scholarly journals Agrobacterium tumefaciens VirB6 Protein Participates in Formation of VirB7 and VirB9 Complexes Required for Type IV Secretion

2003 ◽  
Vol 185 (9) ◽  
pp. 2867-2878 ◽  
Author(s):  
Simon J. Jakubowski ◽  
Vidhya Krishnamoorthy ◽  
Peter J. Christie
Keyword(s):  
Agrobacterium Tumefaciens ◽  
Protein Complexes ◽  
Polyacrylamide Gel Electrophoresis ◽  
Sodium Dodecyl ◽  
Type Iv Secretion ◽  
Wild Type ◽  
Mutant Proteins ◽  
Type Iv ◽  
Inner Membrane Protein ◽  
Substrate Transfer

ABSTRACT This study characterized the contribution of Agrobacterium tumefaciens VirB6, a polytopic inner membrane protein, to the formation of outer membrane VirB7 lipoprotein and VirB9 protein multimers required for type IV secretion. VirB7 assembles as a disulfide cross-linked homodimer that associates with the T pilus and a VirB7-VirB9 heterodimer that stabilizes other VirB proteins during biogenesis of the secretion machine. Two presumptive VirB protein complexes, composed of VirB6, VirB7, and VirB9 and of VirB7, VirB9, and VirB10, were isolated by immunoprecipitation or glutathione S-transferase pulldown assays from detergent-solubilized membrane extracts of wild-type A348 and a strain producing only VirB6 through VirB10 among the VirB proteins. To examine the biological importance of VirB6 complex formation for type IV secretion, we monitored the effects of nonstoichiometric VirB6 production and the synthesis of VirB6 derivatives with 4-residue insertions (VirB6.i4) on VirB7 and VirB9 multimerization, T-pilus assembly, and substrate transfer. A virB6 gene deletion mutant accumulated VirB7 dimers at diminished steady-state levels, whereas complementation with a plasmid bearing wild-type virB6 partially restored accumulation of the dimers. VirB6 overproduction was correlated with formation of higher-order VirB9 complexes or aggregates and also blocked substrate transfer without a detectable disruption of T-pilus production; these phenotypes were displayed by cells grown at 28°C, a temperature that favors VirB protein turnover, but not by cells grown at 20°C. Strains producing several VirB6.i4 mutant proteins assembled novel VirB7 and VirB9 complexes detectable by nonreducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and two strains producing the D60.i4 and L191.i4 mutant proteins translocated IncQ plasmid and VirE2 effector protein substrates in the absence of a detectable T pilus. Our findings support a model that VirB6 mediates formation of VirB7 and VirB9 complexes required for biogenesis of the T pilus and the secretion channel.

scholarly journals Agrobacterium tumefaciens Twin-Arginine-Dependent Translocation Is Important for Virulence, Flagellation, and Chemotaxis but Not Type IV Secretion

2003 ◽  
Vol 185 (3) ◽  
pp. 760-771 ◽  
Author(s):  
Zhiyong Ding ◽  
Peter J. Christie
Keyword(s):  
Agrobacterium Tumefaciens ◽  
Type Iv Secretion ◽  
Anaerobic Growth ◽  
Induction Medium ◽  
Rich Medium ◽  
Wild Type ◽  
Prolonged Incubation ◽  
Type Iv ◽  
Tat System ◽  
Mutant Cells

ABSTRACT This study characterized the contribution of the twin-arginine translocation (TAT) pathway to growth, motility, and virulence of the phytopathogen Agrobacterium tumefaciens. In contrast to wild-type strain A348, a tatC null mutant failed to export the green fluorescent protein fused to the trimethylamine N-oxide reductase (TorA) signal sequence or to grow on nitrate as a sole electron acceptor during anaerobic growth. The tatC mutant displayed defects in growth rate and cell division but not in cell viability, and it also released abundant levels of several proteins into the culture supernatant when grown in rich medium or in vir induction minimal medium. Nearly all A348 cells were highly motile in both rich and minimal media. By contrast, approximately 0.1% of the tatC mutant cells were motile in rich medium, and <0.01% were motile in vir induction medium. Nonmotile tatC mutant cells lacked detectable flagella, whereas motile tatC mutant cells collected from the edge of a motility halo possessed flagella but not because of reversion to a functional TAT system. Motile tatC cells failed to exhibit chemotaxis toward sugars under aerobic conditions or towards nitrate under anaerobic conditions. The tatC mutant was highly attenuated for virulence, only occasionally (∼15% of inoculations) inciting formation of small tumors on plants after a prolonged incubation period of 6 to 8 weeks. However, an enriched subpopulation of motile tatC mutants exhibited enhanced virulence compared to the nonmotile variants. Finally, the tatC mutant transferred T-DNA and protein effectors to plant cells and a mobilizable IncQ plasmid to agrobacterial recipients at wild-type levels. Together, our findings establish that, in addition to its role in secretion of folded cofactor-bound enzymes functioning in alternative respiration, the TAT system of A. tumefaciens is an important virulence determinant. Furthermore, this secretion pathway contributes to flagellar biogenesis and chemotactic responses but not to sensory perception of plant signals or the assembly of a type IV secretion system.

scholarly journals General Mutagenesis of F Plasmid TraI Reveals Its Role in Conjugative Regulation

2006 ◽  
Vol 188 (17) ◽  
pp. 6346-6353 ◽  
Author(s):  
Rembrandt J. F. Haft ◽  
Gilberto Palacios ◽  
Tran Nguyen ◽  
Manuela Mally ◽  
Eliora G. Gachelet ◽  
...  
Keyword(s):  
Type Iv Secretion ◽  
Dominant Negative ◽  
Wild Type ◽  
F Plasmid ◽  
Phenotypic Analysis ◽  
Mutant Proteins ◽  
Catalytic Domains ◽  
Type Iv ◽  
Negative Regulatory Role

ABSTRACT Bacteria commonly exchange genetic information by the horizontal transfer of conjugative plasmids. In gram-negative conjugation, a relaxase enzyme is absolutely required to prepare plasmid DNA for transit into the recipient via a type IV secretion system. Here we report a mutagenesis of the F plasmid relaxase gene traI using in-frame, 31-codon insertions. Phenotypic analysis of our mutant library revealed that several mutant proteins are functional in conjugation, highlighting regions of TraI that can tolerate insertions of a moderate size. We also demonstrate that wild-type TraI, when overexpressed, plays a dominant-negative regulatory role in conjugation, repressing plasmid transfer frequencies ∼100-fold. Mutant TraI proteins with insertions in a region of approximately 400 residues between the consensus relaxase and helicase sequences did not cause conjugative repression. These unrestrictive TraI variants have normal relaxase activity in vivo, and several have wild-type conjugative functions when expressed at normal levels. We postulate that TraI negatively regulates conjugation by interacting with and sequestering some component of the conjugative apparatus. Our data indicate that the domain responsible for conjugative repression resides in the central region of TraI between the protein's catalytic domains.

scholarly journals VirB6 Is Required for Stabilization of VirB5 and VirB3 and Formation of VirB7 Homodimers in Agrobacterium tumefaciens

2000 ◽  
Vol 182 (16) ◽  
pp. 4505-4511 ◽  
Author(s):  
Siegfried Hapfelmeier ◽  
Natalie Domke ◽  
Patricia C. Zambryski ◽  
Christian Baron
Keyword(s):  
Agrobacterium Tumefaciens ◽  
Sequence Similarity ◽  
Genetic Material ◽  
Direct Interaction ◽  
Minor Component ◽  
Wild Type ◽  
Protein Levels ◽  
Type Iv ◽  
Assembly Factor ◽  
Inner Membrane Protein

ABSTRACT VirB6 from Agrobacterium tumefaciens is an essential component of the type IV secretion machinery for T pilus formation and genetic transformation of plants. Due to its predicted topology as a polytopic inner membrane protein, it was proposed to form the transport pore for cell-to-cell transfer of genetic material and proteinaceous virulence factors. Here, we show that the absence of VirB6 leads to reduced cellular levels of VirB5 and VirB3, which were proposed to assist T pilus formation as minor component(s) or assembly factor(s), respectively. Overexpression ofvirB6 in trans restored levels of cell-bound and T pilus-associated VirB5 to wild type but did not restore VirB3 levels. Thus, VirB6 has a stabilizing effect on VirB5 accumulation, thereby regulating T pilus assembly. In the absence of VirB6, cell-bound VirB7 monomers and VirB7-VirB9 heterodimers were reduced and VirB7 homodimer formation was abolished. This effect could not be restored by expression of VirB6 in trans. Expression of TraD, a component of the transfer machinery of the IncN plasmid pKM101, with significant sequence similarity to VirB6, restored neither protein levels nor bacterial virulence but partly permitted T pilus formation in a virB6 deletion strain. VirB6 may therefore regulate T pilus formation by direct interaction with VirB5, and wild-type levels of VirB3 and VirB7 homodimers are not required.

scholarly journals Nonspecific Adherence and Fibril Biogenesis by Actinobacillus actinomycetemcomitans: TadA Protein Is an ATPase

2001 ◽  
Vol 183 (20) ◽  
pp. 5927-5936 ◽  
Author(s):  
Mrinal K. Bhattacharjee ◽  
Scott C. Kachlany ◽  
Daniel H. Fine ◽  
David H. Figurski
Keyword(s):  
Atpase Activity ◽  
Transmembrane Domain ◽  
Polyacrylamide Gel Electrophoresis ◽  
Sodium Dodecyl ◽  
Nucleotide Binding ◽  
Type Iv Secretion ◽  
Actinobacillus Actinomycetemcomitans ◽  
Predicted Amino Acid Sequence ◽  
Inner Membrane ◽  
Type Iv

ABSTRACT Cells of Actinobacillus actinomycetemcomitans, a gram-negative pathogen responsible for an aggressive form of juvenile periodontitis, form tenaciously adherent biofilms on solid surfaces. The bacteria produce long fibrils of bundled pili, which are required for adherence. Mutations in flp-1, which encodes the major subunit of the pili, or any of seven downstreamtad genes (tadABCDEFG) cause defects in fibril production, autoaggregation, and tenacious adherence. We proposed that the tad genes specify part of a novel secretion system for the assembly and transport of Flp pili. The predicted amino acid sequence of TadA (426 amino acids, 47,140 Da) contains motifs for nucleotide binding and hydrolysis common among secretion NTP hydrolase (NTPase) proteins. In addition, thetadA gene is the first representative of a distinct subfamily of potential type IV secretion NTPase genes. Here we report studies on the function of TadA. The tadA gene was altered to express a modified version of TadA that has the 11-residue epitope (T7-TAG) fused to its C terminus. The TadA-T7 protein was indistinguishable from the wild type in its ability to complement the fibril and adherence defects of A. actinomycetemcomitanstadA mutants. Although TadA is not predicted to have a transmembrane domain, the protein was localized to the inner membrane and cytoplasmic fractions of A. actinomycetemcomitans cells, indicating a possible peripheral association with the inner membrane. TadA-T7 was purified and found to hydrolyze ATP in vitro. The ATPase activity is stimulated by Triton X-100, with maximal stimulation at the critical micellar concentration. TadA-T7 forms multimers that are stable during sodium dodecyl sulfate-polyacrylamide gel electrophoresis in nonreducing conditions, and electron microscopy revealed that TadA-T7 can form structures closely resembling the hexameric rings of other type IV secretion NTPases. Site-directed mutagenesis was used to substitute Ala and Gln residues for the conserved Lys residue of the Walker A box for nucleotide binding. Both mutants were found to be defective in their ability to complementtadA mutants. We suggest that the ATPase activity of TadA is required to energize the assembly or secretion of Flp pili for tight adherence of A. actinomycetemcomitans.

Identification of pilin pools in the membranes of Pseudomonas aeruginosa

1982 ◽  
Vol 152 (2) ◽  
pp. 687-691
Author(s):  
T H Watts ◽  
E A Worobec ◽  
W Paranchych
Keyword(s):  
Staphylococcus Aureus ◽  
Pseudomonas Aeruginosa ◽  
Gel Electrophoresis ◽  
Type Strain ◽  
Wild Type Strain ◽  
Polyacrylamide Gel Electrophoresis ◽  
Protein A ◽  
Sodium Dodecyl ◽  
Wild Type ◽  
Outer Membranes

The proteins of purified inner and outer membranes obtained from Pseudomonas aeruginosa strains PAK and PAK/2Pfs were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, transferred to nitrocellulose, and treated with antiserum raised against pure pili. Bound antipilus antibodies were visualized by reaction with 125I-labeled protein A from Staphylococcus aureus. The results showed that there are pools of pilin in both the inner and outer membranes of P. aeruginosa and that the pool size in the multipiliated strain is comparable with that of the wild-type strain.

Novel Catalatic Proteins of Bakers' Yeast. I. An Atypical Catalase

1973 ◽  
Vol 51 (11) ◽  
pp. 1551-1555 ◽  
Author(s):  
Tony C. M. Seah ◽  
A. R. Bhatti ◽  
J. G. Kaplan
Keyword(s):  
Molecular Weight ◽  
Gel Electrophoresis ◽  
Specific Activity ◽  
Polyacrylamide Gel Electrophoresis ◽  
Sodium Dodecyl ◽  
Native Protein ◽  
Wild Type ◽  
Major Band ◽  
Subunit Molecular Weight ◽  
Purification And Properties

At any stage of growth of a wild-type bakers' yeast, some 20% of the catalatic activity of crude extracts is not precipitable by means of antibody prepared against the typical catalase (catalase T), whose purification and properties have been previously described. Some of this catalatic activity is due to the presence of an atypical catalase (catalase A), a heme protein, with a molecular weight estimated as 170 000 – 190 000, considerably lower than that of the usual catalases (225 000 – 250 000). Preparations of catalase A were found to be homogeneous in the analytical ultracentrifuge and in polyacrylamide gel electrophoresis. Its subunit molecular weight, determined from its iron content, was 46 500, virtually the same as that of the major band obtained in gel electrophoresis in the presence of sodium dodecyl sulfate, suggesting that the native protein is tetrameric. Its specific activity is in the range of those reported for other typical catalases.

scholarly journals The Helicobacter pylori Autotransporter ImaA Tempers the Bacterium's Interaction with α5β1 Integrin

2016 ◽  
Vol 85 (1) ◽  
Author(s):  
William E. Sause ◽  
Daniela Keilberg ◽  
Soufiane Aboulhouda ◽  
Karen M. Ottemann
Keyword(s):  
Helicobacter Pylori ◽  
Host Cell ◽  
Type Iv Secretion ◽  
Host Cells ◽  
Wild Type ◽  
Content Type ◽  
Type Iv ◽  
H Pylori ◽  
Α5β1 Integrin ◽  
Cell Interface

ABSTRACT The human pathogen Helicobacter pylori uses the host receptor α5β1 integrin to trigger inflammation in host cells via its cag pathogenicity island (cag PAI) type IV secretion system (T4SS). Here, we report that the H. pylori ImaA protein (HP0289) decreases the action of the cag PAI T4SS via tempering the bacterium's interaction with α5β1 integrin. Previously, imaA-null mutants were found to induce an elevated inflammatory response that was dependent on the cag PAI T4SS; here we extend those findings to show that the elevated response is independent of the CagA effector protein. To understand how ImaA could be affecting cag PAI T4SS activity at the host cell interface, we utilized the Phyre structural threading program and found that ImaA has a region with remote homology to bacterial integrin-binding proteins. This region was required for ImaA function. Unexpectedly, we observed that imaA mutants bound higher levels of α5β1 integrin than wild-type H. pylori, an outcome that required the predicted integrin-binding homology region of ImaA. Lastly, we report that ImaA directly affected the amount of host cell β1 integrin but not other cellular integrins. Our results thus suggest a model in which H. pylori employs ImaA to regulate interactions between integrin and the T4SS and thus alter the host inflammatory strength.

Regulation of alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (AldDH) in Aspergillus nidulans

1983 ◽  
Vol 217 (1208) ◽  
pp. 243-264 ◽  
Keyword(s):  
Alcohol Dehydrogenase ◽  
Aspergillus Nidulans ◽  
Structural Gene ◽  
Aldehyde Dehydrogenase ◽  
Gel Electrophoresis ◽  
Regulatory Gene ◽  
Polyacrylamide Gel Electrophoresis ◽  
Sodium Dodecyl ◽  
Wild Type ◽  
Cell Extracts

There is a single major alcohol dehydrogenase (ADH) and a single major aldehyde dehydrogenase (AldDH) in Aspergillus nidulans . Both ADH and AldDH are induced by ethanol and by acetaldehyde and both are subject to carbon catabolite repression. ADH and AldDH are necessary for the utilization of ethanol and of threonine, indicating that both compounds are utilized via acetaldehyde. ADH and AldDH each give a single major activity band on gel electrophoresis. Sodium dodecyl sulphate polyacrylamide gel electrophoresis of cell extracts shows at least two similar ADH polypeptides of approximate relative molecular mass (r. m. m.) 41000 and two similar AldDH polypeptides of approximate r. m. m. 57000. The in vitro translation of mRNA from induced, carbon derepressed wild-type cells gives up to three ADH polypeptides in the r. m. m. range 39000-43000 and an AldDH polypeptide of approximate r. m. m. 57000. The mRNA from uninduced, carbon repressed wild-type cells does not direct the synthesis of the ADH and AldDH polypeptides. This indicates that the regulation of ADH and AldDH is at the level of transcription and/or post-transcriptional modification. The probable explanation of the multiple ADH polypeptides is post-transcriptional modification of the mRNA. Allyl alcohol mutants were made by using diepoxyoctane and γ-rays as mutagens. There are two classes, alcA and alcR . Neither class can utilize ethanol or threonine as a carbon source. The alcA mutants lack normal ADH and are recessive. Of the 47 alcA mutants examined 39 do not make the ADH polypeptides while eight do so. Therefore alcA is the structural gene for ADH. The two alcA mutants tested do not make functional mRNA for ADH. The alcR mutants lack both ADH and AldDH and are recessive. No alcR mutants make the ADH or the AldDH polypeptides. The three alcR mutants tested do not make functional ADH or AldDH mRNA. The mutant alcR 125 is a nonsense mutant, which establishes that alcR codes for a protein. The alcA and alcR genes are adjacent on chromosome VII and a preliminary fine-structure map of the alcA gene has been made. Three mutants that cannot utilize ethanol or threonine and have ADH, but lack AldDH, define a gene AldA on chromosome VIII. The aldA 23 mutant makes the AldDH polypeptides, the other two aldA mutants do not. Therefore aldA is probably the structural gene for AldDH. Our current hypothesis is that alcA and aldA are the structural genes for ADH and AldDH respectively and alcR is a transacting regulatory gene coding for a protein whose function is necessary for the expression of the alcA and aldA genes.

scholarly journals The Spirochete FlaA Periplasmic Flagellar Sheath Protein Impacts Flagellar Helicity

2000 ◽  
Vol 182 (23) ◽  
pp. 6698-6706 ◽  
Author(s):  
Chunhao Li ◽  
Linda Corum ◽  
David Morgan ◽  
Everett L. Rosey ◽  
Thaddeus B. Stanton ◽  
...  
Keyword(s):  
Blot Analysis ◽  
Type Strain ◽  
Wild Type Strain ◽  
Polyacrylamide Gel Electrophoresis ◽  
Sodium Dodecyl ◽  
Dark Field ◽  
Wild Type ◽  
Brachyspira Hyodysenteriae ◽  
Flagellar Filament ◽  
Cognate Gene

ABSTRACT Spirochete periplasmic flagella (PFs), including those fromBrachyspira (Serpulina),Spirochaeta, Treponema, andLeptospira spp., have a unique structure. In most spirochete species, the periplasmic flagellar filaments consist of a core of at least three proteins (FlaB1, FlaB2, and FlaB3) and a sheath protein (FlaA). Each of these proteins is encoded by a separate gene. Using Brachyspira hyodysenteriae as a model system for analyzing PF function by allelic exchange mutagenesis, we analyzed purified PFs from previously constructedflaA::cat,flaA::kan, andflaB1::kan mutants and newly constructed flaB2::cat andflaB3::cat mutants. We investigated whether any of these mutants had a loss of motility and altered PF structure. As formerly found withflaA::cat,flaA::kan, andflaB1::kan mutants,flaB2::cat andflaB3::cat mutants were still motile, but all were less motile than the wild-type strain, using a swarm-plate assay. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis indicated that each mutation resulted in the specific loss of the cognate gene product in the assembled purified PFs. Consistent with these results, Northern blot analysis indicated that each flagellar filament gene was monocistronic. In contrast to previous results that analyzed PFs attached to disrupted cells, purified PFs from a flaA::cat mutant were significantly thinner (19.6 nm) than those of the wild-type strain and flaB1::kan,flaB2::cat, andflaB3::cat mutants (24 to 25 nm). These results provide supportive genetic evidence that FlaA forms a sheath around the FlaB core. Using high-magnification dark-field microscopy, we also found thatflaA::cat andflaA::kan mutants produced PFs with a smaller helix pitch and helix diameter compared to the wild-type strain and flaB mutants. These results indicate that the interaction of FlaA with the FlaB core impacts periplasmic flagellar helical morphology.

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