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Infection and Immunity, September 2005, p. 6187-6190, Vol. 73, No. 9
0019-9567/05/$08.00+0 doi:10.1128/IAI.73.9.6187-6190.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Department of Biochemistry, Pharmacology, and Toxicology,1 Department of Epizootiology and Veterinary Administration with Clinic,2 Department and Clinic of Obstetrics, Ruminant Diseases, and Animal Health, Faculty of Veterinary Medicine, Agricultural University of Wroclaw, 50-375 Wroclaw, Poland,3 Department of Immunochemistry, Ludwik Hirszfeld Institute of Immunology and Experimental Therapy, Polish Academy of Sciences, 53-114 Wroclaw, Poland4
Received 22 February 2005/ Returned for modification 4 April 2005/ Accepted 6 May 2005
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It has been shown that, in contrast to most Salmonella serovars, S. enterica serovar Gallinarum biovar Gallinarum and S. enterica serovar Gallinarum biovar Pullorum do not express the hemagglutinating, mannose-sensitive type 1 fimbriae; however, they produce morphologically similar filamentous organelles which were named type 2 fimbriae (5, 13). The type 1 fimbriae of the genus Salmonella are composed primarily of FimA protein subunits (9, 12). However, for direct binding to oligomannosidic structures, another protein, called FimH adhesin and located at the distal end of the fimbrial shaft, is responsible (7, 10, 17). An electron microscope study, using antibodies directed against type 1 fimbriae, and Southern blotting with gene probes for type 1 fimbriae confirmed that type 2 fimbriae are, in fact, type 1 fimbriae (3). Recent cloning and sequencing of fimH genes from serovar Typhimurium and biovar Pullorum (6) strongly supported the view that the biovars Gallinarum and Pullorum are able to produce type 1 fimbriae which have lost their functional activity. However, neither the abilities of biovar Gallinarum and biovar Pullorum to produce FimH adhesins nor the consequences of the amino acid substitutions on the adhesive properties of these proteins were ever studied carefully; therefore, the present study was undertaken to address these problems.
The presence of FimH and FimA proteins was shown in type 1 fimbriae of biovar Gallinarum and biovar Pullorum purified by the method of Müller et al. (11). FimH and FimA proteins of biovar Gallinarum and biovar Pullorum type 1 fimbriae were detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting using the obtained anti-FimH rabbit and anti-FimA chicken polyclonal antibodies (Fig. 1). Because of the high homology in the amino acid sequences of FimH (GenBank accession numbers AAN64295, AAA75420, AAR83178, and AAR83177) and FimA (4, 14) among different Salmonella serovars/biovars, heterologous antisera raised against the respective proteins from Salmonella enterica serovar Typhimurium (FimH) and Salmonella enterica serovar Enteritidis (FimA) were used to identify these proteins from both avian-adopted biovars. Antiserum against FimH proteins was obtained by immunization of rabbits with S. enterica serovar Typhimurium recombinant FimH proteins purified on Ni-nitrilotriacetic acid (Ni-NTA) resin (see below), and the immunoglobulin G (IgG) fraction was then purified on protein A Sepharose (Amersham Pharmacia Biotech). Antiserum against FimA proteins was obtained by immunization of hens with recombinant FimA proteins purified on the same Ni-NTA resin (8). In addition, the presence of both fimbrial proteins on the surface of biovar Gallinarum and biovar Pullorum cells was shown by enzyme-linked immunosorbent assay (ELISA) with the same antibodies (data not shown). Bound anti-FimH and anti-FimA antibodies were detected by using alkaline phosphatase-conjugated goat anti-rabbit IgG (Dako) and alkaline phosphatase-conjugated rabbit anti-chicken IgG (Chemicon), respectively.
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FIG. 1. Immunodetection of FimA and FimH proteins of biovar Gallinarum (lanes 1, 3, and 5) and biovar Pullorum (lanes 2, 4, and 6). Type 1 fimbriae (10 µg), purified according to the method of Müller et al. (11), were dissolved in Laemmli sample buffer supplemented with glycine at pH 2.2 and subjected to SDS-PAGE under reducing conditions in 12% gel and electrophoretically transferred to nitrocellulose. The positions of the molecular mass standards (in kDa) are shown on the left. (A) SDS-PAGE gel stained with Coomassie brilliant blue; (B and C) Western blots stained with polyclonal chicken anti-FimA (B) and polyclonal rabbit anti-FimH (C) antibodies.
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cells were transformed with the expression vector pTrcHis2b (Invitrogen) containing cloned fimH genes from biovar Gallinarum (G.fimH/pTrcHis2b), biovar Pullorum (P.fimH/pTrcHis2b), and S. enterica serovar Typhimurium (T.fimH/pTrcHis2b). The fimH genes from biovar Galliarum, biovar Pullorum, and S. enterica serovar Typhimurium were cloned by amplification of the genomic DNA sequences with PCR by use of the primers 5'-fim (5'-CGCGGATCCAATGAAAATATACTCAGC-3') and 3'-fim (5'-GCGTCTAGAGCATCATAATCGACTCG-3') based on the published sequence of S. enterica serovar Typhimurium (GenBank accession no. L19338). The PCR primers contained additional sequences corresponding to a BamHI restriction site in the primer 5'-fim and to XbaI in 3'-fim. The fimH genes were amplified as follows: 25 cycles of denaturation (94°C for 1 min), annealing (54°C for 1 min), and elongation (72°C for 1 min). The resulting PCR products were digested with the respective enzymes and ligated to the corresponding sites of pTrcHis2b plasmid. FimH proteins expressed in E. coli were purified on Ni-NTA affinity resin because of the presence of a six-His tag in the C terminus of their polypeptide chain. Coomassie brilliant blue staining of SDS-PAGE-separated proteins revealed the presence of a major band with an apparent molecular mass of about 36 kDa, corresponding to FimH monomer (Fig. 2A). By use of monoclonal antibody 9E10.2 (no. CRL-1792; American Type Culture Collection) directed against the c-myc epitope, which is a part of the recombinant protein, and secondary alkaline phosphatase-conjugated goat anti-mouse immunoglobulins (Dako), the identities of these proteins as FimH adhesins were confirmed (Fig. 2B).
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FIG. 2. Coomassie brilliant blue-stained SDS-PAGE (A) and immunostaining (B) of recombinant FimH adhesins from biovar Gallinarum (lanes 1), biovar Pullorum (lanes 2), and Salmonella enterica serovar Typhimurium (lanes 3). FimH proteins (10 µg), purified on Ni-NTA resin, were subjected to SDS-PAGE under reducing conditions in 10% gel. The migration positions of protein standards (in kDa) are indicated on the left.
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ski and Roy (2). As expected, both recombinant adhesins did not bind, in contrast to S. enterica serovar Typhimurium FimH, to any of the glycoproteins carrying high-mannose structures, as found by Western blotting (Fig. 3). In addition, by use of cellular ELISA, it was shown that FimH adhesins did not bind to human HT-29 colon carcinoma cells (Fig. 5). To detect FimH proteins, rabbit anti-FimH IgG and alkaline phosphatase-conjugated goat anti-rabbit IgG (Dako) were used.
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FIG. 3. Western blot analysis of FimH binding to glycoproteins carrying high-mannose-type oligosaccharide chains. Binding of the recombinant FimH adhesins from Salmonella enterica serovar Typhimurium (A), biovar Gallinarum (B), and biovar Pullorum (C) to mannan-BSA (lanes 1), HRP (lanes 2), and RNase B (lanes 3). Individual glycoproteins (10 µg) were subjected to SDS-PAGE under reducing conditions in 10% gel and electrophoretically transferred to nitrocellulose. The positions of the molecular mass standards (in kDa) are shown on the left.
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FIG. 5. Binding of serially diluted FimH adhesins (starting from 100 µg/ml) to a monolayer of human colon cancer HT-29 cells growing in 96-well plates. , FimH from S. enterica serovar Typhimurium; , native FimH from biovar Gallinarum; , mutated FimH from biovar Gallinarum; , native FimH from biovar Pullorum; , mutated FimH from biovar Pullorum.
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as described for wild-type FimH adhesins. The construction of FimH proteins in which isoleucine was replaced by threonine fully confirmed our hypothesis. Both mutants bound well to glycoproteins carrying high-mannose oligosaccharides (Fig. 4) as well as colon carcinoma cells (Fig. 5) as shown by Western blotting and ELISA with rabbit polyclonal antibodies directed against FimH and alkaline phosphatase-conjugated goat anti-rabbit IgG. Because the only common difference in amino acid sequence between active and inactive FimH adhesins is the presence of isoleucine instead of threonine at position 78, our data strongly suggest that just one amino acid difference is fully responsible for the loss of adhesive properties by type 1 fimbriae from biovar Gallinarum and biovar Pullorum. At this point, it is difficult to hypothesize what the biological consequences of such a mutation are, e.g., the effect on the host specificities of these avian-adopted biovars. Recently, it was shown that biovar Gallinarum and biovar Pullorum expressing S. enterica serovar Typhimurium strain LT2 type 1 fimbriae adhered 10 to 20 times better to human epithelial HEp-2 cells and were characterized by 20- to 60-fold-increased invasiveness (18). In addition, a 32% increase in the number of M-cell ruffles was observed in a murine-ligated ileal loop model.
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FIG. 4. Western blot analysis of mutant FimH adhesins binding to glycoproteins carrying high-mannose-type oligosaccharide chains. Binding of the mutant FimH proteins from biovars Gallinarum and Pullorum in the absence (A and C) and presence (B and D) of 0.2 M D-mannose to mannan-BSA (lanes 1), HRP (lanes 2), and RNase B (lanes 3). The mutants, constructed by site-directed mutagenesis, are identical to wild-type adhesins except at the position corresponding to the amino acid at position 78, where isoleucine was replaced by threonine (I78T). Individual glycoproteins (10 µg) were subjected to SDS-PAGE under reducing conditions in 10% gel and electrophoretically transferred to nitrocellulose. The positions of the molecular mass standards (in kDa) are shown on the left.
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Nucleotide sequence accession numbers. The sequences for the FimH protein reported in this study have been submitted to GenBank under accession numbers AAR83178, AAR83177, and AAN64295.
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ski, J., and R. Roy. 1998. High temperature conjugation of proteins with carbohydrates. Glycoconj. J. 15:131-138.[CrossRef][Medline]
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