Ribosome-inactivating protein abrin

Like ricin, abrin is a type 2 ribosome inactivating protein with A and B chains linked by a disulphide bond. The abrin A chain comprises 251 amino acid residues compared to 267 in the ricin A chain, both having three folding structural domains and a molecular weight of approximately 30 kDa. The abrin B chain has a molecular weight of 35 kDa with 60% of its amino acid residues identical to those of ricin s B chain. Both B chains have two saccharide binding sites which are highly conserved between the two toxins. 

Narayanan S, Surolia A and Karande AA (2004). Ribosome-inactivating protein and apoptosis abrin causes cell death via mitochondrial pathway in Jurkat cells. Biochem J, 377, 233-240. 

Mistletoe lectins have been extensively analyzed for their primary structure. Only the complete amino acid sequence of the A chain of mistletoe lectin 1 (VAA-1) has been determined thus far [25] but the data show a great homology with other ribosome inactivating proteins such as abrin a or ricin D with 111 and 103 amino acid residues conserved, respectively. 

Due to the extraordinary toxicity of intact ribosome-inactivating toxins like ricin, abrin, and modeccin, purification and handling of these proteins must be done with extreme care. Even dust from crude seed powders or lyophilized proteins should be considered dangerous. During... 

Shiga toxin produced by Shigella dysenteriae has similar structural features. The toxin binds to a glycolipid (Gb3), undergoes endocytosis, and the enzymatie Ai fragment, which is a specific N-glycosidase, removes adenine from one particular adenosine residue in the 28S RNA of the 60S ribosomal subunit. Removal of the adenine inactivates the 60S ribosome, blocking protein synthesis. Ricin, abrin, and a number of related plant proteins inhibit eukaryotic protein synthesis in a similar manner (Chapter 25). 

Abrin exerts its toxic action in the same way as ricin. The abrin B-chain avidly binds to a variety of cell types, in particular reticuloendothehal cells which bear the appropriate mannose receptors. The abrin B-chain also binds to the galactosyl-terminated receptors on the cell membrane to allow the entry of the abrin A-chain. Once internalized, the abrin A-chain is transported from the cell membrane to the ribosomes, where it catalytically inactivates the 60S ribosomal subunit by removing adenine from positions 4 and 324 of 28S rRNA, thereby inhibiting protein synthesis and causing cell death (Stripe and Barbieri, 1986). 

A group of plant lectins, such as abrin, ricin, and mod-eccin, are highly toxic to eukaryotic cells. Their mode of action consists of inhibition of protein synthesis by enzymatically inactivating the EF-2 binding region of the 60S ribosomal subunit, whereas the diphtheria toxin inactivates the EF-2 protein itself. Ricin is isolated from castor beans and has a molecular weight of 66,000. Like most plant and bacterial toxic proteins, ricin contains two... 

The binding, entry, and action of ricin, abrin, and modeccin on eukaryotic cellular systems have been reviewed.Modeccin binds to surface receptors containing terminal D-galactosyl residues, and like abrin and ricin it inhibits protein synthesis by inactivating the 60 S ribosomal sub-units. Competition experiments with various glycoproteins have indicated that the modeccin receptors are different from abrin receptors. Mutant cell lines resistant to abrin and ricin were not resistant to modeccin and vice-versa. 

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