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Crystal structure of the A-subunit of the AB5 toxin from E. coliCrystal structure of the A-subunit of the AB5 toxin from E. coli
Structural highlights
FunctionSUBA_ECOLX Protease subunit of subtilase cytotoxin SubAB5 (PubMed:17024087). An endoprotease specific for host endoplasmic reticulum (ER) chaperone BiP/HSPA5, has no activity on human HSP70 or HSPA8 (PubMed:17024087). Cleaves between 'Leu-416' and 'Leu-417' of BiP/HSPA5 in the hinge between BiP's ATPase and protein-binding domains (PubMed:17024087). This induces host ER stress response and eventual cell death (PubMed:18005237, PubMed:18433465). Culture supernatant of E.coli expressing both subA and subB are toxic for Vero cells (African green monkey kidney cell line), Chinese hamster ovary cells and Hct-8 cells (human colonic epithelial cell line); the subunits are not toxic individually (PubMed:15226357). Purified SubAB5 is highly toxic, <0.1 pg is able to kill at least 50% of 30'000 Vero cells in a microtiter plate assay after 3 days; no cytotoxicity is seen at 24 hours (PubMed:15226357). Preabsorption with cells expressing a ganglioside GM2 mimic reduced cytotoxicity of SubAB5 by 93% in the Vero cytotoxicity assay (PubMed:15226357). Intraperitoneal injection of 200 ng of purified SubAB5 kills mice; the higher the dose the faster the mice die. Animals injected intraperitoneally with purified SubAB5 have microvascular thrombi in the brain and other organs, including the renal tubules and glomeruli (PubMed:15226357). Injection induces an unfolded response in mice (PubMed:17024087). Mice fed E.coli cells expressing cloned SubAB5 experience drastic weight loss and appear ill and lethargic (PubMed:15226357). Protein synthesis in Vero cells is transiently inhibited by SubAB5; both subunits are required for this effect (PubMed:17101670, PubMed:18005237, PubMed:18433465). Inhibition of protein synthesis is prevented by brefeldin A; cells are arrested in the G1 phase (PubMed:18005237). SubAB5 at 100 ng/ml induced caspase-dependent apoptosis in Vero cells through mitochondrial membrane damage (PubMed:19380466).[1] [2] [3] [4] [5] [6] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedAB5 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. AB5 subtilase cytotoxin inactivates the endoplasmic reticulum chaperone BiP.,Paton AW, Beddoe T, Thorpe CM, Whisstock JC, Wilce MC, Rossjohn J, Talbot UM, Paton JC Nature. 2006 Oct 5;443(7111):548-52. PMID:17024087[7] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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