Touch and go: tying TonB to transport

Postle, Kathleen; Kadner, Robert J.

doi:10.1046/j.1365-2958.2003.03629.x

Cited by 291 publications

(246 citation statements)

References 87 publications

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“…The hxu system in H. influenzae type b encodes a heme utilization system that captures heme sequestered in a complex with hemopexin (14)(15)(16). The TonB-ExbBD system has a vital role in transducing the energy of the proton motor force to generate conformational changes in TonB-dependent outer membrane transporters (68). If the upregulation of outer membrane-associated iron uptake system proteins is functionally relevant to the conditions induced by treatment of strain 86-028NP with H 2 O 2 , then the concomitant upregulation of expression of the proteins needed to energize their function would be a logical step.…”

Section: Resultsmentioning

confidence: 99%

The OxyR Regulon in Nontypeable Haemophilus influenzae

et al. 2007

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Nontypeable Haemophilus influenzae (NTHi) is a gram-negative bacterium and a common commensal organism of the upper respiratory tract in humans. NTHi causes a number of diseases, including otitis media, sinusitis, conjunctivitis, exacerbations of chronic obstructive pulmonary disease, and bronchitis. During the course of colonization and infection, NTHi must withstand oxidative stress generated by insult due to multiple reactive oxygen species produced endogenously by other copathogens and by host cells. Using an NTHi-specific microarray containing oligonucleotides representing the 1821 open reading frames of the recently sequenced NTHi isolate 86-028NP, we have identified 40 genes in strain 86-028NP that are upregulated after induction of oxidative stress due to hydrogen peroxide. Further comparisons between the parent and an isogenic oxyR mutant identified a subset of 11 genes that were transcriptionally regulated by OxyR, a global regulator of oxidative stress. Interestingly, hydrogen peroxide induced the OxyR-independent upregulation of expression of the genes encoding components of multiple iron utilization systems. This finding suggested that careful balancing of levels of intracellular iron was important for minimizing the effects of oxidative stress during NTHi colonization and infection and that there are additional regulatory pathways involved in iron utilization.In the evolution of life, a delicate physiological balance has arisen to compensate for both an organism's need for oxygen and the attendant lethal consequences of oxygen's toxicity. For example, in the electron transport chain, electrons can be inadvertently transferred from redox-active proteins to oxygen, producing reactive oxygen species (ROS) such as superoxide and hydrogen peroxide (H 2 O 2 ). The effects of ROS on cells can then be exacerbated by the presence of free iron which, via the Fenton reaction, can react with H 2 O 2 to produce more highly reactive hydroxyl radicals (34, 40, 52). Within a host, this problem is compounded by the release of extracellular ROS by phagocytes, which again, can have deleterious effects on invading pathogens (13). Thus, bacteria have evolved an array of increasingly well-defined mechanisms to abrogate the effects of oxidative stress. Proteins involved in such processes include catalase, which decomposes H 2 O 2 , and members of both the AhpCF/TsaA family of alkylhydroperoxidases and the organic hydroperoxide resistance proteins (Ohr) that decompose organic peroxides. Also, DNA-binding ferritin-like proteins (Dps) sequester free iron and bind to DNA, thus protecting DNA from damage (27,33,45,53,59,60,67). In addition, many bacterial species possess genes encoding OxyR, a global regulator of antioxidant defenses (24, 66).Protection against oxidative stress is especially important to nontypeable Haemophilus influenzae (NTHi). NTHi is one of three bacterial commensal organisms, the others being Streptococcus pneumoniae and Moraxella catarrhalis, which can ascend a virus-compromised eustachian tube and caus...

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Section: Resultsmentioning

confidence: 99%

The OxyR Regulon in Nontypeable Haemophilus influenzae

et al. 2007

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“…the Ole e1 allergen (extensin-family of proteins) and short N-terminal TonB signature. The bacterial TonB-dependent receptor proteins are involved in the energized transport of siderophoremetal complexes through the membranes (Postle and Kadner 2003). Interestingly, when expressed in yeast, the TcOle e 1 enhanced the toxic eVects of Cu and, even more pronounced, of Cd.…”

Section: Discussionmentioning

confidence: 99%

Isolation of Zn-responsive genes from two accessions of the hyperaccumulator plant Thlaspi caerulescens

Hassinen

Tervahauta

Halimaa

et al. 2006

Planta

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Several populations with diVerent metal tolerance, uptake and root-to-shoot transport are known for the metal hyperaccumulator plant Thlaspi caerulescens. In this study, genes diVerentially expressed under various Zn exposures were identiWed from the shoots of two T. caerulescens accessions (calaminous and non-calaminous) using Xuorescent diVerential display RT-PCR. cDNA fragments from 16 Zn-responsive genes, including those encoding metallothionein (MT) type 2 and type 3, MRP-like transporter, pectin methylesterase (PME) and Ole e 1-like gene as well as several unknown genes, were eventually isolated. The fulllength MT2 and MT3 sequences diVer from those previously isolated from other Thlaspi accessions, possibly representing new alleles or isoforms. Besides the diVerential expression in Zn exposures, the gene expression was dependent on the accession. Thlaspi homologues of ClpP protease and MRP transporter were induced at high Zn concentrations. MT2 and PME were expressed at higher levels in the calaminous accession. The MTs and MRP transporter expressed in transgenic yeasts were capable of conferring Cu and Cd tolerance, whereas the Ole e 1-like gene enhanced toxicity to these metals. The MTs increased yeast intracellular Cd content. As no signiWcant diVerences were found between Arabidopsis and Thlaspi MTs, they apparently do not diVer in their capacity to bind metals. However, the higher levels of MT2 in the calaminous accession may contribute to the Zn-adapted phenotype.

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“…More specifically, three of the five partial HL IV genomes (W2, W4 and W12) contain genes for Ton-dependent siderophore acquisition (tonB, tolQ, cirA and fepBCD) (Figure 3a). In this pathway, proteins TolQ, R and TonB channel energy generated by protonmotive force to CirA, an Fe-ligand binding protein in the outer membrane, to power transport of the Feligand into the periplasm (Ratledge and Dover, 2000;Postle and Kadner, 2003). The Fe-ligand complex is then transported across the cytoplasmic membrane by FebB, Cand D, where Fe can be stripped from the ligand and utilized.…”

Section: Adaptations To Low Iron Environmentsmentioning

confidence: 99%

Ecology of uncultured Prochlorococcus clades revealed through single-cell genomics and biogeographic analysis

et al. 2012

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Prochlorococcus is the numerically dominant photosynthetic organism throughout much of the world’s oceans, yet little is known about the ecology and genetic diversity of populations inhabiting tropical waters. To help close this gap, we examined natural Prochlorococcus communities in the tropical Pacific Ocean using a single-cell whole-genome amplification and sequencing. Analysis of the gene content of just 10 single cells from these waters added 394 new genes to the Prochlorococcus pan-genome—that is, genes never before seen in a Prochlorococcus cell. Analysis of marker genes, including the ribosomal internal transcribed sequence, from dozens of individual cells revealed several representatives from two uncultivated clades of Prochlorococcus previously identified as HNLC1 and HNLC2. While the HNLC clades can dominate Prochlorococcus communities under certain conditions, their overall geographic distribution was highly restricted compared with other clades of Prochlorococcus. In the Atlantic and Pacific oceans, these clades were only found in warm waters with low Fe and high inorganic P levels. Genomic analysis suggests that at least one of these clades thrives in low Fe environments by scavenging organic-bound Fe, a process previously unknown in Prochlorococcus. Furthermore, the capacity to utilize organic-bound Fe appears to have been acquired horizontally and may be exchanged among other clades of Prochlorococcus. Finally, one of the single Prochlorococcus cells sequenced contained a partial genome of what appears to be a prophage integrated into the genome.

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Touch and go: tying TonB to transport

Cited by 291 publications

References 87 publications

The OxyR Regulon in Nontypeable Haemophilus influenzae

The OxyR Regulon in Nontypeable Haemophilus influenzae

Isolation of Zn-responsive genes from two accessions of the hyperaccumulator plant Thlaspi caerulescens

Ecology of uncultured Prochlorococcus clades revealed through single-cell genomics and biogeographic analysis

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