This Article Full Text (PDF) Other Versions of this Article: IAI.01546-06v1 75/5/2189    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Shimizu, T. Articles by Noda, M. Search for Related Content PubMed PubMed Citation Articles by Shimizu, T. Articles by Noda, M.

 Previous Article  |  Next Article 

Infect. Immun. doi:10.1128/IAI.01546-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Serine 31 residue of B subunit of Shiga toxin 2 is essential for the secretion in Enterohemorrhagic Escherichia coli

Department of Molecular Infectiology, Graduate School of Medicine, Chiba University, 1-8-1 Inohana, Chiba, 260-8670; Department of Infection Biology, Graduate School of Comprehensive Human Sciences, University of Tsukuba, 1-1-1 Ten-nohdai, Tsukuba, 305-8575; Department of Infectious Diseases, Research Institute, International Medical Center of Japan, 1-21-1 Toyama, Shinjuku-ku, Tokyo, 162-8655; Kotobiken Medical Laboratories, 445-1 Kamiyokoba, Tsukuba, 305-0854

^* To whom correspondence should be addressed. Email: tshimizu{at}faculty.chiba-u.jp.

	Abstract

Shiga toxins (Stxs) produced by enterohemorrhagic Escherichia coli (EHEC) include shiga toxin 1 (Stx1) as well as shiga toxin 2 (Stx2). Stx1 is cell-associated, whereas Stx2 is localised to the culture supernatant. We have analysed the secretion of Stx2 by generating histidine-tagged StxB (StxBH). Although neither Stx1BH nor Stx2BH was secreted in StxBH-overexpressed EHEC, Stx2BH-overexpressed EHEC showed inhibited Stx2 secretion. On the other hand, Stx1BH-overexpressed EHEC showed no alteration of Stx2 secretion. B subunit chimeras of Stx1 and Stx2 were used to identify the specific residue of Stx2B that the Stx2 secretory system recognises. Alteration of the serine 31 residue to an asparagine residue (S31N) in Stx2BH enabled the recovery of Stx2 secretion. On the other hand, alteration of the asparagine 32 residue to a serine residue (N32S) in Stx1BH caused partial secretion of a point-mutated histidine-tagged B subunit in EHEC. Based on the evidence, it appeared possible that this residue might contain secretion-related information for Stx2 secretion. To investigate this hypothesis, we constructed isogenic mutant strains, Stx1 (B subunit, N32S)-producing EHEC and Stx2 (B subunit, S31N)-producing EHEC. Although the mutant Stx2 was cell-associated in isogenic mutant EHEC, the mutant Stx1 was not extracellular. However, when we used plasmids for the expression of the mutant holotoxins, the overexpressed mutant Stx1 was found in the supernatant fraction and the overexpressed mutant Stx2 was found in the cell-associated fraction in the mutant holotoxin gene-transformed EHEC. These results indicate that the serine 31 residue of the B subunit of Stx2 contains secretion-related information.