(XDK)], where XDK is the constrained carboxylate ligand m-xylylenediamine bis(Kemp's triacid imide), were prepared and structurally characterized. The solid state structure of the mononuclear carboxylate alkyl complex [Zr(CH2Ph)2(XDK)] reveals that one benzyl group is bonded in an η2-fashion to the metal center. The reactivity of [Zr(CH2Ph)2(XDK)] displays its electrophilic character toward nucleophiles strong enough to displace the η2-benzyl group. Thus, weak sigma donor ligands such as CO, alkynes and anilines do not react, whereas strong sigma donors, such as pyridines and isocyanides, rapidly form the monoadduct [Zr(CH2Ph)2(4-tert-butylpyridine)(XDK)] and [Zr{η2-2,6-Me2PhNCCH2Ph}2(XDK)], an η2-iminoacyl derivative, respectively. Attempts to prepare zirconium amido complexes with H2XDK generally afforded the eight-coordinate [Zr(XDK)2] complex but use of the small amido ligand precursorZr(NMe2)4 allowed [Zr(NMe2)2(4-tert-butylpyridine)(XDK)] to be isolated in good yield. 相似文献
75.
Ruihu Wang 《Inorganica chimica acta》2005,358(3):545-554
The reactions of 4-aminobenzoic acid (4-abaH), 4,4′-bipyridine (4,4′-bipy) and transitional metal ions (ZnII, MnII and CuII) gave rise to four supramolecular architectures, namely, [(4-abaH)2(4,4′-bipy)] (1), {[Zn2(4,4′-bipy)2(4-aba)4] (H2O)5}n (2), {[Mn(4,4′-bipy)2(H2O)4] (4-aba)Br(H2O)3} (3) and {[Cu2(4,4′-bipy)3(H2O)2(4-aba)2](NO3)2(H2O)4}n (4). Their crystal structures were determined by X-ray diffraction and show different structural motifs. 1 is a one-dimensional hydrogen bonding ladder constructed by 4-abaH and 4,4′-bipy. In 2, 4,4′-bipy bridges Zn(4-aba)2 units forming a one-dimensional zigzag chain, which is extended into a three-dimensional framework by crystalline water molecules through hydrogen bonding interactions. Three-dimensional network of 3 is constructed by mononuclear [Mn(4,4′-bipy)2(H2O)4]2+ cations, neutral crystalline water molecules, and 4-aba and Br− anions through extensive hydrogen bonding and π-π interactions. However, one-dimensional ladder formed by 4,4′-bipy and Cu(4-aba) units in 4 is extended into a three-dimensional architecture through interpenetration of the lateral 4-aba arms into squares of the adjacent Cu-(4,4′-bipy) ladders and extensive hydrogen bonding interactions. 相似文献
76.
Srikrishna G Brive L Freeze HH 《Biochemical and biophysical research communications》2005,332(4):1020-1027
We previously reported that N-glycans from bovine lung contain novel carboxylate groups. Here, we provide evidence that the carboxylated glycans contain glutamic acid. We labeled HeLa cells with [2,3-(3)H]glutamate and used a carboxylate-specific monoclonal antibody to enrich for the desired proteins. PNGaseF digestion of these proteins released labeled N-glycans with a free amino group and 1-3 carboxylates. Mild acid hydrolysis had no effect, but strong acid hydrolysis of the glycans released >80% of the (3)H as glutamate. Reducing the carboxylates to alcohols prior to hydrolysis eliminated the [(3)H]glutamate and generated [(3)H]4-amino 5-hydroxy pentanoic acid, suggesting that [(3)H]glutamate was linked to the glycan through its gamma-carboxyl. The glutamate-containing N-glycans resisted exoglycosidase digestion and oligosaccharide processing inhibitors greatly reduced [(3)H]glutamate incorporation. These results demonstrate that mammalian cells synthesize complex-type N-glycans with glutamate linked to their antennae, further expanding their potential for covalent or ionic interactions. 相似文献
77.
J.?L.?You L.?X.?Cao G.?F.?Liu S.?N.?ZhouEmail author H.?M.?Tan Y.?C.?Lin 《World journal of microbiology & biotechnology》2005,21(5):679-682
Summary A total of 94 actinomycete strains were isolated from the marine sediments of a shrimp farm, 87.2% belonged to the genus Streptomyces, others were Micromonospora spp. Fifty-one percent of the actinomycete strains showed activity against the pathogenic Vibrio spp. strains. Thirty-eight percent of marine Streptomyces strains produced siderophores on chrome azurol S (CAS) agar plates. Seven strains of Streptomyces were found to produce siderophores and to inhibit the growth of Vibrio spp. in vitro. Two of them belonged to the Cinerogriseus group, the most frequently isolated group of Streptomyces. The results showed that streptomycetes could be a promising source for biocontrol agents in aquaculture. 相似文献
78.
Ghysels B Ochsner U Möllman U Heinisch L Vasil M Cornelis P Matthijs S 《FEMS microbiology letters》2005,246(2):167-174
Actively secreted iron chelating agents termed siderophores play an important role in the virulence and rhizosphere competence of fluorescent pseudomonads, including Pseudomonas aeruginosa which secretes a high affinity siderophore, pyoverdine, and the low affinity siderophore, pyochelin. Uptake of the iron-siderophore complexes is an active process that requires specific outer membrane located receptors, which are dependent of the inner membrane-associated protein TonB and two other inner membrane proteins, ExbB and ExbC. P. aeruginosa is also capable of using a remarkable variety of heterologous siderophores as sources of iron, apparently by expressing their cognate receptors. Illustrative of this feature are the 32 (of which 28 putative) siderophore receptor genes observed in the P. aeruginosa PAO1 genome. However, except for a few (pyoverdine, pyochelin, enterobactin), the vast majority of P. aeruginosa siderophore receptor genes still remain to be characterized. Ten synthetic iron chelators of catecholate type stimulated growth of a pyoverdine/pyochelin deficient P. aeruginosa PAO1 mutant under condition of severe iron limitation. Null mutants of the 32 putative TonB-dependent siderophore receptor encoding genes engineered in the same genetic background were screened for obvious deficiencies in uptake of the synthetic siderophores, but none showed decreased growth stimulation in the presence of the different siderophores. However, a double knock-out mutant of ferrienterobactin receptor encoding gene pfeA (PA 2688) and pirA (PA0931) failed to be stimulated by 4 of the tested synthetic catecholate siderophores whose chemical structures resemble enterobactin. Ferric-enterobactin also failed to stimulate growth of the double pfeA-pirA mutant although, like its synthetic analogues, it stimulated growth of the corresponding single mutants. Hence, we confirmed that pirA represents a second P. aeruginosa ferric-enterobactin receptor. The example of these two enterobactin receptors probably illustrates a more general phenomenon of siderophore receptor redundancy in P. aeruginosa. 相似文献
79.
Cell-free extracts of cowpea Rhizobium GN1 (peanut isolate) possessed reductase activity towards various ferric siderophores including its own. This activity was heat- and O2-sensitive and required NADH and flavins. Whereas NADPH could replace NADH with half-efficiency, succinate could not serve as reductant. Activity was insensitive to antimycin A and rotenone but was completely inhibited by HgCl2 (1 mM). Mg2+ (1 mM) enhanced reductase activity but Zn2+ and Cu2+ at the same concentration were inhibitory. The enzyme was located in the periplasmic fraction. 相似文献
80.
Nonribosomal peptide synthetases (NRPSs) are multimodular proteins capable of producing important peptide natural products. Using an assembly line process, the amino acid substrate and peptide intermediates are passed between the active sites of different catalytic domains of the NRPS while bound covalently to a peptidyl carrier protein (PCP) domain. Examination of the linker sequences that join the NRPS adenylation and PCP domains identified several conserved proline residues that are not found in standalone adenylation domains. We examined the roles of these proline residues and neighboring conserved sequences through mutagenesis and biochemical analysis of the reaction catalyzed by the adenylation domain and the fully reconstituted NRPS pathway. In particular, we identified a conserved LPxP motif at the start of the adenylation‐PCP linker. The LPxP motif interacts with a region on the adenylation domain to stabilize a critical catalytic lysine residue belonging to the A10 motif that immediately precedes the linker. Further, this interaction with the C‐terminal subdomain of the adenylation domain may coordinate movement of the PCP with the conformational change of the adenylation domain. Through this work, we extend the conserved A10 motif of the adenylation domain and identify residues that enable proper adenylation domain function. Proteins 2014; 82:2691–2702. © 2014 Wiley Periodicals, Inc. 相似文献