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Magalon A. History of Maturation of Prokaryotic Molybdoenzymes-A Personal View. Molecules 2023; 28:7195. [PMID: 37894674 PMCID: PMC10609526 DOI: 10.3390/molecules28207195] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2023] [Revised: 10/11/2023] [Accepted: 10/17/2023] [Indexed: 10/29/2023] Open
Abstract
In prokaryotes, the role of Mo/W enzymes in physiology and bioenergetics is widely recognized. It is worth noting that the most diverse family of Mo/W enzymes is exclusive to prokaryotes, with the probable existence of several of them from the earliest forms of life on Earth. The structural organization of these enzymes, which often include additional redox centers, is as diverse as ever, as is their cellular localization. The most notable observation is the involvement of dedicated chaperones assisting with the assembly and acquisition of the metal centers, including Mo/W-bisPGD, one of the largest organic cofactors in nature. This review seeks to provide a new understanding and a unified model of Mo/W enzyme maturation.
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Affiliation(s)
- Axel Magalon
- Aix Marseille Université, CNRS, Laboratoire de Chimie Bactérienne (UMR7283), IMM, IM2B, 13402 Marseille, France
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2
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Functional mononuclear molybdenum enzymes: challenges and triumphs in molecular cloning, expression, and isolation. J Biol Inorg Chem 2020; 25:547-569. [PMID: 32279136 DOI: 10.1007/s00775-020-01787-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2020] [Accepted: 03/30/2020] [Indexed: 10/24/2022]
Abstract
Mononuclear molybdenum enzymes catalyze a variety of reactions that are essential in the cycling of nitrogen, carbon, arsenic, and sulfur. For decades, the structure and function of these crucial enzymes have been investigated to develop a fundamental knowledge for this vast family of enzymes and the chemistries they carry out. Therefore, obtaining abundant quantities of active enzyme is necessary for exploring this family's biochemical capability. This mini-review summarizes the methods for overexpressing mononuclear molybdenum enzymes in the context of the challenges encountered in the process. Effective methods for molybdenum cofactor synthesis and incorporation, optimization of expression conditions, improving isolation of active vs. inactive enzyme, incorporation of additional prosthetic groups, and inclusion of redox enzyme maturation protein chaperones are discussed in relation to the current molybdenum enzyme literature. This article summarizes the heterologous and homologous expression studies providing underlying patterns and potential future directions.
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3
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Connelly KRS, Stevenson C, Kneuper H, Sargent F. Biosynthesis of selenate reductase in Salmonella enterica: critical roles for the signal peptide and DmsD. MICROBIOLOGY-SGM 2016; 162:2136-2146. [PMID: 27902441 PMCID: PMC5203670 DOI: 10.1099/mic.0.000381] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Salmonella enterica serovar Typhimurium is a Gram-negative bacterium with a flexible respiratory capability. Under anaerobic conditions, S. enterica can utilize a range of terminal electron acceptors, including selenate, to sustain respiratory electron transport. The S. enterica selenate reductase is a membrane-bound enzyme encoded by the ynfEFGH-dmsD operon. The active enzyme is predicted to comprise at least three subunits where YnfE is a molybdenum-containing catalytic subunit. The YnfE protein is synthesized with an N-terminal twin-arginine signal peptide and biosynthesis of the enzyme is coordinated by a signal peptide binding chaperone called DmsD. In this work, the interaction between S. enterica DmsD and the YnfE signal peptide has been studied by chemical crosslinking. These experiments were complemented by genetic approaches, which identified the DmsD binding epitope within the YnfE signal peptide. YnfE signal peptide residues L24 and A28 were shown to be important for assembly of an active selenate reductase. Conversely, a random genetic screen identified the DmsD V16 residue as being important for signal peptide recognition and selenate reductase assembly.
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Affiliation(s)
| | - Calum Stevenson
- School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Holger Kneuper
- School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Frank Sargent
- School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
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4
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Leimkühler S, Iobbi-Nivol C. Bacterial molybdoenzymes: old enzymes for new purposes. FEMS Microbiol Rev 2015; 40:1-18. [PMID: 26468212 DOI: 10.1093/femsre/fuv043] [Citation(s) in RCA: 79] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/05/2015] [Indexed: 02/06/2023] Open
Abstract
Molybdoenzymes are widespread in eukaryotic and prokaryotic organisms where they play crucial functions in detoxification reactions in the metabolism of humans and bacteria, in nitrate assimilation in plants and in anaerobic respiration in bacteria. To be fully active, these enzymes require complex molybdenum-containing cofactors, which are inserted into the apoenzymes after folding. For almost all the bacterial molybdoenzymes, molybdenum cofactor insertion requires the involvement of specific chaperones. In this review, an overview on the molybdenum cofactor biosynthetic pathway is given together with the role of specific chaperones dedicated for molybdenum cofactor insertion and maturation. Many bacteria are involved in geochemical cycles on earth and therefore have an environmental impact. The roles of molybdoenzymes in bioremediation and for environmental applications are presented.
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Affiliation(s)
- Silke Leimkühler
- Institute of Biochemistry and Biology, Department of Molecular Enzymology, University of Potsdam, 14476 Potsdam, Germany
| | - Chantal Iobbi-Nivol
- The Laboratoire de Bioénergétique et Ingénierie des Protéines, Institut de Microbiologie de la Méditerranée, CNRS, Aix Marseille Université, 13402 Marseille cedex 20, France
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5
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Cherak SJ, Turner RJ. Influence of GTP on system specific chaperone - Twin arginine signal peptide interaction. Biochem Biophys Res Commun 2015; 465:753-7. [PMID: 26299930 DOI: 10.1016/j.bbrc.2015.08.079] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2015] [Accepted: 08/18/2015] [Indexed: 11/30/2022]
Abstract
Many bacterial respiratory redox enzymes depend on the twin-arginine translocase (Tat) system for translocation and membrane insertion. Tat substrates contain an N-terminal twin-arginine (SRRxFLK) motif serving as the targeting signal towards the translocon. Many Tat substrates have a system specific chaperone - redox enzyme maturation protein (REMP) - for final folding and assembly prior to Tat binding. The REMP DmsD strongly interacts with the twin-arginine motif of the DmsA signal sequence of dimethyl sulfoxide (DMSO) reductase. In this study, we have utilized the in vitro protein-protein interaction technique of an affinity pull down assay, as well as protein thermal stability measurement via differential scanning fluorimetry (DSF) to investigate the interaction of guanosine nucleotides (GNPs) with DmsD. Here we have shown highly cooperative binding of DmsD with GTP. A dissociative ligand-binding style isotherm was generated upon GTP titration into the DmsD:DmsAL interaction, yielding sigmoidal release of DmsD with a Hill coefficient of 2.09 and a dissociation constant of 0.99 mM. DSF further illustrated the change in thermal stability upon DmsD interaction with DmsAL and GTP. These results imply the possibility of DmsD detection and binding of GTP during the DMSO protein maturation mechanism, from ribosomal translation to membrane targeting and final assembly. Conceivably, GTP is shown to act as a molecular regulator in the biochemical pathway.
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Affiliation(s)
- Stephana J Cherak
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, T2N 1N4, Canada
| | - Raymond J Turner
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, T2N 1N4, Canada.
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6
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Bay DC, Chan CS, Turner RJ. NarJ subfamily system specific chaperone diversity and evolution is directed by respiratory enzyme associations. BMC Evol Biol 2015; 15:110. [PMID: 26067063 PMCID: PMC4464133 DOI: 10.1186/s12862-015-0412-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2015] [Accepted: 06/04/2015] [Indexed: 12/04/2022] Open
Abstract
Background Redox enzyme maturation proteins (REMPs) describe a diverse family of prokaryotic chaperones involved in the biogenesis of anaerobic complex iron sulfur molybdoenzyme (CISM) respiratory systems. Many REMP family studies have focused on NarJ subfamily members from Escherichia coli: NarJ, NarW, DmsD, TorD and YcdY. The aim of this bioinformatics study was to expand upon the evolution, distribution and genetic association of these 5 REMP members within 130 genome sequenced taxonomically diverse species representing 324 Prokaryotic sequences. NarJ subfamily member diversity was examined at the phylum-species level and at the amino acid/nucleotide level to determine how close their genetic associations were between their respective CISM systems within phyla. Results This study revealed that NarJ members possessed unique motifs that distinguished Gram-negative from Gram-positive/Archaeal species and identified a strict genetic association with its nitrate reductase complex (narGHI) operon compared to all other members. NarW appears to be found specifically in Gammaproteobacteria. DmsD also showed close associations with the dimethylsulfoxide reductase (dmsABC) operon compared to TorD. Phylogenetic analysis revealed that YcdY has recently evolved from DmsD and that YcdY has likely diverged into 2 subfamilies linked to Zn- dependent alkaline phosphatase (ycdX) operons and a newly identified operon containing part of Zn-metallopeptidase FtsH complex component (hflC) and NADH-quinone dehydrogenase (mdaB). TorD demonstrated the greatest diversity in operon association. TorD was identifed within operons from either trimethylamine-N-oxide reductase (torAC) or formate dehydrogenase (fdhGHI), where each type of TorD had a unique motif. Additionally a subgroup of dmsD and torD members were also linked to operons with biotin sulfoxide (bisC) and polysulfide reductase (nrfD) indicating a potential role in the maturation of diverse CISM. Conclusion Examination of diverse prokaryotic NarJ subfamily members demonstrates that the evolution and genetic association of each member is uniquely biased by its CISM operon association. Electronic supplementary material The online version of this article (doi:10.1186/s12862-015-0412-3) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Denice C Bay
- Department of Biological Sciences, University of Calgary, Rm 156 Biological Science Bldg., 2500 University Dr. NW, Calgary, T2N 1 N4, AB, Canada.
| | - Catherine S Chan
- Department of Biological Sciences, University of Calgary, Rm 156 Biological Science Bldg., 2500 University Dr. NW, Calgary, T2N 1 N4, AB, Canada.
| | - Raymond J Turner
- Department of Biological Sciences, University of Calgary, Rm 156 Biological Science Bldg., 2500 University Dr. NW, Calgary, T2N 1 N4, AB, Canada.
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7
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Winstone TML, Turner RJ. Thermodynamic Characterization of the DmsD Binding Site for the DmsA Twin-Arginine Motif. Biochemistry 2015; 54:2040-51. [DOI: 10.1021/bi500891d] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Tara M. L. Winstone
- Department of Biological
Sciences, University of Calgary, 2500 University Drive Northwest, Calgary, AB, Canada T2N 1N4
| | - Raymond J. Turner
- Department of Biological
Sciences, University of Calgary, 2500 University Drive Northwest, Calgary, AB, Canada T2N 1N4
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8
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Chan CS, Song X, Qazi SJS, Setiaputra D, Yip CK, Chao TC, Turner RJ. Unusual pairing between assistants: interaction of the twin-arginine system-specific chaperone DmsD with the chaperonin GroEL. Biochem Biophys Res Commun 2015; 456:841-6. [PMID: 25522883 DOI: 10.1016/j.bbrc.2014.12.046] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2014] [Accepted: 12/09/2014] [Indexed: 11/25/2022]
Abstract
DmsD is a system-specific chaperone that mediates the biogenesis and maturation of DMSO reductase in Escherichia coli. It is required for DmsAB holoenzyme formation and its targeting to the cytoplasmic membrane for translocation by the twin-arginine translocase. Previous studies suggested that DmsD also interacts with general molecular chaperones to assist in folding of the reductase subunits. Here, the interaction between DmsD and GroEL was further characterized to understand the role of GroEL in DMSO reductase maturation. The inherently weak interaction between the two was strengthened in vivo under growth conditions that induce DMSO reductase expression, and the DmsD-GroEL complex showed negligible change in hydrodynamic diameter by dynamic light scattering when cross-linked. Mapping the cross-linked sites on DmsD shows that the GroEL binding site is in close proximity to the previously characterized DmsA leader binding site. These findings support a role of GroEL in DMSO reductase maturation that likely involves its chaperonin function for assisting in folding of the DmsA preprotein.
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Affiliation(s)
- Catherine S Chan
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada; Department of Biochemistry and Molecular Biology, The University of British Columbia, Vancouver, British Columbia, Canada
| | - Xiao Song
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada
| | - S Junaid S Qazi
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada
| | - Dheva Setiaputra
- Department of Biochemistry and Molecular Biology, The University of British Columbia, Vancouver, British Columbia, Canada
| | - Calvin K Yip
- Department of Biochemistry and Molecular Biology, The University of British Columbia, Vancouver, British Columbia, Canada
| | - Tzu-Chiao Chao
- Institute of Environmental Change and Society, University of Regina, Regina, Saskatchewan, Canada
| | - Raymond J Turner
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
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9
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Abstract
The transition element molybdenum (Mo) is of primordial importance for biological systems, because it is required by enzymes catalyzing key reactions in the global carbon, sulfur, and nitrogen metabolism. To gain biological activity, Mo has to be complexed by a special cofactor. With the exception of bacterial nitrogenase, all Mo-dependent enzymes contain a unique pyranopterin-based cofactor coordinating a Mo atom at their catalytic site. Various types of reactions are catalyzed by Mo-enzymes in prokaryotes including oxygen atom transfer, sulfur or proton transfer, hydroxylation, or even nonredox reactions. Mo-enzymes are widespread in prokaryotes and many of them were likely present in the Last Universal Common Ancestor. To date, more than 50--mostly bacterial--Mo-enzymes are described in nature. In a few eubacteria and in many archaea, Mo is replaced by tungsten bound to the same unique pyranopterin. How Mo-cofactor is synthesized in bacteria is reviewed as well as the way until its insertion into apo-Mo-enzymes.
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10
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‘Come into the fold’: A comparative analysis of bacterial redox enzyme maturation protein members of the NarJ subfamily. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1838:2971-2984. [DOI: 10.1016/j.bbamem.2014.08.020] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2014] [Revised: 07/24/2014] [Accepted: 08/15/2014] [Indexed: 11/19/2022]
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11
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Yokoyama K, Leimkühler S. The role of FeS clusters for molybdenum cofactor biosynthesis and molybdoenzymes in bacteria. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1853:1335-49. [PMID: 25268953 DOI: 10.1016/j.bbamcr.2014.09.021] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2014] [Revised: 09/19/2014] [Accepted: 09/22/2014] [Indexed: 11/29/2022]
Abstract
The biosynthesis of the molybdenum cofactor (Moco) has been intensively studied, in addition to its insertion into molybdoenzymes. In particular, a link between the assembly of molybdoenzymes and the biosynthesis of FeS clusters has been identified in the recent years: 1) the synthesis of the first intermediate in Moco biosynthesis requires an FeS-cluster containing protein, 2) the sulfurtransferase for the dithiolene group in Moco is also involved in the synthesis of FeS clusters, thiamin and thiolated tRNAs, 3) the addition of a sulfido-ligand to the molybdenum atom in the active site additionally involves a sulfurtransferase, and 4) most molybdoenzymes in bacteria require FeS clusters as redox active cofactors. In this review we will focus on the biosynthesis of the molybdenum cofactor in bacteria, its modification and insertion into molybdoenzymes, with an emphasis to its link to FeS cluster biosynthesis and sulfur transfer.
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Affiliation(s)
- Kenichi Yokoyama
- Department of Biochemistry, Duke University Medical Center, Durham, NC, USA
| | - Silke Leimkühler
- Department of Molecular Enzymology, Institute of Biochemistry and Biology, University of Potsdam, 14476 Potsdam, Germany.
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12
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Rivardo F, Leach TGH, Chan CS, Winstone TML, Ladner CL, Sarfo KJ, Turner RJ. Unique Photobleaching Phenomena of the Twin-Arginine Translocase Respiratory Enzyme Chaperone DmsD. Open Biochem J 2014; 8:1-11. [PMID: 24497893 PMCID: PMC3912628 DOI: 10.2174/1874091x01408010001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2013] [Revised: 11/27/2013] [Accepted: 12/01/2013] [Indexed: 11/22/2022] Open
Abstract
DmsD is a chaperone of the redox enzyme maturation protein family specifically required for biogenesis of DMSO reductase in Escherichia coli. It exists in multiple folding forms, all of which are capable of binding its known substrate, the twin-arginine leader sequence of the DmsA catalytic subunit. It is important for maturation of the reductase and targeting to the cytoplasmic membrane for translocation. Here, we demonstrate that DmsD exhibits an irreversible photobleaching phenomenon upon 280 nm excitation irradiation. The phenomenon is due to quenching of the tryptophan residues in DmsD and is dependent on its folding and conformation. We also show that a tryptophan residue involved in DmsA signal peptide binding (W87) is important for photobleaching of DmsD. Mutation of W87, or binding of the DmsA twin-arginine signal peptide to DmsD in the pocket that includes W72, W80, and W91 significantly affects the degree of photobleaching. This study highlights the advantage of a photobleaching phenomenon to study protein folding and conformation changes within a protein that was once considered unusable in fluorescence spectroscopy.
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Affiliation(s)
- Fabrizio Rivardo
- BI 156, Department of Biological Sciences, University of Calgary, 2500 University Dr NW, Calgary, Alberta, Canada T2N 1N4
| | - Thorin G H Leach
- BI 156, Department of Biological Sciences, University of Calgary, 2500 University Dr NW, Calgary, Alberta, Canada T2N 1N4
| | - Catherine S Chan
- BI 156, Department of Biological Sciences, University of Calgary, 2500 University Dr NW, Calgary, Alberta, Canada T2N 1N4
| | - Tara M L Winstone
- BI 156, Department of Biological Sciences, University of Calgary, 2500 University Dr NW, Calgary, Alberta, Canada T2N 1N4
| | - Carol L Ladner
- BI 156, Department of Biological Sciences, University of Calgary, 2500 University Dr NW, Calgary, Alberta, Canada T2N 1N4
| | - Kwabena J Sarfo
- BI 156, Department of Biological Sciences, University of Calgary, 2500 University Dr NW, Calgary, Alberta, Canada T2N 1N4
| | - Raymond J Turner
- BI 156, Department of Biological Sciences, University of Calgary, 2500 University Dr NW, Calgary, Alberta, Canada T2N 1N4
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Winstone TML, Tran VA, Turner RJ. The hydrophobic region of the DmsA twin-arginine leader peptide determines specificity with chaperone DmsD. Biochemistry 2013; 52:7532-41. [PMID: 24093457 PMCID: PMC3812903 DOI: 10.1021/bi4009374] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
![]()
The
system specific chaperone DmsD plays a role in the maturation
of the catalytic subunit of dimethyl sulfoxide (DMSO) reductase, DmsA.
Pre-DmsA contains a 45-amino acid twin-arginine leader peptide that
is important for targeting and translocation of folded and cofactor-loaded
DmsA by the twin-arginine translocase. DmsD has previously been shown
to interact with the complete twin-arginine leader peptide of DmsA.
In this study, isothermal titration calorimetry was used to investigate
the thermodynamics of binding between synthetic peptides composed
of different portions of the DmsA leader peptide and DmsD. Only those
peptides that included the complete and contiguous hydrophobic region
of the DmsA leader sequence were able to bind DmsD with a 1:1 stoichiometry.
Each of the peptides that were able to bind DmsD also showed some
α-helical structure as indicated by circular dichroism spectroscopy.
Differential scanning calorimetry revealed that DmsD gained very little
thermal stability upon binding any of the DmsA leader peptides tested.
Together, these results suggest that a portion of the hydrophobic
region of the DmsA leader peptide determines the specificity of binding
and may produce helical properties
upon binding to DmsD. Overall, this study demonstrates that the recognition
of the DmsA twin-arginine leader sequence by the DmsD chaperone shows
unexpected rules and confirms further that the biochemistry of the
interaction of the chaperone with their leaders demonstrates differences
in their molecular interactions.
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Affiliation(s)
- Tara M L Winstone
- Department of Biological Sciences, University of Calgary , 2500 University Drive Northwest, Calgary, AB, Canada T2N 1N4
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14
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Stevens CM, Okon M, McIntosh LP, Paetzel M. ¹H, ¹³C and ¹⁵N resonance assignments and peptide binding site chemical shift perturbation mapping for the Escherichia coli redox enzyme chaperone DmsD. BIOMOLECULAR NMR ASSIGNMENTS 2013; 7:193-197. [PMID: 22766963 DOI: 10.1007/s12104-012-9408-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2012] [Accepted: 06/21/2012] [Indexed: 06/01/2023]
Abstract
Herein are reported the mainchain (1)H, (13)C and (15)N chemical shift assignments and amide (15)N relaxation data for Escherichia coli DmsD, a 23.3 kDa protein responsible for the correct folding and translocation of the dimethyl sulfoxide reductase enzyme complex. In addition, the observed amide chemical shift perturbations resulting from complex formation with the reductase subunit DmsA leader peptide support a model in which the 44 residue peptide makes extensive contacts across the surface of the DmsD protein.
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Affiliation(s)
- Charles M Stevens
- Department of Molecular Biology and Biochemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
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15
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James MJ, Coulthurst SJ, Palmer T, Sargent F. Signal peptide etiquette during assembly of a complex respiratory enzyme. Mol Microbiol 2013; 90:400-14. [PMID: 23961722 DOI: 10.1111/mmi.12373] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/18/2013] [Indexed: 12/25/2022]
Abstract
Salmonella enterica serovar Typhimurium is a Gram-negative pathogen capable of respiration with a number of terminal electron acceptors. Tetrathionate reductase is important for the infection process and is encoded by the ttrBCA operon where TtrA and TtrB are metallocofactor-containing proteins targeted to the periplasmic side of the membrane by two different Tat targeting peptides. In this work, the inter-relationship between these two signal peptides has been explored. Molecular genetics and biochemical approaches reveal that the processing of the TtrB Tat signal peptide is dependent on the successful assembly of its partner protein, TtrA. Inactivation of either the TtrA or the TtrB Tat targeting peptides individually was observed to have limited overall effects on assembly of the enzyme or on cellular tetrathionate reductase activity. However, inactivation of both signal peptides simultaneously was found to completely abolish physiological tetrathionate reductase activity. These data suggest both signals are normally active during assembly of the enzyme, and imply a code of conduct exists between the signal peptides where one can compensate for inactivity in the other. Since it appears likely that tetrathionate reductase presents itself for export as a multi-signal complex, these observations also have implications for the mechanism of the bacterial Tat translocase.
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Affiliation(s)
- Martyn J James
- College of Life Sciences, University of Dundee, Dundee, DD1 5EH, Scotland, UK
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16
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Abstract
The Tat (twin-arginine translocation) system is a protein targeting pathway utilized by prokaryotes and chloroplasts. Tat substrates are produced with distinctive N-terminal signal peptides and are translocated as fully folded proteins. In Escherichia coli, Tat-dependent proteins often contain redox cofactors that must be loaded before translocation. Trimethylamine N-oxide reductase (TorA) is a model bacterial Tat substrate and is a molybdenum cofactor-dependent enzyme. Co-ordination of cofactor loading and translocation of TorA is directed by the TorD protein, which is a cytoplasmic chaperone known to interact physically with the TorA signal peptide. In the present study, a pre-export TorAD complex has been characterized using biochemical and biophysical techniques, including SAXS (small-angle X-ray scattering). A stable, cofactor-free TorAD complex was isolated, which revealed a 1:1 binding stoichiometry. Surprisingly, a TorAD complex with similar architecture can be isolated in the complete absence of the 39-residue TorA signal peptide. The present study demonstrates that two high-affinity binding sites for TorD are present on TorA, and that a single TorD protein binds both of those simultaneously. Further characterization suggested that the C-terminal ‘Domain IV’ of TorA remained solvent-exposed in the cofactor-free pre-export TorAD complex. It is possible that correct folding of Domain IV upon cofactor loading is the trigger for TorD release and subsequent export of TorA.
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17
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Iobbi-Nivol C, Leimkühler S. Molybdenum enzymes, their maturation and molybdenum cofactor biosynthesis in Escherichia coli. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2012. [PMID: 23201473 DOI: 10.1016/j.bbabio.2012.11.007] [Citation(s) in RCA: 117] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Molybdenum cofactor (Moco) biosynthesis is an ancient, ubiquitous, and highly conserved pathway leading to the biochemical activation of molybdenum. Moco is the essential component of a group of redox enzymes, which are diverse in terms of their phylogenetic distribution and their architectures, both at the overall level and in their catalytic geometry. A wide variety of transformations are catalyzed by these enzymes at carbon, sulfur and nitrogen atoms, which include the transfer of an oxo group or two electrons to or from the substrate. More than 50 molybdoenzymes were identified in bacteria to date. In molybdoenzymes Mo is coordinated to a dithiolene group on the 6-alkyl side chain of a pterin called molybdopterin (MPT). The biosynthesis of Moco can be divided into four general steps in bacteria: 1) formation of the cyclic pyranopterin monophosphate, 2) formation of MPT, 3) insertion of molybdenum into molybdopterin to form Moco, and 4) additional modification of Moco with the attachment of GMP or CMP to the phosphate group of MPT, forming the dinucleotide variant of Moco. This review will focus on molybdoenzymes, the biosynthesis of Moco, and its incorporation into specific target proteins focusing on Escherichia coli. This article is part of a Special Issue entitled: Metals in Bioenergetics and Biomimetics Systems.
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Affiliation(s)
- Chantal Iobbi-Nivol
- Institut de Microbiologie de la Méditerranée, Aix Marseille Université, Marseille, France
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18
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Purification of a Tat leader peptide by co-expression with its chaperone. Protein Expr Purif 2012; 84:167-72. [DOI: 10.1016/j.pep.2012.05.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2012] [Revised: 05/03/2012] [Accepted: 05/06/2012] [Indexed: 11/22/2022]
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Shanmugham A, Bakayan A, Völler P, Grosveld J, Lill H, Bollen YJM. The hydrophobic core of twin-arginine signal sequences orchestrates specific binding to Tat-pathway related chaperones. PLoS One 2012; 7:e34159. [PMID: 22479549 PMCID: PMC3316669 DOI: 10.1371/journal.pone.0034159] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2011] [Accepted: 02/27/2012] [Indexed: 11/19/2022] Open
Abstract
Redox enzyme maturation proteins (REMPs) bind pre-proteins destined for translocation across the bacterial cytoplasmic membrane via the twin-arginine translocation system and enable the enzymatic incorporation of complex cofactors. Most REMPs recognize one specific pre-protein. The recognition site usually resides in the N-terminal signal sequence. REMP binding protects signal peptides against degradation by proteases. REMPs are also believed to prevent binding of immature pre-proteins to the translocon. The main aim of this work was to better understand the interaction between REMPs and substrate signal sequences. Two REMPs were investigated: DmsD (specific for dimethylsulfoxide reductase, DmsA) and TorD (specific for trimethylamine N-oxide reductase, TorA). Green fluorescent protein (GFP) was genetically fused behind the signal sequences of TorA and DmsA. This ensures native behavior of the respective signal sequence and excludes any effects mediated by the mature domain of the pre-protein. Surface plasmon resonance analysis revealed that these chimeric pre-proteins specifically bind to the cognate REMP. Furthermore, the region of the signal sequence that is responsible for specific binding to the corresponding REMP was identified by creating region-swapped chimeric signal sequences, containing parts of both the TorA and DmsA signal sequences. Surprisingly, specificity is not encoded in the highly variable positively charged N-terminal region of the signal sequence, but in the more similar hydrophobic C-terminal parts. Interestingly, binding of DmsD to its model substrate reduced membrane binding of the pre-protein. This property could link REMP-signal peptide binding to its reported proofreading function.
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Affiliation(s)
| | | | | | | | | | - Yves J. M. Bollen
- Department of Molecular Cell Biology, VU University Amsterdam, Amsterdam, The Netherlands
- * E-mail:
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20
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Grahl S, Maillard J, Spronk CAEM, Vuister GW, Sargent F. Overlapping transport and chaperone-binding functions within a bacterial twin-arginine signal peptide. Mol Microbiol 2012; 83:1254-67. [PMID: 22329966 PMCID: PMC3712460 DOI: 10.1111/j.1365-2958.2012.08005.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The twin-arginine translocation (Tat) pathway is a protein targeting system present in many prokaryotes. The physiological role of the Tat pathway is the transmembrane translocation of fully-folded proteins, which are targeted by N-terminal signal peptides bearing conserved SRRxFLK ‘twin-arginine’ amino acid motifs. In Escherichia coli the majority of Tat targeted proteins bind redox cofactors and it is important that only mature, cofactor-loaded precursors are presented for export. Cellular processes have been unearthed that sequence these events, for example the signal peptide of the periplasmic nitrate reductase (NapA) is bound by a cytoplasmic chaperone (NapD) that is thought to regulate assembly and export of the enzyme. In this work, genetic, biophysical and structural approaches were taken to dissect the interaction between NapD and the NapA signal peptide. A NapD binding epitope was identified towards the N-terminus of the signal peptide, which overlapped significantly with the twin-arginine targeting motif. NMR spectroscopy revealed that the signal peptide adopted a α-helical conformation when bound by NapD, and substitution of single residues within the NapA signal peptide was sufficient to disrupt the interaction. This work provides an increased level of understanding of signal peptide function on the bacterial Tat pathway.
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Affiliation(s)
- Sabine Grahl
- College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
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21
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Coulthurst SJ, Dawson A, Hunter WN, Sargent F. Conserved signal peptide recognition systems across the prokaryotic domains. Biochemistry 2012; 51:1678-86. [PMID: 22289056 PMCID: PMC3290102 DOI: 10.1021/bi201852d] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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The twin-arginine translocation (Tat) pathway is a protein
targeting system found in bacteria, archaea, and chloroplasts. Proteins
are directed to the Tat translocase by N-terminal signal peptides
containing SRRxFLK “twin-arginine” amino acid motifs.
The key feature of the Tat system is its ability to transport fully
folded proteins across ionically sealed membranes. For this reason
the Tat pathway has evolved for the assembly of extracytoplasmic redox
enzymes that must bind cofactors, and so fold, prior to export. It
is important that only cofactor-loaded, folded precursors are presented
for export, and cellular processes have been unearthed that regulate
signal peptide activity. One mechanism, termed “Tat proofreading”,
involves specific signal peptide binding proteins or chaperones. The
archetypal Tat proofreading chaperones belong to the TorD family,
which are dedicatedto the assembly of molybdenum-dependent redox
enzymes in bacteria. Here, a gene cluster was identified in the archaeon Archaeoglobus fulgidusthat is predicted to encode a putative
molybdenum-dependent tetrathionate reductase. The gene cluster also
encodes a TorD family chaperone (AF0160 or TtrD) and in this work
TtrD is shown to bind specifically to the Tat signal peptide of the
TtrA subunit of the tetrathionate reductase. In addition, the 3D crystal
structure of TtrD is presented at 1.35 Å resolution and a nine-residue
binding epitope for TtrD is identified within the TtrA signal peptide
close to the twin-arginine targeting motif. This work suggests that
archaea may employ a chaperone-dependent Tat proofreading system that
is similar to that utilized by bacteria.
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Affiliation(s)
- Sarah J Coulthurst
- College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
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22
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Hou B, Brüser T. The Tat-dependent protein translocation pathway. Biomol Concepts 2011; 2:507-23. [DOI: 10.1515/bmc.2011.040] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2011] [Accepted: 08/05/2011] [Indexed: 11/15/2022] Open
Abstract
AbstractThe twin-arginine translocation (Tat) pathway is found in bacteria, archaea, and plant chloroplasts, where it is dedicated to the transmembrane transport of fully folded proteins. These proteins contain N-terminal signal peptides with a specific Tat-system binding motif that is recognized by the transport machinery. In contrast to other protein transport systems, the Tat system consists of multiple copies of only two or three usually small (∼8–30 kDa) membrane proteins that oligomerize to two large complexes that transiently interact during translocation. Only one of these complexes includes a polytopic membrane protein, TatC. The other complex consists of TatA. Tat systems of plants, proteobacteria, and several other phyla contain a third component, TatB. TatB is evolutionarily and structurally related to TatA and usually forms tight complexes with TatC. Minimal two-component Tat systems lacking TatB are found in many bacterial and archaeal phyla. They consist of a ‘bifunctional’ TatA that also covers TatB functionalities, and a TatC. Recent insights into the structure and interactions of the Tat proteins have various important implications.
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Affiliation(s)
- Bo Hou
- Institute of Microbiology, Leibniz University Hannover, Schneiderberg 50, D-30167 Hannover, Germany
| | - Thomas Brüser
- Institute of Microbiology, Leibniz University Hannover, Schneiderberg 50, D-30167 Hannover, Germany
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23
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Magalon A, Fedor JG, Walburger A, Weiner JH. Molybdenum enzymes in bacteria and their maturation. Coord Chem Rev 2011. [DOI: 10.1016/j.ccr.2010.12.031] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
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24
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Parasuram R, Lee JS, Yin P, Somarowthu S, Ondrechen MJ. Functional classification of protein 3D structures from predicted local interaction sites. J Bioinform Comput Biol 2011; 8 Suppl 1:1-15. [PMID: 21155016 DOI: 10.1142/s0219720010005166] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2010] [Revised: 08/25/2010] [Accepted: 09/10/2010] [Indexed: 11/18/2022]
Abstract
A new approach to the functional classification of protein 3D structures is described with application to some examples from structural genomics. This approach is based on functional site prediction with THEMATICS and POOL. THEMATICS employs calculated electrostatic potentials of the query structure. POOL is a machine learning method that utilizes THEMATICS features and has been shown to predict accurate, precise, highly localized interaction sites. Extension to the functional classification of structural genomics proteins is now described. Predicted functionally important residues are structurally aligned with those of proteins with previously characterized biochemical functions. A 3D structure match at the predicted local functional site then serves as a more reliable predictor of biochemical function than an overall structure match. Annotation is confirmed for a structural genomics protein with the ribulose phosphate binding barrel (RPBB) fold. A putative glucoamylase from Bacteroides fragilis (PDB ID 3eu8) is shown to be in fact probably not a glucoamylase. Finally a structural genomics protein from Streptomyces coelicolor annotated as an enoyl-CoA hydratase (PDB ID 3g64) is shown to be misannotated. Its predicted active site does not match the well-characterized enoyl-CoA hydratases of similar structure but rather bears closer resemblance to those of a dehalogenase with similar fold.
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Affiliation(s)
- Ramya Parasuram
- Department of Chemistry & Chemical Biology, Northeastern University, Boston, MA 02115, USA
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25
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Kostecki JS, Li H, Turner RJ, DeLisa MP. Visualizing interactions along the Escherichia coli twin-arginine translocation pathway using protein fragment complementation. PLoS One 2010; 5:e9225. [PMID: 20169075 PMCID: PMC2821923 DOI: 10.1371/journal.pone.0009225] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2009] [Accepted: 01/18/2010] [Indexed: 11/23/2022] Open
Abstract
The twin-arginine translocation (Tat) pathway is well known for its ability to export fully folded substrate proteins out of the cytoplasm of Gram-negative and Gram-positive bacteria. Studies of this mechanism in Escherichia coli have identified numerous transient protein-protein interactions that guide export-competent proteins through the Tat pathway. To visualize these interactions, we have adapted bimolecular fluorescence complementation (BiFC) to detect protein-protein interactions along the Tat pathway of living cells. Fragments of the yellow fluorescent protein (YFP) were fused to soluble and transmembrane factors that participate in the translocation process including Tat substrates, Tat-specific proofreading chaperones and the integral membrane proteins TatABC that form the translocase. Fluorescence analysis of these YFP chimeras revealed a wide range of interactions such as the one between the Tat substrate dimethyl sulfoxide reductase (DmsA) and its dedicated proofreading chaperone DmsD. In addition, BiFC analysis illuminated homo- and hetero-oligomeric complexes of the TatA, TatB and TatC integral membrane proteins that were consistent with the current model of translocase assembly. In the case of TatBC assemblies, we provide the first evidence that these complexes are co-localized at the cell poles. Finally, we used this BiFC approach to capture interactions between the putative Tat receptor complex formed by TatBC and the DmsA substrate or its dedicated chaperone DmsD. Our results demonstrate that BiFC is a powerful approach for studying cytoplasmic and inner membrane interactions underlying bacterial secretory pathways.
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Affiliation(s)
- Jan S. Kostecki
- Department of Biomedical Engineering, Cornell University, Ithaca, New York, United States of America
| | - Haiming Li
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada
| | - Raymond J. Turner
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada
| | - Matthew P. DeLisa
- Department of Biomedical Engineering, Cornell University, Ithaca, New York, United States of America
- School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York, United States of America
- * E-mail:
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26
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Li H, Chang L, Howell JM, Turner RJ. DmsD, a Tat system specific chaperone, interacts with other general chaperones and proteins involved in the molybdenum cofactor biosynthesis. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2010; 1804:1301-9. [PMID: 20153451 DOI: 10.1016/j.bbapap.2010.01.022] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2009] [Revised: 12/23/2009] [Accepted: 01/28/2010] [Indexed: 10/19/2022]
Abstract
Many bacterial oxidoreductases depend on the Tat translocase for correct cell localization. Substrates for the Tat translocase possess twin-arginine leaders. System specific chaperones or redox enzyme maturation proteins (REMPs) are a group of proteins implicated in oxidoreductase maturation. DmsD is a REMP discovered in Escherichia coli, which interacts with the twin-arginine leader sequence of DmsA, the catalytic subunit of DMSO reductase. In this study, we identified several potential interacting partners of DmsD by using several in vitro protein-protein interaction screening approaches, including affinity chromatography, co-precipitation, and cross-linking. Candidate hits from these in vitro findings were analyzed by in vivo methods of bacterial two-hybrid (BACTH) and bimolecular fluorescence complementation (BiFC). From these data, DmsD was confirmed to interact with the general molecular chaperones DnaK, DnaJ, GrpE, GroEL, Tig and Ef-Tu. In addition, DmsD was also found to interact with proteins involved in the molybdenum cofactor biosynthesis pathway. Our data suggests that DmsD may play a role as a "node" in escorting its substrate through a cascade of chaperone assisted protein-folding maturation events.
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Affiliation(s)
- Haiming Li
- Department of Biological Sciences, Faculty of Science, University of Calgary, Calgary, Alberta, Canada T2N 1N4
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27
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Genest O, Méjean V, Iobbi-Nivol C. Multiple roles of TorD-like chaperones in the biogenesis of molybdoenzymes. FEMS Microbiol Lett 2009; 297:1-9. [DOI: 10.1111/j.1574-6968.2009.01660.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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28
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Ramasamy SK, Clemons WM. Structure of the twin-arginine signal-binding protein DmsD from Escherichia coli. Acta Crystallogr Sect F Struct Biol Cryst Commun 2009; 65:746-50. [PMID: 19652330 DOI: 10.1107/s1744309109023811] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2009] [Accepted: 06/21/2009] [Indexed: 11/10/2022]
Abstract
The translocation of folded proteins via the twin-arginine translocation (Tat) pathway is regulated to prevent the futile export of inactive substrate. DmsD is part of a class of cytoplasmic chaperones that play a role in preventing certain redox proteins from premature transport. DmsD from Escherichia coli has been crystallized in space group P4(1)2(1)2, with unit-cell parameters a = b = 97.45, c = 210.04 A, in the presence of a small peptide. The structure has been solved by molecular replacement to a resolution of 2.4 A and refined to an R factor of 19.4%. There are four molecules in the asymmetric unit that may mimic a higher order structure in vivo. There appears to be density for the peptide in a predicted binding pocket, which lends support to its role as the signal-recognition surface for this class of proteins.
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Affiliation(s)
- Suresh Kumar Ramasamy
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
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29
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Guymer D, Maillard J, Sargent F. A genetic analysis of in vivo selenate reduction by Salmonella enterica serovar Typhimurium LT2 and Escherichia coli K12. Arch Microbiol 2009; 191:519-28. [DOI: 10.1007/s00203-009-0478-7] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2009] [Revised: 04/01/2009] [Accepted: 04/06/2009] [Indexed: 11/28/2022]
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30
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Stevens CM, Winstone TML, Turner RJ, Paetzel M. Structural analysis of a monomeric form of the twin-arginine leader peptide binding chaperone Escherichia coli DmsD. J Mol Biol 2009; 389:124-33. [PMID: 19361518 DOI: 10.1016/j.jmb.2009.03.069] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2009] [Revised: 03/27/2009] [Accepted: 03/31/2009] [Indexed: 11/20/2022]
Abstract
The redox enzyme maturation proteins play an essential role in the proofreading and membrane targeting of protein substrates to the twin-arginine translocase. Functionally, the most thoroughly characterized redox enzyme maturation protein to date is Escherichia coli DmsD (EcDmsD). Herein, we present the X-ray crystal structure of the monomeric form of the EcDmsD refined to 2.0 A resolution, with clear electron density present for each of its 204 amino acid residues. The structural data presented here complement the biochemical data previously generated regarding the function of these twin-arginine translocase leader peptide binding chaperone proteins. Docking and molecular dynamics simulation experiments were used to provide a proposed model for how this chaperone is able to recognize the leader peptide of its substrate DmsA. The interactions observed in the model are in agreement with previous biochemical data and suggest intimate interactions between the conserved twin-arginine motif of the leader peptide of E. coli DmsA and the most conserved regions on the surface of EcDmsD.
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Affiliation(s)
- Charles M Stevens
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada
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31
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Buchanan G, Maillard J, Nabuurs SB, Richardson DJ, Palmer T, Sargent F. Features of a twin-arginine signal peptide required for recognition by a Tat proofreading chaperone. FEBS Lett 2008; 582:3979-84. [DOI: 10.1016/j.febslet.2008.10.049] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2008] [Revised: 10/17/2008] [Accepted: 10/20/2008] [Indexed: 10/21/2022]
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