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Infection and Immunity, December 2002, p. 7153-7155, Vol. 70, No. 12
0019-9567/02/$04.00+0     DOI: 10.1128/IAI.70.12.7153-7155.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Cloning and Characterization of Genes Encoding Homologues of the B Subunit of Cholera Toxin and the Escherichia coli Heat-Labile Enterotoxin from Clinical Isolates of Citrobacter freundii and E. coli

Tadahiro Karasawa,1* Hideaki Ito,2 Teizo Tsukamoto,3 Shinji Yamasaki,4 Hisao Kurazono,5 Shah M. Faruque,6 G. Balakrish Nair,6 Mitsuaki Nishibuchi,7 and Yoshifumi Takeda4

Department of Bacteriology, Graduate School of Medical Science, Kanazawa University, 13-1 Takara-machi, Kanazawa 920-8640,1 Discovery Research Laboratories, Dainippon Pharmaceutical Co., Ltd., Suita, Osaka 564-0053,2 Osaka Prefectural Institute of Public Health, Higashinari-ku, Osaka, 537-0025,3 Research Institute, International Medical Center of Japan, Shinjyuku-ku, Tokyo 162-8640,4 Department of Medical Technology, School of Health Sciences, Okayama University, Okayama 700-8558,5 Center for Southeast Asian Studies, Kyoto University, Yoshida, Kyoto 606-8501, Japan,7 International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka 1212, Bangladesh6

Received 3 June 2002/ Returned for modification 31 July 2002/ Accepted 26 August 2002

We identified and characterized a gene encoding a homologue of the B subunits of cholera toxin (CTB) and heat-labile enterotoxin (LTB) of Escherichia coli from a clinical isolate of Citrobacter freundii that was found to produce a factor in the culture supernatant that cross-reacted with antibodies to CTB and LTB when assayed by enzyme-linked immunosorbent assay (ELISA). The gene encoding the ELISA-positive factor, cfxB, consisted of 375 nucleotides and was located downstream of an 852-nucleotide open reading frame, cfxA, with a 56-nucleotide intergenic space. The cfxB gene was predicted to encode a 125-amino-acid polypeptide, which had 73.8 and 72.8% identities with the amino acid sequences of LTB and CTB, respectively. However, the amino acid sequence of the deduced polypeptide CFXA had no homologies to those of the A subunits of CT or LT. DNA probes developed from the sequences of cfxA and cfxB were used to screen 67 C. freundii isolates and 152 E. coli isolates from diarrheal patients by colony blot hybridization. Two strains, C. freundii 48 and E. coli 176, reacted with both DNA probes under conditions of high stringency. We cloned homologues of the cfxA and cfxB genes from E. coli 176 and designated them ecxA and ecxB, respectively. The ecxA gene and the ecxB gene comprise 855 and 375 nucleotides, respectively, with a 50-nucleotide intergenic space, and encode a 285- and a 125-amino-acid residue polypeptides, respectively. The results of the present study may provide important clues to the origin and evolution of immunologically related factors sharing a common enterotoxin-like A and B subunit structures.

* Corresponding author. Mailing address: Department of Bacteriology, Graduate School of Medical Science, Kanazawa University, 13-1 Takara-machi, Kanazawa 920-8640, Japan. Phone: 81(76)265-2202. Fax: 81(76)234-4230. E-mail: karasawa{at}med.kanazawa-u.ac.jp.

Editor: J. T. Barbieri

Infection and Immunity, December 2002, p. 7153-7155, Vol. 70, No. 12
0019-9567/02/$04.00+0     DOI: 10.1128/IAI.70.12.7153-7155.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Alone, P. V., Malik, G., Krishnan, A., Garg, L. C. (2007). Deletion mutations in N-terminal {alpha}1 helix render heat labile enterotoxin B subunit susceptible to degradation. Proc. Natl. Acad. Sci. USA 104: 16056-16061 [Abstract] [Full Text]  


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