Ulrike Kappler

University of Queensland , Brisbane, Queensland, Australia

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Publications (63)210.45 Total impact

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    ABSTRACT: The Ralstonia solanacearum species complex has long been recognized as a group of phenotypically diverse strains that can be subdivided into four phylotypes. Using a polyphasic taxonomic approach on an extensive set of strains, this study provides evidence for a taxonomic and nomenclatural revision of members of this complex. Data obtained from phylogenetic analysis of 16S rRNA gene sequences, 16S-23S rRNA intergenic spacer (ITS) region sequences, partial endoglucanase (egl) gene sequences and DNA-DNA hybridizations demonstrate that the Ralstonia solanacearum species complex is comprised of three genospecies. One of these includes the type strain of R. solanacearum and consists of R. solanacearum phylotype II strains only. The second genospecies includes the type strain of R. syzygii and contains only phylotype IV strains. This genospecies is subdivided into three distinct groups, namely R. syzygii, the causal agent of Sumatra disease on clove trees in Indonesia, R. solanacearum phylotype IV strains isolated from different host plants mostly from Indonesia, and strains of the blood disease bacterium (BDB), the causal agent of the Banana Blood Disease, a bacterial wilt disease in Indonesia affecting bananas and plantains. The last genospecies is composed of R. solanacearum strains belonging to phylotypes I and III. As these genospecies are also supported by phenotypic data that allow the differentiation of the three genospecies, the following taxonomic proposals are made: emendation of the descriptions of R. solanacearum and R. syzygii, descriptions of Ralstonia syzygii subsp. syzygii (R 001T = LMG 10661T = DSM 7385T) for the current R. syzygii strains, Ralstonia syzygii subsp. indonesiensis subsp. nov. (UQRS 464T = LMG 27703T = DSM 27478T) for the current R. solanacearum phylotype IV strains, Ralstonia syzygii subsp. celebesensis subsp. nov. (UQRS 627T = LMG 27706T = DSM 27477T) for the BDB strains and Ralstonia pseudosolanacearum sp. nov. (UQRS 461T = LMG 9673T = NCPPB 1029T) for the R. solanacearum phylotype I and III strains.
    International journal of systematic and evolutionary microbiology. 06/2014;
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    ABSTRACT: Sulfite dehydrogenase from the soil bacterium Sinorhizobium meliloti (SorT) is a periplasmic, homodimeric molybdoenzyme with a molecular mass of 78 kDa. It differs from most other well studied sulfite oxidizing enzymes as it bears no heme cofactor. SorT does not readily reduce ferrous horse heart cytochrome c which is the preferred electron acceptor for vertebrate sulfite oxidases. In the present study, ferrocene methanol (FM) (in its oxidized ferrocenium form) was utilised as an artificial electron acceptor for the catalytic SorT sulfite oxidation reaction. Cyclic voltammetry of FM was used to generate the active form of the mediator at the electrode surface. The FM-mediated catalytic sulfite oxidation by SorT was investigated by two different voltammetric methods namely (i) SorT freely diffusing in solution and (ii) SorT confined to a thin layer at the electrode surface by a semi-permeable dialysis membrane. A single set of rate and equilibrium constants was used to simulate the catalytic voltammograms performed under different sweep rates and with various concentrations of sulfite and FM which provides new insights into the kinetics of SorT catalytic mechanism. Further, we were able to model the role of the dialysis membrane in the kinetics of the overall catalytic system.
    The journal of physical chemistry. B. 06/2014;
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    ABSTRACT: Haemophilus influenzae is a host adapted human pathogen known to contribute to a variety of acute and chronic diseases of the upper and lower respiratory tract as well as the middle ear. At the sites of infection as well as during growth as a commensal the environmental conditions encountered by H. influenzae will vary significantly, especially in terms of oxygen availability, however, the mechanisms by which the bacteria can adapt their metabolism to cope with such changes have not been studied in detail. Using targeted metabolomics the spectrum of metabolites produced during growth of H. influenzae on glucose in RPMI-based medium was found to change from acetate as the main product during aerobic growth to formate as the major product during anaerobic growth. This change in end-product is likely caused by a switch in the major route of pyruvate degradation. Neither lactate nor succinate or fumarate were major products of H. influenzae growth under any condition studied. Gene expression studies and enzyme activity data revealed that despite an identical genetic makeup and very similar metabolite production profiles, H. influenzae strain Rd appeared to favor glucose degradation via the pentose phosphate pathway, while strain 2019, a clinical isolate, showed higher expression of enzymes involved in glycolysis. Components of the respiratory chain were most highly expressed during microaerophilic and anaerobic growth in both strains, but again clear differences existed in the expression of genes associated e.g., with NADH oxidation, nitrate and nitrite reduction in the two strains studied. Together our results indicate that H. influenzae uses a specialized type of metabolism that could be termed "respiration assisted fermentation" where the respiratory chain likely serves to alleviate redox imbalances caused by incomplete glucose oxidation, and at the same time provides a means of converting a variety of compounds including nitrite and nitrate that arise as part of the host defence mechanisms.
    Frontiers in Microbiology 01/2014; 5:69. · 3.90 Impact Factor
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    ABSTRACT: We describe the catalytic voltammetry of the periplasmic arsenite oxidase (Aio) from the chemolithoautotrophic bacterium Rhizobium sp. str. NT-26 that oxidizes arsenite to arsenate. Electrochemistry of the enzyme was accomplished using its native electron transfer partner, cytochrome c552 (cyt c552), as a mediator. The protein cyt c552 adsorbed on a mercaptoundecanoic acid (MUA) modified Au electrode exhibited a stable, reversible one-electron voltammetric response at +275mV vs NHE (pH7). In the presence of arsenite and Aio the voltammetry of cyt c552 is transformed from a transient response to an amplified sigmoidal (steady state) wave consistent with an electro-catalytic system. Digital simulation was performed using single set of enzyme dependent parameters for all catalytic voltammetry obtained at different sweep rates and various substrate concentrations. The obtained kinetic constants from digital simulation provide new insight into the kinetics of the NT-26 Aio catalytic mechanism.
    Biochimica et Biophysica Acta 07/2013; · 4.66 Impact Factor
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    ABSTRACT: NtrYX is a sensor-histidine kinase/response regulator two-component system that has had limited characterization in a small number of α-Proteobacteria. Phylogenetic analysis of the response regulator, NtrX, showed that this two-component system is extensively distributed across the bacterial domain and it is present in a variety of β-Proteobacteria, including the human pathogen Neisseria gonorrhoeae. Microarray analysis revealed that the expression of several components of the respiratory chain was reduced in a N. gonorrhoeae ntrX mutant compared to the isogenic wild-type strain 1291. These included the cytochrome c oxidase subunit (ccoP), nitrite reductase (aniA) and nitric oxide reductase (norB). Enzyme activity assays showed decreased cytochrome oxidase and nitrite reductase activities in the ntrX mutant, consistent with microarray data. N. gonorrhoeae ntrX mutants had reduced capacity to survive inside primary cervical cells compared to the wild-type, and although they retained the ability to form a biofilm, they exhibited reduced survival within the biofilm compared to wild-type cells, as indicated by live-dead staining. Analyses of an ntrX mutant in a representative α-Proteobacterium, Rhodobacter capsulatus, showed that cytochrome oxidase activity was also reduced compared to the wild-type strain, SB1003. Taken together, these data provide evidence that the NtrYX two component-system may be a key regulator in the expression of respiratory enzymes and, in particular, cytochrome c oxidase, across a wide range of proteobacteria, including a variety of bacterial pathogens.
    Journal of bacteriology 04/2013; · 3.94 Impact Factor
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    ABSTRACT: NtrYX is a sensor-histidine kinase/response regulator two-component system that has had limited characterization in a small number of Alphaproteobacteria. Phylogenetic analysis of the response regulator NtrX showed that this two-component system is extensively distributed across the bacterial domain, and it is present in a variety of Betaproteobacteria, including the human pathogen Neisseria gonorrhoeae. Microarray analysis revealed that the expression of several components of the respiratory chain was reduced in an N. gonorrhoeae ntrX mutant compared to that in the isogenic wild-type (WT) strain 1291. These included the cytochrome c oxidase subunit (ccoP), nitrite reductase (aniA), and nitric oxide reductase (norB). Enzyme activity assays showed decreased cytochrome oxidase and nitrite reductase activities in the ntrX mutant, consistent with microarray data. N. gonorrhoeae ntrX mutants had reduced capacity to survive inside primary cervical cells compared to the wild type, and although they retained the ability to form a biofilm, they exhibited reduced survival within the biofilm compared to wild-type cells, as indicated by LIVE/DEAD staining. Analyses of an ntrX mutant in a representative alphaproteobacterium, Rhodobacter capsulatus, showed that cytochrome oxidase activity was also reduced compared to that in the wild-type strain SB1003. Taken together, these data provide evidence that the NtrYX two-component system may be a key regulator in the expression of respiratory enzymes and, in particular, cytochrome c oxidase, across a wide range of proteobacteria, including a variety of bacterial pathogens.
  • Ulrike Kappler, Amanda S Nouwens
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    ABSTRACT: Molybdenum enzymes are known to underpin key reactions in the biological carbon, nitrogen and sulfur cycles, however, the diversity of these enzymes and the reactions they catalyze especially in bacteria is much greater than currently known. We have analysed the molybdoproteome of the soil bacterium Starkeya novella as a function of growth mode and identified a complete pathway for Mo-PPT synthesis, a Mo transporter and 18 gene loci encoding mononuclear Mo-enzymes of the Xanthine Oxidase, Sulfite Oxidase and DMSO Reductase enzyme families. This relatively high number of Mo enzymes may be a specific property of the taxonomic group (Xanthobacteraceae) to which S. novella belongs. About 70% of S. novella Mo enzymes have no characterized close relatives, and two thirds of them are expressed under the conditions analysed, which included heterotrophy, methylotrophy, chemolithotrophy and mixotrophy. Many enzymes were clearly regulated in response to either the type of carbon source present in the growth medium or the presence of thiosulfate, and two, in particular, including an uncharacterized enzyme of the XO family (Snov_3370) were highly abundant under all growth conditions tested. We also uncovered novel enzymes with links to growth in the presence of thiosulfate, such as a PaoABC-type aldehyde oxidoreductase and an uncharacterized group 1 sulfite oxidase family enzyme, although the function of these enzymes during sulfur oxidation is unclear at present. Clearly, further work is needed to uncover the significance of these enzymes for cell metabolism.
    Metallomics 01/2013; · 4.10 Impact Factor
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    ABSTRACT: The arsenite oxidase (Aio) from the facultative autotrophic Alphaproteobacterium Rhizobium sp. NT-26 is a bioenergetic enzyme involved in the oxidation of arsenite to arsenate. The enzyme from the distantly related heterotroph, Alcaligenes faecalis, which is thought to oxidise arsenite for detoxification, consists of a large α subunit (AioA) with bis-molybdopterin guanine dinucleotide at its active site and a 3Fe-4S cluster, and a small β subunit (AioB) which contains a Rieske 2Fe-2S cluster. The successful heterologous expression of the NT-26 Aio in Escherichia coli has resulted in the solution of its crystal structure. The NT-26 Aio, a heterotetramer, shares high overall similarity to the heterodimeric arsenite oxidase from A. faecalis but there are striking differences in the structure surrounding the Rieske 2Fe-2S cluster which we demonstrate explains the difference in the observed redox potentials (+225 mV vs. +130/160 mV, respectively). A combination of site-directed mutagenesis and electron paramagnetic resonance was used to explore the differences observed in the structure and redox properties of the Rieske cluster. In the NT-26 AioB the substitution of a serine (S126 in NT-26) for a threonine as in the A. faecalis AioB explains a -20 mV decrease in redox potential. The disulphide bridge in the A. faecalis AioB which is conserved in other betaproteobacterial AioB subunits and the Rieske subunit of the cytochrome bc 1 complex is absent in the NT-26 AioB subunit. The introduction of a disulphide bridge had no effect on Aio activity or protein stability but resulted in a decrease in the redox potential of the cluster. These results are in conflict with previous data on the betaproteobacterial AioB subunit and the Rieske of the bc 1 complex where removal of the disulphide bridge had no effect on the redox potential of the former but a decrease in cluster stability was observed in the latter.
    PLoS ONE 01/2013; 8(8):e72535. · 3.73 Impact Factor
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    Ulrike Kappler, Amanda S Nouwens
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    ABSTRACT: The highly diverse and metabolically versatile microbial communities found in soil environments are major contributors to the global carbon, nitrogen, and sulfur cycles. We have used a combination of genome -based pathway analysis with proteomics and gene expression studies to investigate metabolic adaptation in a representative of these bacteria, Starkeya novella, which was originally isolated from agricultural soil. This bacterium was the first facultative sulfur chemolithoautotroph that was isolated and it is also able to grow with methanol and on over 39 substrates as a heterotroph. However, using glucose, fructose, methanol, thiosulfate as well as combinations of the carbon compounds with thiosulfate as growth substrates we have demonstrated here that contrary to the previous classification, S. novella is not a facultative sulfur chemolitho- and methylotroph, as the enzyme systems required for these two growth modes are always expressed at high levels. This is typical for key metabolic pathways. In addition enzymes for various pathways of carbon dioxide fixation were always expressed at high levels, even during heterotrophic growth on glucose or fructose, which suggests a role for these pathways beyond the generation of reduced carbon units for cell growth, possibly in redox balancing of metabolism. Our results then indicate that S. novella, a representative of the Xanthobacteraceae family of methylotrophic soil and freshwater dwelling bacteria, employs a mixotrophic growth strategy under all conditions tested here. As a result the contribution of this bacterium to either carbon sequestration or the release of climate active substances could vary very quickly, which has direct implications for the modeling of such processes if mixotrophy proves to be the main growth strategy for large populations of soil bacteria.
    Frontiers in Microbiology 01/2013; 4:304. · 3.90 Impact Factor
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    ABSTRACT: (Starkey 1934) Kelly . 2000 is a member of the family in the order , which is thus far poorly characterized at the genome level. Cultures from this species are most interesting due to their facultatively chemolithoautotrophic lifestyle, which allows them to both consume carbon dioxide and to produce it. This feature makes an interesting model organism for studying the genomic basis of regulatory networks required for the switch between consumption and production of carbon dioxide, a key component of the global carbon cycle. In addition, is of interest for its ability to grow on various inorganic sulfur compounds and several C1-compounds such as methanol. Besides , is only the second species in the family with a completely sequenced genome of a type strain. The current taxonomic classification of this group is in significant conflict with the 16S rRNA data. The genomic data indicate that the physiological capabilities of the organism might have been underestimated. The 4,765,023 bp long chromosome with its 4,511 protein-coding and 52 RNA genes was sequenced as part of the DOE Joint Genome Institute Community Sequencing Program (CSP) 2008.
    Standards in Genomic Sciences 10/2012; 7(1):44-58. · 2.01 Impact Factor
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    ABSTRACT: We have investigated the potential of the GTP synthesis pathways as chemotherapeutic targets in the human pathogen Cryptococcus neoformans, a common cause of fatal fungal meningoencephalitis. We find that de novo GTP biosynthesis, but not the alternate salvage pathway, is critical to cryptococcal dissemination and survival in vivo. Loss of inosine monophosphate dehydrogenase (IMPDH) in the de novo pathway results in slow growth and virulence factor defects, while loss of the cognate phosphoribosyltransferase in the salvage pathway yielded no phenotypes. Further, the Cryptococcus species complex displays variable sensitivity to the IMPDH inhibitor mycophenolic acid, and we uncover a rare drug-resistant subtype of C. gattii that suggests an adaptive response to microbial IMPDH inhibitors in its environmental niche. We report the structural and functional characterization of IMPDH from Cryptococcus, revealing insights into the basis for drug resistance and suggesting strategies for the development of fungal-specific inhibitors. The crystal structure reveals the position of the IMPDH moveable flap and catalytic arginine in the open conformation for the first time, plus unique, exploitable differences in the highly conserved active site. Treatment with mycophenolic acid led to significantly increased survival times in a nematode model, validating de novo GTP biosynthesis as an antifungal target in Cryptococcus.
    PLoS Pathogens 10/2012; 8(10):e1002957. · 8.14 Impact Factor
  • Ulrike Kappler, Megan J Maher
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    ABSTRACT: SoxAX cytochromes are heme-thiolate proteins that play a key role in bacterial thiosulfate oxidation, where they initiate the reaction cycle of a multi-enzyme complex by catalyzing the attachment of sulfur substrates such as thiosulfate to a conserved cysteine present in a carrier protein. SoxAX proteins have a wide phylogenetic distribution and form a family with at least three distinct types of SoxAX protein. The types of SoxAX cytochromes differ in terms of the number of heme groups present in the proteins (there are diheme and triheme versions) as well as in their subunit structure. While two of the SoxAX protein types are heterodimers, the third group contains an additional subunit, SoxK, that stabilizes the complex of the SoxA and SoxX proteins. Crystal structures are available for representatives of the two heterodimeric SoxAX protein types and both of these have shown that the cysteine ligand to the SoxA active site heme carries a modification to a cysteine persulfide that implicates this ligand in catalysis. EPR studies of SoxAX proteins have also revealed a high complexity of heme dependent signals associated with this active site heme; however, the exact mechanism of catalysis is still unclear at present, as is the exact number and types of redox centres involved in the reaction.
    Cellular and Molecular Life Sciences CMLS 08/2012; · 5.62 Impact Factor
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    ABSTRACT: The X-ray crystal structure of oxidised pseudoazurin from the denitrifying plant symbiotic bacterium Sinorhizobium meliloti (SmPAz2) has been solved to a resolution of 2.0Å. The pseudoazurin from Sinorhizobium sp. is unusual as it forms an operon with a sulfite dehydrogenase enzyme, rather than a Cu nitrite reductase. Examination of the structure reveals that the geometric parameters of the Type I Cu site in SmPAz2 correlate with observed features in the electronic spectrum of the protein. Comparison of the structure of SmPAz2 with those of pseudoazurins from five other bacterial species shows that the surface of SmPAz2 bears a conserved hydrophobic patch encircled by positively-charged residues, which may serve as a recognition site for its redox partners.
    Journal of inorganic biochemistry 05/2012; 115:148-54. · 3.25 Impact Factor
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    ABSTRACT: SoxAX cytochromes catalyze the formation of heterodisulfide bonds between inorganic sulfur compounds and a carrier protein, SoxYZ. They contain unusual His/Cys-ligated heme groups with complex spectroscopic signatures. The heme-ligating cysteine has been implicated in SoxAX catalysis, but neither the SoxAX spectroscopic properties nor its catalysis are fully understood at present. We have solved the first crystal structure for a group 2 SoxAX protein (SnSoxAX), where an N-terminal extension of SoxX forms a novel structure that supports dimer formation. Crystal structures of SoxAX with a heme ligand substitution (C236M) uncovered an inherent flexibility of this SoxA heme site, with both bonding distances and relative ligand orientation differing between asymmetric units and the new residue, Met236, representing an unusual rotamer of methionine. The flexibility of the SnSoxAXC236M SoxA heme environment is probably the cause of the four distinct, new EPR signals, including a high spin ferric heme form, that were observed for the enzyme. Despite the removal of the catalytically active cysteine heme ligand and drastic changes in the redox potential of the SoxA heme (WT, −479 mV; C236M, +85 mV), the substituted enzyme was catalytically active in glutathione-based assays although with reduced turnover numbers (WT, 3.7 s−1; C236M, 2.0 s−1). SnSoxAXC236M was also active in assays using SoxYZ and thiosulfate as the sulfur substrate, suggesting that Cys236 aids catalysis but is not crucial for it. The SoxYZ-based SoxAX assay is the first assay for an isolated component of the Sox multienzyme system.
    Journal of Biological Chemistry 07/2011; 286(28):24872-24881. · 4.65 Impact Factor
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    ABSTRACT: SoxAX cytochromes catalyze the formation of heterodisulfide bonds between inorganic sulfur compounds and a carrier protein, SoxYZ. They contain unusual His/Cys-ligated heme groups with complex spectroscopic signatures. The heme-ligating cysteine has been implicated in SoxAX catalysis, but neither the SoxAX spectroscopic properties nor its catalysis are fully understood at present. We have solved the first crystal structure for a group 2 SoxAX protein (SnSoxAX), where an N-terminal extension of SoxX forms a novel structure that supports dimer formation. Crystal structures of SoxAX with a heme ligand substitution (C236M) uncovered an inherent flexibility of this SoxA heme site, with both bonding distances and relative ligand orientation differing between asymmetric units and the new residue, Met(236), representing an unusual rotamer of methionine. The flexibility of the SnSoxAX(C236M) SoxA heme environment is probably the cause of the four distinct, new EPR signals, including a high spin ferric heme form, that were observed for the enzyme. Despite the removal of the catalytically active cysteine heme ligand and drastic changes in the redox potential of the SoxA heme (WT, -479 mV; C236M, +85 mV), the substituted enzyme was catalytically active in glutathione-based assays although with reduced turnover numbers (WT, 3.7 s(-1); C236M, 2.0 s(-1)). SnSoxAX(C236M) was also active in assays using SoxYZ and thiosulfate as the sulfur substrate, suggesting that Cys(236) aids catalysis but is not crucial for it. The SoxYZ-based SoxAX assay is the first assay for an isolated component of the Sox multienzyme system.
    Journal of Biological Chemistry 05/2011; 286(28):24872-81. · 4.65 Impact Factor
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    Ulrike Kappler
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    ABSTRACT: Enzymes belonging to the Sulfite Oxidase (SO) enzyme family are found in virtually all forms of life, and are especially abundant in prokaryotes as shown by analysis of available genome data. Despite this fact, only a limited number of bacterial SO family enzymes has been characterized in detail to date, and these appear to be involved in very different metabolic processes such as energy generation from sulfur compounds, host colonization, sulfite detoxification and organosulfonate degradation. The few characterized bacterial SO family enzymes also show an intriguing range of structural conformations, including monomeric, dimeric and heterodimeric enzymes with varying numbers and types of redox centres. Some of the bacterial enzymes even catalyze novel reactions such as dimethylsulfoxide reduction that previously had been thought not to be catalyzed by SO family enzymes. Classification of the SO family enzymes based on the structure of their Mo domain clearly shows that three distinct groups of enzymes belong to this family, and that almost all SOEs characterized to date are representatives of the same group. The widespread occurrence and obvious structural and functional plasticity of the bacterial SO family enzymes make this an exciting field for further study, in particular the unraveling of the metabolic roles of the three enzyme groups, some of which appear to be associated almost exclusively with pathogenic microorganisms.
    Biochimica et Biophysica Acta 01/2011; 1807(1):1-10. · 4.66 Impact Factor
  • Abstracts of Papers of the American Chemical Society, v.231 (2006). 01/2011;
  • D. Mikkelsen, U. Kappler, A. McEwan, L. Sly
    01/2011;
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    ABSTRACT: Sulfite dehydrogenase (SDH) from Starkeya novella is a heterodimeric enzyme comprising a Mo active site and a heme c electron relay, which mediates electron transfer from the Mo cofactor to cytochrome c following sulfite oxidation. Studies on the wild type enzyme (SDH(WT)) and its variants have identified key amino acids at the active site, specifically Arg-55 and His-57. We report the Mo(VI/V), Mo(V/IV) and Fe(III/II) (heme) redox potentials of the variants SDH(R55K), SDH(R55M), SDH(R55Q) and SDH(H57A) in comparison with those of SDH(WT). For SDH(R55M), SDH(R55Q) and SDH(H57A) the heme potentials are lowered from ca. 240mV in SDH(WT) to ca. 200mV, while the heme potential in SDH(R55K) remains unchanged and the Mo redox potentials are not affected significantly in any of these variants. Protein film voltammetry reveals a pH dependence of the electrochemical catalytic half-wave potential (E(cat)) of -59mV/pH in SDH(WT) and SDH(R55K) which tracks the pH dependence of the Mo(VI/V) redox potential. By contrast, the catalytic potentials for SDH(R55M) and SDH(H57A) are pH-independent and follow the potential of the heme cofactor. These results highlight a switch in the pathway of electron exchange as a function of applied potential that is revealed by protein film voltammetry where an actuation of rate limiting intramolecular electron transfer (IET, Mo to heme) at high potential attenuates the catalytic current relative to faster, direct electron transfer (Mo to electrode) at lower potential. The same change in electron transfer pathway is linked to an unusual peak-shaped profile of the ideally sigmoidal steady state voltammogram in SDH(WT) alone, which has been associated with a potential dependent change in the orientation of the enzyme on the electrode surface. All other variants show purely sigmoidal voltammetry due to their inherently slower turnover numbers which are always lower than IET rates.
    Biochimica et Biophysica Acta 01/2011; 1807(1):108-18. · 4.66 Impact Factor
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    ABSTRACT: This paper describes a highly sensitive electrochemical (voltammetric) determination of sulfite using a combination of Starkeya novella sulfite dehydrogenase (SDH), horse heart cytochrome c (cyt c), and a self-assembled monolayer of 11-mercaptoundecanol (MU) cast on a gold electrode. The biosensor was optimized in terms of pH and the ratio of cyt c/SDH. The electrocatalytic oxidation current of sulfite increased linearly from 1 to 6 microM at the enzyme-modified electrode with a correlation coefficient of 0.9995 and an apparent Michaelis constant (K(M,app)) of 43 microM. Using an amperometric method, the low detection limit for sulfite at the enzyme-modified electrode was 44 pM (signal-to-noise ratio = 3). The modified electrode retained a stable response for 3 days while losing only ca. 4% of its initial sensitivity during a 2 week storage period in 50 mM Tris buffer solution at 4 degrees C. The enzyme electrode was successfully used for the determination of sulfite in beer and white wine samples. The results of these electrochemical analyses agreed well with an independent spectrophotometric method using Ellman's reagent, but the detection limit was far superior using the electrochemical method.
    Analytical Chemistry 09/2010; 82(17):7374-9. · 5.70 Impact Factor

Publication Stats

731 Citations
210.45 Total Impact Points

Institutions

  • 2001–2013
    • University of Queensland 
      • School of Chemistry and Molecular Biosciences
      Brisbane, Queensland, Australia
    • University of Bonn
      • Institut für Mikrobiologie und Biotechnologie
      Bonn, North Rhine-Westphalia, Germany
  • 2004–2009
    • The University of Arizona
      • Department of Chemistry and Biochemistry (College of Science)
      Tucson, AZ, United States
  • 2007
    • University College London
      Londinium, England, United Kingdom
  • 2000
    • Universität Regensburg
      • Lehrstuhl für Biochemie I
      Regensburg, Bavaria, Germany