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Infection and Immunity, July 2002, p. 3427-3432, Vol. 70, No. 7
0019-9567/02/$04.00+0 DOI: 10.1128/IAI.70.7.3427-3432.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Department of Bacterial Toxinology, Research Institute for Microbial Diseases, Osaka University, Yamada-oka 3-1, Suita, Osaka 565-0871, Japan
Received 25 January 2002/ Returned for modification 18 March 2002/ Accepted 1 April 2002
| ABSTRACT |
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| INTRODUCTION |
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DNT is a single-chain polypeptide which consists of 1,464 amino acids with a calculated molecular mass of 160,602 (13). Previously, we localized the catalytic domain of DNT to the C-terminal region from Ile1176 to the C-terminal end. We also found that the N-terminal fragment spanning Met1 to Pro531 of DNT competitively blocked the intoxication of cells by the full-length DNT (13), implying that this fragment retains the receptor-binding or internalizing property. In the present study, we attempted to define the N-terminal receptor-binding region of DNT by using a series of toxin mutants with various lengths and a monoclonal antibody (MAb) that neutralizes the toxin. The results presented here indicate that DNT binds to the cells through the N-terminal region consisting of 54 amino acids, in which the MAb recognized the region including Arg44.
| MATERIALS AND METHODS |
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-minimum essential medium (
-MEM; Gibco Laboratories, Grand Island, N.Y.) supplemented with 10% fetal calf serum under 5% CO2 in air. The cells were subcultured every 3 days at a dilution of 1:10. Anti-DNT MAbs were prepared as described previously (15) with a slight modification. X63-Ag8-6.5.3 myeloma cells were used for the production of the anti-DNT MAbs.
Neutralization assay.
MC3T3-E1 cells were plated in wells of 24-well plates or in 35-mm culture dishes at an initial density of 1,300 cells per cm2. The cells were grown for 24 h, washed three times with serum-free
-MEM, and incubated in the same medium for an additional 24 h. DNT was added to the culture at given concentrations after preincubation with or without MAb in serum-free
-MEM at 37°C for 30 min. After incubation for 12 h, the cells were examined for the formation of actin stress fibers and the modification of intracellular Rho by a method reported previously (10). The DNT-induced polynucleation of the cells was assessed as described elsewhere (13).
Construction of expression vectors for DNT mutants. The expression vectors for DNT and its mutants were constructed as follows. pBSDNT, pUCDNT3', pUCSTOP, pETDNTwt, pBSSTOP, pGEXDNT1-531, pETDNT1-531-glutathione S-transferase (GST), and pGEXGST-DNT523-1464 were constructed as previously described (13).
(i) Series of 3'-end truncation and internal deletion mutants of DNT. The EcoRI-ApaLI (blunted), EcoRI-EcoRV, or EcoRI-HincII fragment of pUCDNT3' was inserted into the SmaI-EcoRI site of pUCSTOP. The fragments obtained by treatment of these plasmids with EcoRI and HindIII were separately introduced into the EcoRI-HindIII site of pETDNTwt. The resultant plasmids were designated psApaLI encoding DNT Met1-Cys1305, psRV encoding DNT Met1-Asp1101, and psHinc encoding DNT Met1-Val889. Expression vectors for mutants of DNT with internal deletions, dRV (EcoRV), dSP (SmaI-PvuII), dSph (SphI), dEM (EcoRI-MfeI), and dSX (SalI-XhoI) were constructed by treatment of pETDNTwt with the restriction enzymes shown in parentheses and recircularization.
(ii) pBSGST. The GST gene was amplified by PCR with the primers 5'-AATATGCGGCCGCTCATGTCCCCTATACTAGG-3' (the underline indicates an NotI site) and 5'-GGCAGATCGTCAGTCAGTCACG-3', with pGEX4T3 (Amersham Pharmacia Biotech) as a template. The amplified DNA was digested with NotI and EcoRI and inserted into the NotI-EcoRI site of pBSSTOP. The resultant plasmid was designated pBSGST and used for the preparation of DNT mutant genes with C terminally-tagged GST.
(iii) pETDNT1-344-GST. pETDNTwt was digested with StuI, ligated with a phosphorylated 10-mer NotI linker, and digested with NcoI and NotI. The resultant DNA fragment encoding DNT from Met1-Glu344 and the NotI-HindIII fragment of pBSGST were ligated with pET21d (Novagen, Inc., Madison, Wis.) treated with NcoI and HindIII.
(iv) pETDNT1-244-GST. The NotI site of pBSGST was replaced with an NdeI site by treatment with NotI and T4 DNA polymerase and ligation with a phosphorylated 12-mer NdeI linker. The GST gene was excised by treatment with NdeI and HindIII and inserted into the NdeI-HindIII site of pETDNT1-531-GST.
(v) pETDNT1-94-GST. pETDNT1-244-GST was digested with XhoI, and an NdeI site was added by ligation with a 10-mer NdeI linker. A DNA fragment encoding DNT Met1-Leu94 was excised from the plasmid by digestion with NcoI and NdeI and inserted into the NcoI-NdeI site of pETDNT1-244-GST.
(vi) pETDNT1-54-GST. A DNA fragment encoding DNT Met1-Glu54 was amplified by PCR with the primers 5'-GGGCCATGGATAAAGATGAATCGGCATTGC-3', where the underline indicates an NcoI site, and 5'-GGCATATGTTTCGCCAAACAGCGCGAATTCGGCCTTC-3', where the underline indicates an NdeI site and with pETDNTwt as a template. The DNA fragment was digested with NcoI and NdeI and inserted into the NcoI-NdeI site of pETDNT1-243-GST.
(vii) pETDNT47-244-GST. The EcoRI site of pETDNTwt was replaced with NcoI by digestion with EcoRI and ligation with a 12-mer NcoI linker. A DNA fragment encoding DNT Ala47-Gly244 was excised by digestion with NcoI and NdeI and ligated with pETDNT1-244-GST digested with the same enzymes.
(viii) pGEXDNT1-54-hexahistidine (His6). A gene was amplified by PCR with the primers 5'-GGATCCGATAAAGATGAATCGGCATTGC-3', where the underline indicates a BamHI site, and 5'-CCGAGCTCTCGCCAAACAGCGCGAATTCGG-3', where the underline indicates an SacI site, and pETDNTwt as a template DNA. The amplified DNA was digested with BamHI and SacI and ligated with pGST-CAN4 (14) treated with the same enzymes.
(viii) pQEDNTwt. The BamHI-NdeI fragment of pGEXDNT1-531 was ligated with the NdeI-HindIII fragment of pETDNTwt and pQE40 (Qiagen) digested with BamHI and HindIII.
(ix) pQEDNT(R44G), pQEDNT(R44S), and pQEDNT(R44K). pQEDNT(R44G), pQEDNT(R44S), and pQEDNT(R44K) were prepared from pQEDNTwt by site-directed mutagenesis with a QuickChange kit (Stratagene, La Jolla, Calif.).
Expression and purification of recombinant proteins. The expression vectors for DNT mutants were introduced into Escherichia coli BL21(DE3). The bacteria were cultivated in Luria-Bertani broth containing 50 µg of ampicillin/ml and induced to produce the proteins by using 1 mM IPTG (isopropyl-ß-D-thiogalactopyranoside). The GST fusion proteins were purified with glutathione-Sepharose 4B (Amersham Pharmacia Biotech). The His6-tagged proteins were purified with His-Bind Resin (Novagen).
Microinjection of anti-DNT antibodies. MC3T3-E1 cells were seeded at an initial density of 520 cells per cm2 on coverslips. The cells were grown for 24 h, washed three times with serum-free Dulbecco modified Eagle medium (Gibco Laboratories), and incubated in the same medium for 48 h at 37°C. The cells were injected with 50 µg of anti-DNT polyclonal antibody or 1 mg of anti-DNT MAb 2B3/ml. Rabbit immunoglobulin G (IgG; ICN Pharmaceuticals, Inc., Aurora, Ohio) was also microinjected, together with the samples, as an indicator for the injected cells. Microinjection was performed with an Eppendorf micromanipulator (Eppendorf, Humburg, Germany). The cells were incubated for 1 h at 37°C, washed three times with prewarmed Dulbecco modified Eagle medium, and further incubated for 2 h. After the incubation, 5 ng of DNT/ml was added to the culture and incubated for 20 h. The cells were fixed with 3% paraformaldehyde in phosphate-buffered saline (PBS) for 10 min, washed three times with PBS, and permeabilized with 0.5% Triton X-100 in PBS for 5 min at room temperature. The cells were then incubated with 2.5 U of Alexa 586-phalloidin (Molecular Probes, Inc., Eugene, Oreg.)/ml and 4 µg of Alexa 488-goat anti-rabbit IgG (Molecular Probes)/ml at room temperature for 1 h. The cells were washed three times with PBS and mounted in PermaFlour aqueous mounting medium (Shandon/Lipshaw Co., Pittsburgh, Pa.).
Binding assay. DNT1-54 was iodinated with Na125I by the chloramine-T method. The specific activity of 125I-DNT1-54 was 0.42 to 0.72 mCi/mg of protein. MC3T3-E1 cells suspended in PBS were incubated with 125I-DNT1-54. The 125I-DNT1-54 bound to the cells was separated by filtration through a Millititer-GV plate (Millipore). The filters were washed five times with 200 µl of chilled PBS. The radioactivity retained on the filter was determined by using a gamma counter. The specific binding amount was evaluated from the difference between the means of the radioactive counts in the absence and presence of a 100-fold excess of unlabeled DNT1-54.
Other methods. Protein concentrations were determined by the method of Lowry et al. (16) or Bradford (1). Rabbit anti-DNT serum was obtained as reported previously (8). Anti-DNT IgG or anti-DNT MAbs were purified with an Affi-Gel Protein A MAPS II kit (Bio-Rad, Richmond, Calif.). Expression of the DNT mutants was confirmed by Western blot analysis with the anti-DNT IgG. In the analysis, immunoreactive products were detected with a substrate mixture of 5-bromo-4-chloro-3-indolylphosphate and nitroblue tetrazolium (Promega, Madison, Wis.) or an enhanced chemiluminescence system (Amersham Pharmacia Biotech). The [32P]ADP-ribosylation of Rho was achieved with C3 exoenzyme as described previously (10) and detected by autoradiography with a Fuji BAS 1500 image analyzer (Fuji Film Co., Tokyo, Japan).
| RESULTS |
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| DISCUSSION |
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To localize the functional domains of DNT, we first prepared 10 different MAbs against the toxin. Western blot analysis revealed that all of the MAbs recognized the N-terminal 600-amino-acid region of the toxin (data not shown), implying that the N-terminal region covers the surface of the toxin molecule and therefore presents epitopes. It is conceivable that the N-terminal region on the molecular surface is involved in the binding to the cell receptor. The neutralizing MAb, 2B3, was found to recognize the molecule in the vicinity of Arg44. This region seems to form a loop structure because it was also susceptible to cleavage by trypsin or furin. The results presented here indicate that 2B3 inhibits the binding of DNT to target cells by binding to this putative loop region. The DNT mutants in which Arg44 was substituted with different amino acids so that they would become resistant to furin were inactive on cells (Matsuzawa et al., unpublished). This implies that the loop structure of DNT1-54 plays an important role in the DNT action in addition to the binding to the receptor.
DNT1-54 seems to precisely recognize an unknown cell surface receptor since it strictly bound to the toxin-sensitive cells and not to resistant cells. Direct binding assays with the full-length DNT had long been unsuccessful because nonspecific binding occurred irrespective of cell type (unpublished data). This had constituted an obstacle to elucidating the nature of the binding of DNT to cells. However, we could reduce the nonspecific binding by using DNT1-54 or DNT1-94 as a probe and succeeded in detecting the specific binding, which may provide a way to identify the cell surface receptor. The receptor for DNT is probably an uncommon substance because only a few lines of cells have turned out to be sensitive to DNT. Identification of the DNT receptor is an important issue. In addition, it might be of interest to examine how a binding domain as short as 54 amino acids recognizes the receptor.
| ACKNOWLEDGMENTS |
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This work was supported in part by Grant-in Aid for Scientific Research 11670264 from the Japan Society for the Promotion of Science.
| FOOTNOTES |
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| REFERENCES |
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| 1. | Bradford, M. M. 1976. A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal. Biochem. 72:248-254.[CrossRef][Medline] |
| 2. | Bruckner, I. E., and D. G. Evans. 1939. The toxin of B. parapertussis and the relationship of this organism to H. pertussis and B. bronchiseptica. J. Pathol. Bacteriol. 48:67-78.[CrossRef] |
| 3. | Evans, D. G. 1940. The production of pertussis antitoxin in rabbits and the neutralization of pertussis, parapertussis, and bronchiseptica toxins. J. Pathol. Bacteriol. 51:49-58.[CrossRef] |
| 4. | Hanada, M., K. Shimoda, S. Tomita, Y. Nakase, and Y. Nishiyama. 1979. Production of lesions similar to naturally occurring swine atrophic rhinitis by cell-free sonicated extract of Bordetella bronchiseptica. Jpn. J. Vet. Sci. 41:1-8. |
| 5. | Horiguchi, Y., N. Inoue, M. Masuda, T. Kashimoto, J. Katahira, N. Sugimoto, and M. Matsuda. 1997. Bordetella bronchiseptica dermonecrotizing toxin induces reorganization of actin stress fibers through deamidation of Gln-63 of the GTP-binding protein Rho. Proc. Natl. Acad. Sci. USA 94:11623-11626. |
| 6. | Horiguchi, Y., T. Nakai, and K. Kume. 1991. Effects of Bordetella bronchiseptica dermonecrotic toxin on the structure and function of osteoblastic clone MC3T3-E1 cells Infect. Immun. 59:1112-1116. |
| 7. | Horiguchi, Y., T. Nakai, and K. Kume. 1989. Purification and characterization of Bordetella bronchiseptica dermonecrotic toxin. Microb. Pathog. 6:361-368.[CrossRef][Medline] |
| 8. | Horiguchi, Y., T. Nakai, and K. Kume. 1990. Simplified procedure for purification of Bordetella bronchiseptica dermonecrotic toxin. FEMS Microbiol. Lett. 66:39-43. |
| 9. | Horiguchi, Y., T. Okada, N. Sugimoto, Y. Morikawa, J. Katahira, and M. Matsuda. 1995. Effects of Bordetella bronchiseptica dermonecrotizing toxin on bone formation in calvaria of neonatal rats. FEMS Immunol. Med. Microbiol. 12:29-32.[CrossRef][Medline] |
| 10. | Horiguchi, Y., T. Senda, N. Sugimoto, J. Katahira, and M. Matsuda. 1995. Bordetella bronchiseptica dermonecrotizing toxin stimulates assembly of actin stress fibers and focal adhesions by modifying the small GTP-binding protein rho. J. Cell Sci. 108:3243-3251.[Abstract] |
| 11. | Horiguchi, Y., N. Sugimoto, and M. Matsuda. 1993. Stimulation of DNA synthesis in osteoblast-like MC3T3-E1 cells by Bordetella bronchiseptica dermonecrotic toxin. Infect. Immun. 61:3611-3615. |
| 12. | Iida, T., and T. Okonogi. 1971. Lienotoxicity of Bordetella pertussis in mice. J. Med. Microbiol. 4:51-60.[Medline] |
| 13. | Kashimoto, T., J. Katahira, W. R. Cornejo, M. Masuda, A. Fukuoh, T. Matsuzawa, T. Ohnishi, and Y. Horiguchi. 1999. Identification of functional domains of Bordetella dermonecrotizing toxin. Infect. Immun. 67:3727-3732. |
| 14. | Katahira, J., K. Strasser, A. Podtelejnikov, M. Mann, J. U. Jung, and E. Hurt. 1999. The Mex67p-mediated nuclear mRNA export pathway is conserved from yeast to human. EMBO J. 18:2593-2609.[CrossRef][Medline] |
| 15. | Kohler, G., and C. Milstein. 1975. Continuous cultures of fused cells secreting antibody of predefined specificity. Nature 256:495.[CrossRef][Medline] |
| 16. | Lowry, O. H., N. J. Rosebrough, A. L. Farr, and R. J. Randall. 1951. Protein measurement with the Folin phenol reagent. J. Biol. Chem. 193:265-275. |
| 17. | Masuda, M., L. Betancourt, T. Matsuzawa, T. Kashimoto, T. Takao, Y. Shimonishi, and Y. Horiguchi. 2000. Activation of Rho through a cross-link with polyamines catalyzed by Bordetella dermonecrotizing toxin. EMBO J. 19:521-530.[CrossRef][Medline] |
| 18. | Masuda, M., M. Minami, H. Shime, T. Matsuzawa, and Y. Horiguchi. 2002. In vivo modification of small GTPase Rac and Cdc42 by Bordetella dermonecrotic toxin. Infect. Immun. 70:998-1001. |
| 19. | Wardlaw, A. C., and R. Parton. 1983. Bordetella pertussis toxins, p. 327-371. In F. Dorner and J. Drews (ed.), Phamacology of bacterial toxins. Pergamon Press, Ltd., Oxford, England. |
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