genegodbold
commented
1 year ago Bacterial
- Shiga toxin subunit A (StxA) from Escherichia coli: The catalytic Stx1 A subunit is noncovalently associated with 5 Stx1 B subunits [PMID:14638419]. The catalytic A subunit of Stx1 is an N-glycosidase and enzymatically inactivates ribosomes, preventing protein synthesis (translation) which eventually kills the cell. This is accomplished by depurination of an adenine residue at position 4324 on the 28S RNA of the 60S subunit [PMID:1324134]. The sole difference between Stx and Stx1 is a single amino acid in the A subunit of the protein [PMID:14638419]. The median lethal dose for the Shigatoxin in monkeys is about 1 ng/kg when administered intravenously. Guinea pigs and mice are approximately 1000 fold more resistant to the toxin [PMID:6806598].
- Shiga toxin subunit A (StxA) from Shigella (multiple species): (same information)
Plants (obviously, these are not in a symbiont-host relationship)
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Abrin from Abrus precatorius: The abrin B chain of 33 kDa is linked to the catalytic A chain of 30 kDa by a disulfide bond. The abrin B polypeptide is a lectin that binds to cell surface carbohydrates. This binding leads to internalization of the abrin complex through receptor-mediated endocytosis [PMID:29027937]. Abrin is a type II ribosome-inactivating protein. Abrin is an N-glycosidase that cuts the C-N bond of adenine at position 4324 on the 28S ribosomal RNA thereby disallowing elongation factors 1 and 2 from binding to the ribosome [PMID:29027937]. The median lethal dose (LD50) for abrin in humans is between 10 and 1000 micrograms per kg via ingestion and is 3.3 micrograms per kg if injected intravenously [PMID:19239732].
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Volkensin from Adenia volkensii: Volkensin is taken up into HeLa cells though at lower levels than nigrin b and ricin [PMID:15289938]. The B chain of volkensin preferentially binds to sugars containing galactose. Volkensin is translated as a 523 residue protein that is later split into A and B chains. It is a type II ribosome-inactivating protein. The A chain consists of 250 residues, two cysteines, and inactivates yeast ribosomes via its RNA N-glycosidase activity. The B chain is 258 residues in length, contains 12 cysteines, and is nearly 50% identical to the B chain of ricin D. Based on the similarity to ricin, it is hypothesized that Cys245 of the A chain is linked to Cys4 of the B chain. The catalytic residues of the A chain appear conserved in volkensin relative to ricin with Tyr74, Tyr113, Glu162, and Arg165 involved in catalysis [PMID:14686924].
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Ricin from Ricinus communis (Castor bean plant): Ricin is a type II ribosomal inhibitor protein (RIP). The toxin targets the 28S ribosomal RNA of eukaryotic cells. By cleaving an adenosine residue in an exposed loop it prevents the binding of elongation factor and inactivates the ribosome. The ricin A chain is catalytic and can completely inactivate 1500 ribosomes per minute, thereby disabling translation and killing the cell. The B chain of the ricin protein associates with the catalytic A chain through a disulfide bond. The B chain adheres to carbohydrate residues on eukaryotic cells. Following binding to a cell, ricin can enter via both receptor-mediated and adsorptive-mediated endocytosis. Ricin moves from early endosomes to the trans-Golgi network then undergoes retrograde vesicular transport through the Golgi. Ricin is then carried to the ER by calreticulin where the disulfide bond is reduced and the catalytic chain enters the cytosol via the Sec61p translocon. The unfolded A chain avoids ubiquitination because of its low lysine content and it refolds into its biologically active conformation [PMID:28722977].
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Nigrin b (Sambucus nigra agglutinin V; SNAV) from Sambucus nigra (European elder): Nigrin b is a type II ribosome-inactivating protein consisting of two peptide chains linked by a disulfide bond. The B chain of nigrin b binds to GalNAc ligands and mediates endocytosis into mammalian cells [PMID:8647092].
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Trichosanthin from Trichosanthes kirilowii: TCS is an RNA N-glycosidase, a type I ribosome-inactivating protein (RIP) that depurinates adenine-4324 of mammalian 28S rRNA. TCS can be cytotoxic at high levels but it cannot easily enter cells because it lacks a lectin entry domain like ricin. However it can apparently enter cells at a low level, perhaps through electrostatic interactions with cell membranes followed by endocytosis via clathrin-coated vesicles [PMID:30127254].
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Mistletoe Lectin 1 (and 2 and 3 and 4) from Viscum album: The ribosomal inhibitor protein (type II), viscumin is cleaved into an A chain and a larger B chain linked by disulfide bonds. The A chain of viscumin inhibits translation by catalytically inactivating the ribosome [PMID:7142144]. The A chain of the mistletoe lectin inactivates the ribosomes by cleaving a N-glycosidic bond at A-4324 of 28 S rRNA in the ribosomes (similar to the A chain of ricin) [PMID:3360143]. The B chain lectin binds preferentially to galactose-containing glycolipids or glycoproteins on the surface of cells [PMID:16508080]. The median lethal dose (LD50) of purified viscumin for mice following intraperitoneal administration is ~5 micrograms/kg. Up to 40 mg of purified viscumin can be obtained from 100 grams of mistletoe leaves [PMID:6130311].
pgaudet
For GO-PATHGO alignment PATHGO:0000030 mediates ribosome inactivation in another organism @genegodbold to provide references
Noting that we have 'related' viral terms: GO:0039604 suppression by virus of host translation