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AB5 subtilase cytotoxin inactivates the endoplasmic reticulum chaperone BiP


AB5 toxins are produced by pathogenic bacteria and consist of enzymatic A subunits that corrupt essential eukaryotic cell functions, and pentameric B subunits that mediate uptake into the target cell. AB5 toxins include the Shiga, cholera and pertussis toxins and a recently discovered fourth family, subtilase cytotoxin, which is produced by certain Shiga toxigenic strains of Escherichia coli. Here we show that the extreme cytotoxicity of this toxin for eukaryotic cells is due to a specific single-site cleavage of the essential endoplasmic reticulum chaperone BiP/GRP78. The A subunit is a subtilase-like serine protease; structural studies revealed an unusually deep active-site cleft, which accounts for its exquisite substrate specificity. A single amino-acid substitution in the BiP target site prevented cleavage, and co-expression of this resistant protein protected transfected cells against the toxin. BiP is a master regulator of endoplasmic reticulum function, and its cleavage by subtilase cytotoxin represents a previously unknown trigger for cell death.

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Figure 1: SubAB cleaves BiP in Vero cells.
Figure 2: Co-localization of SubAB and BiP.
Figure 3: In vivo cleavage of BiP and induction of CHOP, and in vitro cleavage of purified BiP.
Figure 4: Structural comparison of SubA with subtilisin Carlsberg.
Figure 5: Expression of SubAB-resistant BiP D416 prevents cytotoxicity.


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We thank M.-J. Gething and L. Helfenbaum for materials and advice, J. Wallace for discussions and L. Zaker-Tabrizi for technical assistance. This research was supported by a Program Grant from the Australian National Health and Medical Research Council (NHMRC) (to A.W.P and J.C.P). J.R. is supported by an Australian Research Council Professorial and Federation Fellowship and T.B. by a NHMRC Peter Doherty Fellowship. C.M.T is supported by grants from the National Institutes of Health, USA. Author Contributions A.W.P. designed, performed and interpreted experiments, and contributed to writing the manuscript. T.B., J.C.W., M.C.J.W. and J.R. crystallized SubA, solved the structure and contributed to manuscript preparation. C.M.T. contributed to experimental design and interpretation and writing of the manuscript. U.M.T. performed experiments. J.C.P. contributed to design and interpretation of experiments, project management and writing of the manuscript.

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Correspondence to Adrienne W. Paton or James C. Paton.

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The coordinates and structure factors for SubA have been deposited in the Protein Data Bank and assigned the deposition code 2iy9. Reprints and permissions information is available at The authors declare that they have no competing financial interests.

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Paton, A., Beddoe, T., Thorpe, C. et al. AB5 subtilase cytotoxin inactivates the endoplasmic reticulum chaperone BiP. Nature 443, 548–552 (2006).

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