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Bacteria in an intense competition for iron: Key component of the Campylobacter jejuni iron uptake system scavenges enterobactin hydrolysis product.

ABSTRACT: To acquire essential Fe(III), bacteria produce and secrete siderophores with high affinity and selectivity for Fe(III) to mediate its uptake into the cell. Here, we show that the periplasmic binding protein CeuE of Campylobacter jejuni, which was previously thought to bind the Fe(III) complex of the hexadentate siderophore enterobactin (Kd ? 0.4 ± 0.1 µM), preferentially binds the Fe(III) complex of the tetradentate enterobactin hydrolysis product bis(2,3-dihydroxybenzoyl-l-Ser) (H5-bisDHBS) (Kd = 10.1 ± 3.8 nM). The protein selects ?-configured [Fe(bisDHBS)](2-) from a pool of diastereomeric Fe(III)-bisDHBS species that includes complexes with metal-to-ligand ratios of 1:1 and 2:3. Cocrystal structures show that, in addition to electrostatic interactions and hydrogen bonding, [Fe(bisDHBS)](2-) binds through coordination of His227 and Tyr288 to the iron center. Similar binding is observed for the Fe(III) complex of the bidentate hydrolysis product 2,3-dihydroxybenzoyl-l-Ser, [Fe(monoDHBS)2](3-) The mutation of His227 and Tyr288 to noncoordinating residues (H227L/Y288F) resulted in a substantial loss of affinity for [Fe(bisDHBS)](2-) (Kd ? 0.5 ± 0.2 µM). These results suggest a previously unidentified role for CeuE within the Fe(III) uptake system of C. jejuni, provide a molecular-level understanding of the underlying binding pocket adaptations, and rationalize reports on the use of enterobactin hydrolysis products by C. jejuni, Vibrio cholerae, and other bacteria with homologous periplasmic binding proteins.

SUBMITTER: Raines DJ

PROVIDER: S-EPMC4889360 | biostudies-literature | 2016 May

REPOSITORIES: biostudies-literature

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Bacteria in an intense competition for iron: Key component of the Campylobacter jejuni iron uptake system scavenges enterobactin hydrolysis product.

Raines Daniel J DJ Moroz Olga V OV Blagova Elena V EV Turkenburg Johan P JP Wilson Keith S KS Duhme-Klair Anne-K AK

Proceedings of the National Academy of Sciences of the United States of America 20160509 21

To acquire essential Fe(III), bacteria produce and secrete siderophores with high affinity and selectivity for Fe(III) to mediate its uptake into the cell. Here, we show that the periplasmic binding protein CeuE of Campylobacter jejuni, which was previously thought to bind the Fe(III) complex of the hexadentate siderophore enterobactin (Kd ∼ 0.4 ± 0.1 µM), preferentially binds the Fe(III) complex of the tetradentate enterobactin hydrolysis product bis(2,3-dihydroxybenzoyl-l-Ser) (H5-bisDHBS) (Kd ...[more]

PMID: 27162326

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Project description:The ferric enterobactin receptor CfrA not only is responsible for high-affinity iron acquisition in Campylobacter jejuni but also is essential for C. jejuni colonization in animal intestines. In this study, we determined the feasibility of targeting the iron-regulated outer membrane protein CfrA for immune protection against Campylobacter colonization. Alignment of complete CfrA sequences from 15 Campylobacter isolates showed that the levels of amino acid identity for CfrA range from 89% to 98%. Immunoblotting analysis using CfrA-specific antibodies demonstrated that CfrA was dramatically induced under iron-restricted conditions and was widespread and produced in 32 Campylobacter primary strains from various sources and from geographically diverse areas. The immunoblotting survey results were highly correlated with the results of an enterobactin growth promotion assay and a PCR analysis using cfrA-specific primers. Inactivation of the cfrA gene also impaired norepinephrine-mediated growth promotion, suggesting that CfrA is required for C. jejuni to sense intestinal stress hormones during colonization. Complementation of the cfrA mutant with a wild-type cfrA allele in trans fully restored the production and function of CfrA. A growth assay using purified anti-CfrA immunoglobulin G demonstrated that specific CfrA antibodies could block the function of CfrA, which diminished ferric enterobactin-mediated growth promotion under iron-restricted conditions. The inhibitory effect of CfrA antibodies was dose dependent. Immunoblotting analysis also indicated that CfrA was expressed and immunogenic in chickens experimentally infected with C. jejuni. Amino acid substitution mutagenesis demonstrated that R327, a basic amino acid that is highly conserved in CfrA, plays a critical role in ferric enterobactin acquisition in C. jejuni. Together, these findings strongly suggest that CfrA is a promising vaccine candidate for preventing and controlling Campylobacter infection in humans and animal reservoirs.

Project description:The expression of iron-regulated systems in gram-negative bacteria is generally controlled by the Fur protein, which represses the transcription of iron-regulated promoters by using Fe2+ as a cofactor. Mutational analysis of the Campylobacter jejuni fur gene was carried out by generation of a set of mutant copies of fur which had a kanamycin or chloramphenicol resistance gene introduced into the regions encoding the N and C termini of the Fur protein. The mutated genes were recombined into the C. jejuni NCTC 11168 chromosome, and putative mutants were confirmed by Southern hybridization. C. jejuni mutants were obtained only when the resistance genes were transcribed in the same orientation as the fur gene. The C. jejuni fur mutant grew slower than the parental strain. Comparison of protein profiles of fractionated C. jejuni cells grown in low- or high-iron medium indicated derepressed expression of three iron-regulated outer membrane proteins with molecular masses of 70, 75, and 80 kDa. Characterization by N-terminal amino acid sequencing showed the 75-kDa protein to be identical to CfrA, a Campylobacter coli siderophore receptor homologue, whereas the 70-kDa protein was identified as a new siderophore receptor homologue. Periplasmic fractions contained four derepressed proteins with molecular masses of 19, 29, 32, and 36 kDa. The 19-kDa protein has been previously identified, but its function is unknown. The cytoplasmic fraction contained two iron-repressed and two iron-induced proteins with molecular masses of 26, 55, 31, and 40 kDa, respectively. The two iron-repressed proteins have been previously identified as the oxidative stress defense proteins catalase (KatA) and alkyl hydroperoxide reductase (AhpC). AhpC and KatA were still iron regulated in the fur mutant, suggesting the presence of Fur-independent iron regulation. Further analysis of the C. jejuni iron and Fur regulons by using two-dimensional gel electrophoresis demonstrated the total number of iron- and Fur-regulated proteins to be lower than for other bacterial pathogens.

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Dataset Information

Bacteria in an intense competition for iron: Key component of the Campylobacter jejuni iron uptake system scavenges enterobactin hydrolysis product.

Publications

Bacteria in an intense competition for iron: Key component of the Campylobacter jejuni iron uptake system scavenges enterobactin hydrolysis product.

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