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Chaoprasid P, Lukat P, Mühlen S, Heidler T, Gazdag E, Dong S, Bi W, Rüter C, Kirchenwitz M, Steffen A, Jänsch L, Stradal TEB, Dersch P, Blankenfeldt W. Crystal structure of bacterial cytotoxic necrotizing factor CNF Y reveals molecular building blocks for intoxication. EMBO J 2021; 40:e105202. [PMID: 33410511 PMCID: PMC7883292 DOI: 10.15252/embj.2020105202] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2020] [Revised: 11/12/2020] [Accepted: 11/23/2020] [Indexed: 12/30/2022] Open
Abstract
Cytotoxic necrotizing factors (CNFs) are bacterial single-chain exotoxins that modulate cytokinetic/oncogenic and inflammatory processes through activation of host cell Rho GTPases. To achieve this, they are secreted, bind surface receptors to induce endocytosis and translocate a catalytic unit into the cytosol to intoxicate host cells. A three-dimensional structure that provides insight into the underlying mechanisms is still lacking. Here, we determined the crystal structure of full-length Yersinia pseudotuberculosis CNFY . CNFY consists of five domains (D1-D5), and by integrating structural and functional data, we demonstrate that D1-3 act as export and translocation module for the catalytic unit (D4-5) and for a fused β-lactamase reporter protein. We further found that D4, which possesses structural similarity to ADP-ribosyl transferases, but had no equivalent catalytic activity, changed its position to interact extensively with D5 in the crystal structure of the free D4-5 fragment. This liberates D5 from a semi-blocked conformation in full-length CNFY , leading to higher deamidation activity. Finally, we identify CNF translocation modules in several uncharacterized fusion proteins, which suggests their usability as a broad-specificity protein delivery tool.
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Affiliation(s)
- Paweena Chaoprasid
- Institute of InfectiologyCenter for Molecular Biology of Inflammation (ZMBE)University of MünsterMünsterGermany
- Molecular Infection BiologyHelmholtz Centre for Infection ResearchBraunschweigGermany
| | - Peer Lukat
- Structure and Function of ProteinsHelmholtz Centre for Infection ResearchBraunschweigGermany
| | - Sabrina Mühlen
- Institute of InfectiologyCenter for Molecular Biology of Inflammation (ZMBE)University of MünsterMünsterGermany
- Molecular Infection BiologyHelmholtz Centre for Infection ResearchBraunschweigGermany
- Deutsches Zentrum für InfektionsforschungBraunschweigGermany
| | - Thomas Heidler
- Molecular Structural BiologyHelmholtz Centre for Infection ResearchBraunschweigGermany
| | - Emerich‐Mihai Gazdag
- Structure and Function of ProteinsHelmholtz Centre for Infection ResearchBraunschweigGermany
| | - Shuangshuang Dong
- Structure and Function of ProteinsHelmholtz Centre for Infection ResearchBraunschweigGermany
| | - Wenjie Bi
- Cellular ProteomicsHelmholtz Centre for Infection ResearchBraunschweigGermany
| | - Christian Rüter
- Institute of InfectiologyCenter for Molecular Biology of Inflammation (ZMBE)University of MünsterMünsterGermany
| | - Marco Kirchenwitz
- Cell BiologyHelmholtz Centre for Infection ResearchBraunschweigGermany
| | - Anika Steffen
- Cell BiologyHelmholtz Centre for Infection ResearchBraunschweigGermany
| | - Lothar Jänsch
- Cellular ProteomicsHelmholtz Centre for Infection ResearchBraunschweigGermany
- Institute of ZoologyTechnische Universität BraunschweigBraunschweigGermany
| | - Theresia E B Stradal
- Cell BiologyHelmholtz Centre for Infection ResearchBraunschweigGermany
- Institute of ZoologyTechnische Universität BraunschweigBraunschweigGermany
| | - Petra Dersch
- Institute of InfectiologyCenter for Molecular Biology of Inflammation (ZMBE)University of MünsterMünsterGermany
- Molecular Infection BiologyHelmholtz Centre for Infection ResearchBraunschweigGermany
- Deutsches Zentrum für InfektionsforschungBraunschweigGermany
- Institute of MicrobiologyTechnische Universität BraunschweigBraunschweigGermany
| | - Wulf Blankenfeldt
- Structure and Function of ProteinsHelmholtz Centre for Infection ResearchBraunschweigGermany
- Institute for Biochemistry, Biotechnology and BioinformaticsTechnische Universität BraunschweigBraunschweigGermany
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2
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Tak U, Vlach J, Garza-Garcia A, William D, Danilchanka O, de Carvalho LPS, Saad JS, Niederweis M. The tuberculosis necrotizing toxin is an NAD + and NADP + glycohydrolase with distinct enzymatic properties. J Biol Chem 2019; 294:3024-3036. [PMID: 30593509 PMCID: PMC6398120 DOI: 10.1074/jbc.ra118.005832] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2018] [Revised: 12/27/2018] [Indexed: 12/13/2022] Open
Abstract
Upon host infection, Mycobacterium tuberculosis secretes the tuberculosis necrotizing toxin (TNT) into the cytosol of infected macrophages, leading to host cell death by necroptosis. TNT hydrolyzes NAD+ in the absence of any exogenous cofactor, thus classifying it as a β-NAD+ glycohydrolase. However, TNT lacks sequence similarity with other NAD+ hydrolyzing enzymes and lacks the essential motifs involved in NAD+ binding and hydrolysis by these enzymes. In this study, we used NMR to examine the enzymatic activity of TNT and found that TNT hydrolyzes NADP+ as fast as NAD+ but does not cleave the corresponding reduced dinucleotides. This activity of TNT was not inhibited by ADP-ribose or nicotinamide, indicating low affinity of TNT for these reaction products. A selection assay for nontoxic TNT variants in Escherichia coli identified four of six residues in the predicted NAD+-binding pocket and four glycine residues that form a cradle directly below the NAD+-binding site, a conserved feature in the TNT protein family. Site-directed mutagenesis of residues near the predicted NAD+-binding site revealed that Phe727, Arg757, and Arg780 are essential for NAD+ hydrolysis by TNT. These results identify the NAD+-binding site of TNT. Our findings also show that TNT is an NAD+ glycohydrolase with properties distinct from those of other bacterial glycohydrolases. Because many of these residues are conserved within the TNT family, our findings provide insights into understanding the function of the >300 TNT homologs.
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Affiliation(s)
- Uday Tak
- From the Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35205 and
| | - Jiri Vlach
- From the Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35205 and
| | | | - Doreen William
- From the Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35205 and
| | - Olga Danilchanka
- From the Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35205 and
| | | | - Jamil S Saad
- From the Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35205 and
| | - Michael Niederweis
- From the Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35205 and
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3
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Abstract
Heat-labile enterotoxins (LTs) of Escherichia coli are closely related to cholera toxin (CT), which was originally discovered in 1959 in culture filtrates of the gram-negative bacterium Vibrio cholerae. Several other gram-negative bacteria also produce enterotoxins related to CT and LTs, and together these toxins form the V. cholerae-E. coli family of LTs. Strains of E. coli causing a cholera-like disease were designated enterotoxigenic E. coli (ETEC) strains. The majority of LTI genes (elt) are located on large, self-transmissible or mobilizable plasmids, although there are instances of LTI genes being located on chromosomes or carried by a lysogenic phage. The stoichiometry of A and B subunits in holotoxin requires the production of five B monomers for every A subunit. One proposed mechanism is a more efficient ribosome binding site for the B gene than for the A gene, increasing the rate of initiation of translation of the B gene independently from A gene translation. The three-dimensional crystal structures of representative members of the LT family (CT, LTpI, and LTIIb) have all been determined by X-ray crystallography and found to be highly similar. Site-directed mutagenesis has identified many residues in the CT and LT A subunits, including His44, Val53, Ser63, Val97, Glu110, and Glu112, that are critical for the structures and enzymatic activities of these enterotoxins. For the enzymatically active A1 fragment to reach its substrate, receptor-bound holotoxin must gain access to the cytosol of target cells.
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Upadhyay A, Mooyottu S, Yin H, Nair MS, Bhattaram V, Venkitanarayanan K. Inhibiting Microbial Toxins Using Plant-Derived Compounds and Plant Extracts. MEDICINES (BASEL, SWITZERLAND) 2015; 2:186-211. [PMID: 28930207 PMCID: PMC5456214 DOI: 10.3390/medicines2030186] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2015] [Revised: 07/22/2015] [Accepted: 07/23/2015] [Indexed: 06/07/2023]
Abstract
Many pathogenic bacteria and fungi produce potentially lethal toxins that cause cytotoxicity or impaired cellular function either at the site of colonization or other locations in the body through receptor-mediated interactions. Various factors, including biotic and abiotic environments, competing microbes, and chemical cues affect toxin expression in these pathogens. Recent work suggests that several natural compounds can modulate toxin production in pathogenic microbes. However, studies explaining the mechanistic basis for their effect are scanty. This review discusses the potential of various plant-derived compounds for reducing toxin production in foodborne and other microbes. In addition, studies highlighting their anti-toxigenic mechanism(s) are discussed.
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Affiliation(s)
- Abhinav Upadhyay
- Department of Animal Science, University of Connecticut, Storrs, CT 06269, USA.
| | - Shankumar Mooyottu
- Department of Animal Science, University of Connecticut, Storrs, CT 06269, USA.
| | - Hsinbai Yin
- Department of Animal Science, University of Connecticut, Storrs, CT 06269, USA.
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5
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Identification of inhibitors against the potential ligandable sites in the active cholera toxin. Comput Biol Chem 2015; 55:37-48. [DOI: 10.1016/j.compbiolchem.2015.02.011] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2014] [Revised: 01/29/2015] [Accepted: 02/04/2015] [Indexed: 11/23/2022]
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Zhang G. Design, synthesis, and evaluation of bisubstrate analog inhibitors of cholera toxin. Bioorg Med Chem Lett 2008; 18:3724-7. [PMID: 18515100 PMCID: PMC2536626 DOI: 10.1016/j.bmcl.2008.05.049] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2008] [Accepted: 05/14/2008] [Indexed: 11/15/2022]
Abstract
Bisubstrate analog inhibitors in which a nicotinamide mimic is attached to a series of structurally diversified guanidines (arginine mimics) were synthesized and evaluated for inhibition of cholera toxin. The mechanism-based bisubstrate inhibitors were up to 1400-fold more potent than the natural substrate NAD+ and 400-fold more potent than the artificial substrate diethylamino (benzylidine-amino)guanidine (DEABAG) in an assay toward an intrinsically active mutant of wild-type cholera toxin.
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Affiliation(s)
- Guangtao Zhang
- Department of Chemistry, University of Washington, PO Box 351700, Seattle, WA 98195, USA.
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7
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Order-disorder-order transitions mediate the activation of cholera toxin. J Mol Biol 2008; 377:748-60. [PMID: 18272180 DOI: 10.1016/j.jmb.2007.12.075] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2007] [Revised: 12/28/2007] [Accepted: 12/28/2007] [Indexed: 11/20/2022]
Abstract
Cholera toxin (CT) holotoxin must be activated to intoxicate host cells. This process requires the intracellular dissociation of the enzymatic CTA1 domain from the holotoxin components CTA2 and B5, followed by subsequent interaction with the host factor ADP ribosylation factor 6 (ARF6)-GTP. We report the first NMR-based solution structural data for the CT enzymatic domain (CTA1). We show that this free enzymatic domain partially unfolds at the C-terminus and binds its protein partners at both the beginning and the end of this activation process. Deviations from random coil chemical shifts (Delta delta(coil)) indicate helix formation in the activation loop, which is essential to open the toxin's active site and occurs prior to its association with human protein ARF6. We performed NMR titrations of both free CTA1 and an active CTA1:ARF6-GTP complex with NAD(+), which revealed that the formation of the complex does not significantly enhance NAD(+) binding. Partial unfolding of CTA1 is further illustrated by using 4,4'-bis(1-anilinonaphthalene 8-sulfonate) fluorescence as an indicator of the exposed hydrophobic character of the free enzyme, which is substantially reduced when bound to ARF6-GTP. We propose that the primary role of ARF6's allostery is to induce refolding of the C-terminus of CTA1. Thus, as a folded globular toxin complex, CTA1 escapes the chaperone and proteasomal components of the endoplasmic reticulum associated degradation pathway in the cytosol and then proceeds to ADP ribosylate its target G(s)alpha, triggering the downstream events associated with the pathophysiology of cholera.
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8
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Angeles DC, Song KP. Peptide antibiotic and actin-binding protein as mixed-type inhibitors of Clostridium difficile CDT toxin activities. Biochem Biophys Res Commun 2005; 327:361-70. [PMID: 15629471 DOI: 10.1016/j.bbrc.2004.11.167] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2004] [Indexed: 11/30/2022]
Abstract
CDT from Clostridium difficile is an ADP-ribosyltransferase that causes rapid actin disaggregation and cell death. For efficient catalysis, CDT required specific divalent cations and binding by NAD which can be substituted by ATP but not ADP. Increasing isolation of CDT-producing strains prompted our search for antagonists like the anti-C. difficile agents bacitracin and vancomycin which were effective CDT inhibitors. Other CDT transferase and glycohydrolase inhibitors with consistently low IC50 values were heterocyclic peptide antibiotics containing modified amino acids such as polymyxin B and beta-lactam cephalosporins. The strongest inhibitors were actin-binding proteins which possess extensive interfaces with G-actin, adjoining the CDT-ADP-ribose+ acceptor site and nucleotide cleft. Analysis of the extent and mode of inhibition and actin interaction sites provided fresh evidences on the designation of actin interface domains with actin-binding proteins. Our results uphold ADP-ribosylation as an innate physiologic process in cellular cytoskeletal reorganization regulated by endogenous metabolites.
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Affiliation(s)
- Dario Cruz Angeles
- Microbial Pathogenesis Laboratory, Department of Microbiology, Faculty of Medicine, National University of Singapore, Singapore 117597, Singapore
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9
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Zhou GC, Parikh SL, Tyler PC, Evans GB, Furneaux RH, Zubkova OV, Benjes PA, Schramm VL. Inhibitors of ADP-ribosylating bacterial toxins based on oxacarbenium ion character at their transition states. J Am Chem Soc 2004; 126:5690-8. [PMID: 15125661 DOI: 10.1021/ja038159+] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The bacterial exotoxins, cholera toxin (CT), pertussis toxin (PT), and diphtheria toxin (DT), interfere with specific host proteins to cause tissue damage for their respective infections. The common toxic mechanism for these agents is mono-ADP-ribosylation of specific amino acids in G(s)(alpha), G(i)(alpha), and eEF-2 proteins, respectively, by the catalytic A chains of the toxins (CTA, PTA, and DTA). In the absence of acceptor proteins, these toxins also act as NAD(+)-N-ribosyl hydrolases. The transition-state structures for NAD(+) hydrolysis and ADP-ribosylation reactions have oxacarbenium ion character in the ribose. We designed and synthesized analogues of NAD(+) to resemble their oxacarbenium ion transition states. Inhibitors with oxacarbenium mimics replacing the NMN-ribosyl group of NAD(+) show 200-620-fold increased affinity in the hydrolytic and N-ribosyl transferase reactions catalyzed by CTA. These analogues are also inhibitors for the hydrolysis of NAD(+) by PTA with K(i) values of 24-40 microM, but bind with similar affinity to the NAD(+) substrates. Inhibition of the NAD(+) hydrolysis and ADP-ribosyl transferase reactions of DTA gave K(i) values from 19 to 48 microM. Catalytic rate enhancements by the bacterial exotoxins are small, and thus transition-state analogues cannot capture large energies of activation. In the cases of DTA and PTA, analogues known to resemble the transition states bind with approximately the same affinity as substrates. Transition-state analogue interrogation of the bacterial toxins indicates that CTA gains catalytic efficiency from modest transition-state stabilization, but DTA and PTA catalyze ADP-ribosyl transferase reactions more from ground-state destabilization. pH dependence of inhibitor action indicated that both neutral and cationic forms of transition-state analogues bind to DTA with similar affinity. The origin of this similarity is proposed to reside in the cationic nature of NAD(+) both as substrate and at the transition state.
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Affiliation(s)
- Guo-Chun Zhou
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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10
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Abstract
Cholera toxin (CT) is responsible for the major pathological features of cholera, but in addition to its cytotoxic properties, CT is a potent mucosal adjuvant when coadministered with antigens at mucosal sites. Discovery of CT adjuvanticity has prompted the generation of CT chimeras with reduced toxicity and improved efficiency for antigen presentation at mucosal sites. To date, chimeric forms of CT have been produced in bacterial strains by coexpressing the CT B subunit and a chimeric form of the CT A subunit consisting of a target protein antigen fused with the A2 polypeptide of CT. In this study, a chimeric protein consisting of green fluorescent protein (GFP) fused with polypeptide A2 was generated to investigate the feasibility of assembling CT holotoxin-like complexes in vitro. The assembly of such holotoxin-like complexes would expand the variety of antigenic compounds that could be incorporated into CT-based vaccines. In this study, GFP-A2/CTB complexes could be generated in vitro using a stepwise denaturation-renaturation process. These findings suggest that it is possible to generate novel mucosal vaccines consisting of macromolecules that are chemically coupled to polypeptide A2 and reconstituted into CT-like complexes in vitro.
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Affiliation(s)
- S O Hatic
- Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas 66045, USA
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11
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Jobling MG, Holmes RK. Biological and biochemical characterization of variant A subunits of cholera toxin constructed by site-directed mutagenesis. J Bacteriol 2001; 183:4024-32. [PMID: 11395467 PMCID: PMC95286 DOI: 10.1128/jb.183.13.4024-4032.2001] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Cholera toxin (CT) is the prototype for the Vibrio cholerae-Escherichia coli family of heat-labile enterotoxins having an AB5 structure. By substituting amino acids in the enzymatic A subunit that are highly conserved in all members of this family, we constructed 23 variants of CT that exhibited decreased or undetectable toxicity and we characterized their biological and biochemical properties. Many variants exhibited previously undescribed temperature-sensitive assembly of holotoxin and/or increased sensitivity to proteolysis, which in all cases correlated with exposure of epitopes of CT-A that are normally hidden in native CT holotoxin. Substitutions within and deletion of the entire active-site-occluding loop demonstrated a prominent role for His-44 and this loop in the structure and activity of CT. Several novel variants with wild-type assembly and stability showed significantly decreased toxicity and enzymatic activity (e.g., variants at positions R11, I16, R25, E29, and S68+V72). In most variants the reduction in toxicity was proportional to the decrease in enzymatic activity. For substitutions or insertions at E29 and Y30 the decrease in toxicity was 10- and 5-fold more than the reduction in enzymatic activity, but for variants with R25G, E110D, or E112D substitutions the decrease in enzymatic activity was 12- to 50-fold more than the reduction in toxicity. These variants may be useful as tools for additional studies on the cell biology of toxin action and/or as attenuated toxins for adjuvant or vaccine use.
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Affiliation(s)
- M G Jobling
- Department of Microbiology, University of Colorado Health Sciences Center, Denver, Colorado 80220, USA
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12
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Ma Y, Ludden PW. Role of the dinitrogenase reductase arginine 101 residue in dinitrogenase reductase ADP-ribosyltransferase binding, NAD binding, and cleavage. J Bacteriol 2001; 183:250-6. [PMID: 11114923 PMCID: PMC94872 DOI: 10.1128/jb.183.1.250-256.2001] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Dinitrogenase reductase is posttranslationally regulated by dinitrogenase reductase ADP-ribosyltransferase (DRAT) via ADP-ribosylation of the arginine 101 residue in some bacteria. Rhodospirillum rubrum strains in which the arginine 101 of dinitrogenase reductase was replaced by tyrosine, phenylalanine, or leucine were constructed by site-directed mutagenesis of the nifH gene. The strain containing the R101F form of dinitrogenase reductase retains 91%, the strain containing the R101Y form retains 72%, and the strain containing the R101L form retains only 28% of in vivo nitrogenase activity of the strain containing the dinitrogenase reductase with arginine at position 101. In vivo acetylene reduction assays, immunoblotting with anti-dinitrogenase reductase antibody, and [adenylate-(32)P]NAD labeling experiments showed that no switch-off of nitrogenase activity occurred in any of the three mutants and no ADP-ribosylation of altered dinitrogenase reductases occurred either in vivo or in vitro. Altered dinitrogenase reductases from strains UR629 (R101Y) and UR630 (R101F) were purified to homogeneity. The R101F and R101Y forms of dinitrogenase reductase were able to form a complex with DRAT that could be chemically cross-linked by 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide. The R101F form of dinitrogenase reductase and DRAT together were not able to cleave NAD. This suggests that arginine 101 is not critical for the binding of DRAT to dinitrogenase reductase but that the availability of arginine 101 is important for NAD cleavage. Both DRAT and dinitrogenase reductase can be labeled by [carbonyl-(14)C]NAD individually upon UV irradiation, but most (14)C label is incorporated into DRAT when both proteins are present. The ability of R101F dinitrogenase reductase to be labeled by [carbonyl-(14)C]NAD suggested that Arg 101 is not absolutely required for NAD binding.
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Affiliation(s)
- Y Ma
- Department of Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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13
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Jobling MG, Holmes RK. Identification of motifs in cholera toxin A1 polypeptide that are required for its interaction with human ADP-ribosylation factor 6 in a bacterial two-hybrid system. Proc Natl Acad Sci U S A 2000; 97:14662-7. [PMID: 11106366 PMCID: PMC18975 DOI: 10.1073/pnas.011442598] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The latent ADP-ribosyltransferase activity of cholera toxin (CT) that is activated after proteolytic nicking and reduction is associated with the CT A1 subunit (CTA1) polypeptide. This activity is stimulated in vitro by interaction with eukaryotic proteins termed ADP-ribosylation factors (ARFs). We analyzed this interaction in a modified bacterial two-hybrid system in which the T18 and T25 fragments of the catalytic domain of Bordetella pertussis adenylate cyclase were fused to CTA1 and human ARF6 polypeptides, respectively. Direct interaction between the CTA1 and ARF6 domains in these hybrid proteins reconstituted the adenylate cyclase activity and permitted cAMP-dependent signal transduction in an Escherichia coli reporter system. We constructed improved vectors and reporter strains for this system, and we isolated variants of CTA1 that showed greatly decreased ability to interact with ARF6. Amino acid substitutions in these CTA1 variants were widely separated in the primary sequence but were contiguous in the three-dimensional structure of CT. These residues, which begin to define the ARF interaction motif of CTA1, are partially buried in the crystal structure of CT holotoxin, suggesting that a change in the conformation of CTA1 enables it to bind to ARF. Variant CTA polypeptides containing these substitutions assembled into holotoxin as well as wild-type CTA, but the variant holotoxins showed greatly reduced enterotoxicity. These findings suggest functional interaction between CTA1 and ARF is required for maximal toxicity of CT in vivo.
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Affiliation(s)
- M G Jobling
- Department of Microbiology, University of Colorado Health Sciences Center, Denver, CO 80220, USA
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14
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McCann JA, Mertz JA, Czworkowski J, Picking WD. Conformational changes in cholera toxin B subunit-ganglioside GM1 complexes are elicited by environmental pH and evoke changes in membrane structure. Biochemistry 1997; 36:9169-78. [PMID: 9230049 DOI: 10.1021/bi962996p] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Fluorescence resonance energy transfer (FRET) was used to monitor pH-dependent structural changes in the cholera toxin B subunit (CTB) and the membranes with which CTB associates. The distance separating the single tryptophan (Trp88) of each CTB monomer and a pyrene probe linked to the membrane-imbedded tail of ganglioside GM1 is not influenced by pH in a range from 3.5 to 7.5, consistent with the position of Trp88 in the GM1 binding site of CTB. In contrast, the distance between the pyrene probe on GM1 and coumarin, stilbene, or fluorescein probes covalently linked to specific sites on CTB appears to increase significantly as the pH is lowered to 5.0 or less. This conformational change is not accompanied by detectable changes in the distance between Trp88 and these extrinsic probe positions in the presence of nonfluorescent GM1. However, when the distance from Trp88 to the extrinsic probes is monitored as a function of pH in the absence of GM1, a conformational change is seen which indicates that receptor binding influences the character of pH-dependent conformational changes that occur within CTB. Interestingly, the observed change in CTB conformation is accompanied by a change in the relative position of GM1 within the membrane as judged by FRET from the pyrene probe on GM1 to a 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) probe linked to the polar head group of phosphatidylethanolamine and positioned at the membrane surface. Taken together, the data imply that low endosomal pH is capable of inducing structural changes in CTB, which, in turn, exert effects on the structure of the membrane to which CTB is bound. These phenomena may have a role in (1) processing of cholera toxin within the endosomal compartments of some target cell types, (2) determining the lag time between cholera toxin binding and the target cell response to cholera intoxication, or (3) the efficiency of CTB and cholera toxin as mucosal adjuvants.
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Affiliation(s)
- J A McCann
- Department of Biology, Saint Louis University, St. Louis, Missouri 63103-2010, USA
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15
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Rising KA, Schramm VL. Transition State Analysis of NAD+ Hydrolysis by the Cholera Toxin Catalytic Subunit. J Am Chem Soc 1997. [DOI: 10.1021/ja9621915] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Kathleen A. Rising
- Contribution from the Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461
| | - Vern L. Schramm
- Contribution from the Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461
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16
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Bastiaens PI, Majoul IV, Verveer PJ, Söling HD, Jovin TM. Imaging the intracellular trafficking and state of the AB5 quaternary structure of cholera toxin. EMBO J 1996; 15:4246-53. [PMID: 8861953 PMCID: PMC452150] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The subcellular localization and corresponding quaternary state of fluorescent labelled cholera toxin were determined at different time points after exposure to living cells by a novel form of fluorescence confocal microscopy. The compartmentalization and locus of separation of the pentameric B subunits (CTB) from the A subunit (CTA) of the toxin were evaluated on a pixel-by-pixel (voxel-by-voxel) basis by measuring the fluorescence resonance energy transfer (FRET) between CTB labelled with the sulfoindocyanine dye Cy3 and an antibody against CTA labelled with Cy5. The FRET efficiency was determined by a new technique based on the release of quenching of the Cy3 donor after photodestruction of the Cy5 acceptor in a region of interest within the cell. The results demonstrate vesicular transport of the holotoxin from the plasma membrane to the Golgi compartment with subsequent separation of the CTA and CTB subunits. The CTA subunit is redirected to the plasma membrane by retrograde transport via the endoplasmic reticulum whereas the CTB subunit persists in the Golgi compartment.
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Affiliation(s)
- P I Bastiaens
- Department of Molecular Biology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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17
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Aleo MF, Sestini S, Pompucci G, Preti A. Enzymatic activities affecting exogenous nicotinamide adenine dinucleotide in human skin fibroblasts. J Cell Physiol 1996; 167:173-6. [PMID: 8698835 DOI: 10.1002/(sici)1097-4652(199604)167:1<173::aid-jcp20>3.0.co;2-b] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The fate of nicotinamide adenine dinucleotide (NAD), AMP, and ADP-ribose supplied to intact human skin fibroblasts was monitored, and the concentrations of intra- and extracellular pyridine and purine compounds were determined by HPLC analysis. Two enzymatic activities affecting extracellular NAD were detected on the plasma membrane, one hydrolyzing the pyrophosphoric bond and yielding nicotinamide mononucleotide (nucleotide pyrophosphatase) and the other cleaving the glycoside link and releasing nicotinamide (NAD-glycohydrolase). No AMP or ADP-ribose was found in the extracellular medium of cells incubated with NAD, the former being completely catabolized to hypoxanthine and the latter degraded to adenine and hypoxanthine.
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Affiliation(s)
- M F Aleo
- Department of Biomedical Sciences and Biotechnology, University of Brescia, Italy
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18
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van den Akker F, Merritt EA, Pizza M, Domenighini M, Rappuoli R, Hol WG. The Arg7Lys mutant of heat-labile enterotoxin exhibits great flexibility of active site loop 47-56 of the A subunit. Biochemistry 1995; 34:10996-1004. [PMID: 7669757 DOI: 10.1021/bi00035a005] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The heat-labile enterotoxin from Escherichia coli (LT) is a member of the cholera toxin family. These and other members of the larger class of AB5 bacterial toxins act through catalyzing the ADP-ribosylation of various intracellular targets including Gs alpha. The A subunit is responsible for this covalent modification, while the B pentamer is involved in receptor recognition. We report here the crystal structure of an inactive single-site mutant of LT in which arginine 7 of the A subunit has been replaced by a lysine residue. The final model contains 103 residues for each of the five B subunits, 175 residues for the A1 subunit, and 41 residues for the A2 subunit. In this Arg7Lys structure the active site cleft within the A subunit is wider by approximately 1 A than is seen in the wild-type LT. Furthermore, a loop near the active site consisting of residues 47-56 is disordered in the Arg7Lys structure, even though the new lysine residue at position 7 assumes a position which virtually coincides with that of Arg7 in the wild-type structure. The displacement of residues 47-56 as seen in the mutant structure is proposed to be necessary for allowing NAD access to the active site of the wild-type LT. On the basis of the differences observed between the wild-type and Arg7Lys structures, we propose a model for a coordinated sequence of conformational changes required for full activation of LT upon reduction of disulfide bridge 187-199 and cleavage of the peptide loop between the two cysteines in the A subunit.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- F van den Akker
- Department of Biological Structure and Biochemistry, University of Washington, Seattle, USA
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19
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Spangler BD. Structure and function of cholera toxin and the related Escherichia coli heat-labile enterotoxin. Microbiol Rev 1992; 56:622-47. [PMID: 1480112 PMCID: PMC372891 DOI: 10.1128/mr.56.4.622-647.1992] [Citation(s) in RCA: 422] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Cholera and the related Escherichia coli-associated diarrheal disease are important problems confronting Third World nations and any area where water supplies can become contaminated. The disease is extremely debilitating and may be fatal in the absence of treatment. Symptoms are caused by the action of cholera toxin, secreted by the bacterium Vibrio cholerae, or by a closely related heat-labile enterotoxin, produced by Escherichia coli, that causes a milder, more common traveler's diarrhea. Both toxins bind receptors in intestinal epithelial cells and insert an enzymatic subunit that modifies a G protein associated with the adenylate cyclase complex. The consequent stimulated production of cyclic AMP, or other factors such as increased synthesis of prostaglandins by intoxicated cells, initiates a metabolic cascade that results in the excessive secretion of fluid and electrolytes characteristic of the disease. The toxins have a very high degree of structural and functional homology and may be evolutionarily related. Several effective new vaccine formulations have been developed and tested, and a growing family of endogenous cofactors is being discovered in eukaryotic cells. The recent elucidation of the three-dimensional structure of the heat-labile enterotoxin has provided an opportunity to examine and compare the correlations between structure and function of the two toxins. This information may improve our understanding of the disease process itself, as well as illuminate the role of the toxin in studies of signal transduction and G-protein function.
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Affiliation(s)
- B D Spangler
- Biological and Medical Research Division, Argonne National Laboratory, Illinois 60439
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20
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Sixma TK, Pronk SE, Kalk KH, Wartna ES, van Zanten BA, Witholt B, Hol WG. Crystal structure of a cholera toxin-related heat-labile enterotoxin from E. coli. Nature 1991; 351:371-7. [PMID: 2034287 DOI: 10.1038/351371a0] [Citation(s) in RCA: 386] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Examination of the structure of Escherichia coli heat-labile enterotoxin in the AB5 complex at a resolution of 2.3A reveals that the doughnut-shaped B pentamer binds the enzymatic A subunit using a hairpin of the A2 fragment, through a highly charged central pore. Putative ganglioside GM1-binding sites on the B subunits are more than 20A removed from the membrane-crossing A1 subunit. This ADP-ribosylating (A1) fragment of the toxin has structural homology with the catalytic region of exotoxin A and hence also to diphtheria toxin.
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Affiliation(s)
- T K Sixma
- BIOSON Research Institute, Groningen, The Netherlands
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21
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Domenighini M, Montecucco C, Ripka WC, Rappuoli R. Computer modelling of the NAD binding site of ADP-ribosylating toxins: active-site structure and mechanism of NAD binding. Mol Microbiol 1991; 5:23-31. [PMID: 1901617 DOI: 10.1111/j.1365-2958.1991.tb01822.x] [Citation(s) in RCA: 64] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Five ADP-ribosylating bacterial toxins, pertussis toxin, cholera toxin, diphtheria toxin, Escherichia LT toxin and Pseudomonas exotoxin A, show significant homology in selected segments of their sequence. Site-directed mutagenesis and chemical modification of residues within these regions cause loss of catalytic activity and of NAD binding. On the basis of these results and of molecular modelling based on the three-dimensional structure of exotoxin A, the geometry of an NAD binding site common to all the toxins is deduced and described in the paper. For diphtheria toxin, sequence similarity with exotoxin A is such that its preliminary structure can be computed by molecular modelling, whereas for the other toxins similarity appears to be restricted to the NAD binding site. Moreover, an analysis of molecular fitting of the NAD molecule into its binding cavity suggests a new model for the conformation of the bound NAD that better accounts for all available experimental information.
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22
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Slama JT, Simmons AM. Inhibition of NAD glycohydrolase and ADP-ribosyl transferases by carbocyclic analogues of oxidized nicotinamide adenine dinucleotide. Biochemistry 1989; 28:7688-94. [PMID: 2532931 DOI: 10.1021/bi00445a025] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Analogues of oxidized nicotinamide adenine dinucleotide (NAD+) in which a 2,3-dihydroxycyclopentane ring replaces the beta-D-ribonucleotide ring of the nicotinamide riboside moiety of NAD+ have recently been synthesized [Slama, J. T., & Simmons, A. M. (1988) Biochemistry 27, 183]. Carbocyclic NAD+ analogues have been shown to inhibit NAD glycohydrolases and ADP-ribosyl transferases such as cholera toxin A subunit. In this study, the diastereomeric mixture of dinucleotides was separated, and the inhibitory capacity of each of the purified diastereomers was defined. The NAD+ analogue in which the D-dihydroxycyclopentane is substituted for the D-ribose is designated carba-NAD and was demonstrated to be a poor inhibitor of the Bungarus fasciatus venom NAD glycohydrolase. The diastereomeric dinucleotide pseudo-carbocyclic-NAD (psi-carba-NAD), containing L-dihydroxycyclopentane in place of the D-ribose of NAD+, was shown, however, to be a potent competitive inhibitor of the venom NAD glycohydrolase with an inhibitor dissociation constant (Ki) of 35 microM. This was surprising since psi-carba-NAD contains the carbocyclic analogue of the unnatural L-ribotide and was therefore expected to be a biologically inactive diastereomer. psi-Carba-NAD also competitively inhibited the insoluble brain NAD glycohydrolase from cow (Ki = 6.7 microM) and sheep (Ki = 31 microM) enzyme against which carba-NAD is ineffective. Sensitivity to psi-carba-NAD was found to parallel sensitivity to inhibition by isonicotinic acid hydrazide, another NADase inhibitor. psi-Carba-NAD is neither a substrate for nor an inhibitor of alcohol dehydrogenase, whereas carba-NAD is an efficient dehydrogenase substrate.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- J T Slama
- Department of Biochemistry, University of Texas Health Science Center, San Antonio 78284-7760
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