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Kreida S, Narita A, Johnson MD, Tocheva EI, Das A, Ghosal D, Jensen GJ. Cryo-EM structure of the Agrobacterium tumefaciens T4SS-associated T-pilus reveals stoichiometric protein-phospholipid assembly. Structure 2023; 31:385-394.e4. [PMID: 36870333 PMCID: PMC10168017 DOI: 10.1016/j.str.2023.02.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2022] [Revised: 01/08/2023] [Accepted: 02/07/2023] [Indexed: 03/06/2023]
Abstract
Agrobacterium tumefaciens causes crown gall disease in plants by the horizontal transfer of oncogenic DNA. The conjugation is mediated by the VirB/D4 type 4 secretion system (T4SS) that assembles an extracellular filament, the T-pilus, and is involved in mating pair formation between A. tumefaciens and the recipient plant cell. Here, we present a 3 Å cryoelectron microscopy (cryo-EM) structure of the T-pilus solved by helical reconstruction. Our structure reveals that the T-pilus is a stoichiometric assembly of the VirB2 major pilin and phosphatidylglycerol (PG) phospholipid with 5-start helical symmetry. We show that PG head groups and the positively charged Arg 91 residues of VirB2 protomers form extensive electrostatic interactions in the lumen of the T-pilus. Mutagenesis of Arg 91 abolished pilus formation. While our T-pilus structure is architecturally similar to previously published conjugative pili structures, the T-pilus lumen is narrower and positively charged, raising questions of whether the T-pilus is a conduit for ssDNA transfer.
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Affiliation(s)
- Stefan Kreida
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA; Department of Microbiology, Tumor and Cell Biology, Karolinska Institute, 171 77 Stockholm, Sweden
| | - Akihiro Narita
- Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
| | - Matthew D Johnson
- Department of Biochemistry and Pharmacology, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, VIC, Australia
| | - Elitza I Tocheva
- Department of Microbiology and Immunology, Life Sciences Institute, The University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, Canada
| | - Anath Das
- Department of Biochemistry, Molecular Biology and Biophysics, and Microbial and Plant Genomics Institute, University of Minnesota, Minneapolis, MN 55455, USA
| | - Debnath Ghosal
- Department of Biochemistry and Pharmacology, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, VIC, Australia; ARC Centre for Cryo-electron Microscopy of Membrane Proteins, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, VIC, Australia.
| | - Grant J Jensen
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA; Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84604, USA.
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Lévesque C, Vadeboncoeur C, Chandad F, Frenette M. Streptococcus salivarius fimbriae are composed of a glycoprotein containing a repeated motif assembled into a filamentous nondissociable structure. J Bacteriol 2001; 183:2724-32. [PMID: 11292790 PMCID: PMC99487 DOI: 10.1128/jb.183.9.2724-2732.2001] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Streptococcus salivarius, a gram-positive bacterium found in the human oral cavity, expresses flexible peritrichous fimbriae. In this paper, we report purification and partial characterization of S. salivarius fimbriae. Fimbriae were extracted by shearing the cell surface of hyperfimbriated mutant A37 (a spontaneous mutant of S. salivarius ATCC 25975) with glass beads. Preliminary experiments showed that S. salivarius fimbriae did not dissociate when they were incubated at 100 degrees C in the presence of sodium dodecyl sulfate. This characteristic was used to separate them from other cell surface components by successive gel filtration chromatography procedures. Fimbriae with molecular masses ranging from 20 x 10(6) to 40 x 10(6) Da were purified. Examination of purified fimbriae by electron microscopy revealed the presence of filamentous structures up to 1 microm long and 3 to 4 nm in diameter. Biochemical studies of purified fimbriae and an amino acid sequence analysis of a fimbrial internal peptide revealed that S. salivarius fimbriae were composed of a glycoprotein assembled into a filamentous structure resistant to dissociation. The internal amino acid sequence was composed of a repeated motif of two amino acids alternating with two modified residues: A/X/T-E-Q-M/phi, where X represents a modified amino acid residue and phi represents a blank cycle. Immunolocalization experiments also revealed that the fimbriae were associated with a wheat germ agglutinin-reactive carbohydrate. Immunolabeling experiments with antifimbria polyclonal antibodies showed that antigenically related fimbria-like structures were expressed in two other human oral streptococcal species, Streptococcus mitis and Streptococcus constellatus.
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Affiliation(s)
- C Lévesque
- Groupe de Recherche en Ecologie Buccale, Faculté de Médecine Dentaire, Université Laval, Quebec City, Quebec, Canada
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Frost LS, Ippen-Ihler K, Skurray RA. Analysis of the sequence and gene products of the transfer region of the F sex factor. Microbiol Rev 1994; 58:162-210. [PMID: 7915817 PMCID: PMC372961 DOI: 10.1128/mr.58.2.162-210.1994] [Citation(s) in RCA: 274] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Bacterial conjugation results in the transfer of DNA of either plasmid or chromosomal origin between microorganisms. Transfer begins at a defined point in the DNA sequence, usually called the origin of transfer (oriT). The capacity of conjugative DNA transfer is a property of self-transmissible plasmids and conjugative transposons, which will mobilize other plasmids and DNA sequences that include a compatible oriT locus. This review will concentrate on the genes required for bacterial conjugation that are encoded within the transfer region (or regions) of conjugative plasmids. One of the best-defined conjugation systems is that of the F plasmid, which has been the paradigm for conjugation systems since it was discovered nearly 50 years ago. The F transfer region (over 33 kb) contains about 40 genes, arranged contiguously. These are involved in the synthesis of pili, extracellular filaments which establish contact between donor and recipient cells; mating-pair stabilization; prevention of mating between similar donor cells in a process termed surface exclusions; DNA nicking and transfer during conjugation; and the regulation of expression of these functions. This review is a compendium of the products and other features found in the F transfer region as well as a discussion of their role in conjugation. While the genetics of F transfer have been described extensively, the mechanism of conjugation has proved elusive, in large part because of the low levels of expression of the pilus and the numerous envelope components essential for F plasmid transfer. The advent of molecular genetic techniques has, however, resulted in considerable recent progress. This summary of the known properties of the F transfer region is provided in the hope that it will form a useful basis for future comparison with other conjugation systems.
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Affiliation(s)
- L S Frost
- Department of Microbiology, University of Alberta, Edmonton, Canada
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Affiliation(s)
- W Paranchych
- Department of Biochemistry, University of Alberta, Edmonton, Canada
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Finlay BB, Frost LS, Paranchych W. Nucleotide sequence of the tra YALE region from IncFV plasmid pED208. J Bacteriol 1986; 168:990-8. [PMID: 2877970 PMCID: PMC213581 DOI: 10.1128/jb.168.2.990-998.1986] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The pED208 plasmid is a 90-kilobase conjugative plasmid which is the derepressed form of Fo lac plasmid (IncFV). A 3.3-kilobase HindIII-PstI fragment from the pED208 plasmid was cloned and sequenced and was found to contain four open reading frames which were highly homologous to the traA, traL, traE, and traY gene products of the F plasmid. The pED208 traA propilin protein was 119 amino acids in length, consisting of a leader sequence of 55 amino acids and a mature pilin subunit of 64 residues. The leader sequence contained a hydrophobic region followed by a classic signal peptidase cleavage site (Ala-Ser-Ala-55). F and pED208 pilin proteins shared 27 conserved residues and had similar predicted secondary structures. The pED208 traA and traL genes were separated by a single base pair, and no ribosome binding site preceded the traL gene. The pED208 traY gene contained an IS2 insertion element in orientation II 180 nucleotides (60 residues) upstream of the traY stop codon. This insertion of IS2 resulted in a predicted fusion peptide of 69 residues for traY which may provide the observed traY activity. Since IS2 is absent in the wild-type plasmid, Fo lac, derepression and concomitant multipiliation may be due to the insertion of IS2 providing constitutive expression of the pED208 tra operon.
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Worobec EA, Frost LS, Pieroni P, Armstrong GD, Hodges RS, Parker JM, Finlay BB, Paranchych W. Location of the antigenic determinants of conjugative F-like pili. J Bacteriol 1986; 167:660-5. [PMID: 2426247 PMCID: PMC212940 DOI: 10.1128/jb.167.2.660-665.1986] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The amino terminus of the pilin protein constitutes the major epitope of F-like conjugative pili studied to date (F, ColB2, R1-19, R100-1, and pED208). Anti-pED208 pilus antibodies were passed through a CNBr-Sepharose affinity column linked to bovine serum albumin which was conjugated to a synthetic peptide, AcP(1-12), containing the major epitope at the amino terminus of pED208 pilin. This allowed the separation of two classes of antibodies; one was specific for the amino terminus and bound to the column, while the other, which recognizes a second epitope on the pilus, did not bind to the column. In addition, antibodies were raised against two amino-terminal peptide-bovine serum albumin conjugates [AcP(1-8) and AcP(1-12)] to ensure a source of pure, high-titer antibodies directed against the amino terminus. The location of these antibodies on intact pili was assayed by immunoelectron microscopy with a protein A-gold technique. The amino terminus-specific antibodies did not bind to the sides of the pili but appeared to be associated with the pilus tip. In addition, these antibodies were found to bind to the vesicle-like structure at the base of the pilus. The anti-pilus antibodies not specific for the amino terminus (unbound immunoglobulin G) were found to bind to the sides of the pilus. Anti-F and anti-ColB2 pilus antibodies bound to the sides of F, ColB2, and R1-19 pili, which have only their secondary epitope in common. The carboxyl-terminal lysine of R1-19 pilin prevents the absorption of anti-F plus antiserum but not anti-ColB2 pilus antiserum to the sides of the pilus, presumably by interfering with the recognition of this secondary epitope.
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Finlay BB, Paranchych W. Nucleotide sequence of the surface exclusion genes traS and traT from the IncF0 lac plasmid pED208. J Bacteriol 1986; 166:713-21. [PMID: 3011738 PMCID: PMC215180 DOI: 10.1128/jb.166.3.713-721.1986] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
pED208 is a 90-kilobase conjugative plasmid belonging to the incompatibility group IncF0 lac. The surface exclusion system from this plasmid was cloned and sequenced, and two genes demonstrated exclusion ability. traS encoded a 186-amino-acid hydrophobic protein which, when transcribed from a vector promoter, caused exclusion of pED208. The product of traT (TraTp) was a 245-residue protein which was highly expressed independently of a vector promoter in Escherichia coli minicells. The TraTp from pED208 was homologous with traT products from the IncF plasmids R-100 and F (80% homology), but recombinants containing the pED208 surface exclusion system excluded F poorly.
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Frost LS, Finlay BB, Opgenorth A, Paranchych W, Lee JS. Characterization and sequence analysis of pilin from F-like plasmids. J Bacteriol 1985; 164:1238-47. [PMID: 2999074 PMCID: PMC219321 DOI: 10.1128/jb.164.3.1238-1247.1985] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Conjugative pili are expressed by derepressed plasmids and initiate cell-to-cell contact during bacterial conjugation. They are also the site of attachment for pilus-specific phages (f1, f2, and QB). In this study, the number of pili per cell and their ability to retract in the presence of cyanide was estimated for 13 derepressed plasmids. Selected pilus types were further characterized for reactivity with anti-F and anti-ColB2 pilus antisera as well as two F pilus-specific monoclonal antibodies, one of which is specific for a sequence common to most F-like pilin types (JEL92) and one which is specific for the amino terminus of F pilin (JEL93). The pilin genes from eight of these plasmids were cloned and sequenced, and the results were compared with information on F, ColB2, and pED208 pilin. Six pilus groups were defined: I, was F-like [F, pED202(R386), ColV2-K94, and ColVBtrp]; IIA was ColB2-like in sequence but had a lowered sensitivity to f1 phage due to its decreased ability for pilus retraction [pED236(ColB2) and pED203(ColB4)]; IIB was ColB2-like but retained f1 sensitivity [pED200(R124) and pED207(R538-1)]; III contained R1-19, which had a ColB2-like amino terminus but had an additional lysine residue at its carboxy terminus which may affect its phage sensitivity pattern and its antigenicity; IV was R100-1-like [R100-1 and presumably pED241(R136) and pED204(R6)] which had a unique amino-terminal sequence combined with a carboxy terminus similar to that of F. pED208(Folac) formed group V, which was multipiliated and exhibited poor pilus retraction although it retained full sensitivity to f1 phage. The pED208 pilin gene could not be cloned at this time since it shared no homology with the pilin gene of the F plasmid.
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Abstract
F-like conjugative pili are expressed by plasmids with closely related transfer systems. They are tubular filaments that are composed of repeating pilin subunits arranged in a helical array. Both F and ColB2 pilin have nearly identical protein sequences, and both contain an acetylated amino-terminal alanine residue. However, they differ by a few amino acid residues at their amino termini. Rabbit antisera raised against purified F and ColB2 pili are immunologically cross-reactive by only 25%, as measured by a competition enzyme-linked immunosorbent assay (ELISA). A tryptic peptide corresponding to the first 15 amino acid residues of ColB2 pilin was isolated and found to remove nearly 80% of ColB2 pilus-directed rabbit antibodies. The corresponding tryptic peptide from F pilin, which reacted with anti-F pilus antibodies to remove 80%, was less than 20% reactive with anti-ColB2 pilus antiserum. Cleavage of these peptides with cyanogen bromide (at a methionine residue approximately in the middle of the peptide) did not affect the antigenicity of these peptides. Synthetic N alpha-acetylated peptides corresponding to the first eight amino acids of F pilin (Ac-Ala-Gly-Ser-Ser-Gly-Gln-Asp-Leu-COOH) and the first six amino acids of ColB2 pilin (Ac-Ala-Gln-Gly-Gln-Asp-Leu-COOH) were prepared and tested by competition ELISA with homologous and heterologous anti-pilus antisera. The F peptide F(1-8) inhibited the interaction of F pili and anti-F pilus antiserum to 80%, while the ColB2 peptide ColB2(1-6) inhibited anti-ColB2 pilus antiserum reacting with ColB2 pili by greater than 60%. The two peptides F(1-8) and ColB2(1-6) were inactive by competition ELISAs with heterologous antisera. These results suggest that the major antigenic determinant of both F and ColB2 pili is at the amino terminus of the pilin subunit and that 80% of antibodies raised against these pili are specific for this region of the pilin molecule.
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Worobec EA, Paranchych W, Parker JM, Taneja AK, Hodges RS. Antigen-antibody interaction. The immunodominant region of EDP208 pili. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(20)71190-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Finlay BB, Frost LS, Paranchych W. Localization, cloning, and sequence determination of the conjugative plasmid ColB2 pilin gene. J Bacteriol 1984; 160:402-7. [PMID: 6090427 PMCID: PMC214732 DOI: 10.1128/jb.160.1.402-407.1984] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
ColB2 is a colicin-producing, 96-kilobase plasmid which encodes a conjugative system that is similar, but not identical, to F. A restriction map of this plasmid was generated, and DNA homology studies between F and ColB2 plasmids revealed homology only between their transfer operons. The locations of the ColB2 transfer operon and ColB2 pilin gene were localized on this restriction map. The gene encoding ColB2 pilin, traA, was cloned and sequenced. The pilin protein of ColB2 is identical to F, except at the amino terminus, where ala-gln of ColB2 pilin corresponds to Ala-Gly-Ser-Ser of F pilin. This is due to a 6-base-pair deletion in the ColB2 pilin gene. Biochemical studies on tryptic peptides derived from ColB2 pilin demonstrate the location of this gene to be correct. There is a putative signal peptidase cleavage site after the sequence Ala-Met-Ala, giving a signal peptide of 51 amino acids and a mature pilin protein of 68 amino acids (7,000 daltons). The amino terminus is blocked, probably with an acetyl group. A chimera containing the ColB2 pilin gene was able to complement an F traA mutant, demonstrating that the pilus assembly proteins of F can utilize the ColB2 pilin protein to form a pilus.
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Frost LS, Paranchych W, Willetts NS. DNA sequence of the F traALE region that includes the gene for F pilin. J Bacteriol 1984; 160:395-401. [PMID: 6090426 PMCID: PMC214731 DOI: 10.1128/jb.160.1.395-401.1984] [Citation(s) in RCA: 74] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The complete sequence of a 1.4-kilobase PstI fragment containing the F transfer genes traA, -L, and -E is presented. The traA reading frame has been located both genetically and by comparing the primary structure of F pilin (the traA product) predicted by the DNA sequence to the amino acid composition and sequence of N- and C-terminal peptides isolated from purified F pilin. Taken together, these data show that there is a leader peptide of 51 amino acids and that F pilin contains 70 amino acids, giving molecular weights of 13,200 for F propilin and 7,200 for mature F pilin. Secondary structure predictions for F pilin revealed a reverse turn that precedes the sequence Ala-Met-Ala51, a classic signal peptidase cleavage site. The N-terminal alanine residue is blocked by an acetyl group as determined by 1H-nuclear magnetic resonance spectroscopy. The traL and traE genes encode proteins of molecular weights 10,350 and 21,200, respectively. According to DNA sequence predictions, these proteins do not contain signal peptide leader sequences. Secondary structure predictions for these proteins are in accord with traLp and traEp being membrane proteins in which hydrophobic regions capable of spanning the membrane are linked by sequences that form turns and carry positively charged residues capable of interacting with the membrane surface.
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Worobec EA, Taneja AK, Hodges RS, Paranchych W. Localization of the major antigenic determinant of EDP208 pili at the N-terminus of the pilus protein. J Bacteriol 1983; 153:955-61. [PMID: 6185467 PMCID: PMC221719 DOI: 10.1128/jb.153.2.955-961.1983] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Trypsin digestion of pilin monomers from EDP208 conjugative pili causes cleavage of Lys12 to yield an N-terminal dodecapeptide, ET1 (Mr approximately equal to 1,500), and the remaining C-terminal fragment, ER (Mr approximately equal to 10,000). Using the amino acid sequence for ET1 provided by Frost et al. (J. Bacteriol. 153:950-954), we synthesized the N-terminal dodecapeptide chemically, conjugated it to bovine serum albumin, and subjected it to immunological studies. Antisera prepared against intact EDP208 pili as well as against the synthetic ET1-BSA conjugate were used in experiments involving an enzyme-linked immunosorbant assay and electrophoretic transfer of proteins from sodium dodecyl sulfate-polyacrylamide gels to nitrocellulose sheets. Both experimental approaches showed strong reactivity between the synthetic dodecapeptide and antiserum raised against whole pili. It was also found that antiserum raised against the synthetic peptide was reactive against intact pilus protein, indicating that the N-terminal dodecapeptide is an important antigenic determinant of the EDP208 pilus protein. Additional studies showed that the C-terminal fragment, ER, may contain one or two additional antigenic sites.
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