PROSITE documentation PDOC00248
Shiga/ricin ribosomal inactivating toxins active site signature


A number of bacterial and plant toxins act by inhibiting protein synthesis in eukaryotic cells. The toxins of the Shiga and ricin family inactivate 60S ribosomal subunits by an N-glycosidic cleavage which releases a specific adenine base from the sugar-phosphate backbone of 28S rRNA [1,2,3]. The toxins which are known to function in this manner are:

  • Shiga toxin from Shigella dysenteriae [4]. This toxin is composed of one copy of an enzymatically active A subunit and five copies of a B subunit responsible for binding the toxin complex to specific receptors on the target cell surface.
  • Shiga-like toxins (SLT) are a group of Escherichia coli toxins very similar in their structure and properties to Shiga toxin. The sequence of two types of these toxins, SLT-1 [5] and SLT-2 [6], is known.
  • Ricin, a potent toxin from castor bean seeds. Ricin consists of two glycosylated chains linked by a disulfide bond. The A chain is enzymatically active. The B chain is a lectin with a binding preference for galactosides. Both chains are encoded by a single polypeptidic precursor. Ricin is classified as a type-II ribosome-inactivating protein (RIP); other members of this family are agglutinin, also from castor bean, and abrin from the seeds of the bean Abrus precatorius [7].
  • Single chain ribosome-inactivating proteins (type-I RIP) from plants. Examples of such proteins are: barley protein synthesis inhibitors I and II, mongolian snake-gourd trichosanthin, sponge gourd luffin-A and -B, garden four-o'clock MAP, common pokeberry PAP-S and soapwort saporin-6 [7].

All these toxins are structurally related. A conserved glutamic residue has been implicated [8] in the catalytic mechanism; it is located near a conserved arginine which also plays a role in catalysis [9]. The signature we developed for these proteins includes these catalytic residues.

Last update:

December 2004 / Pattern and text revised.


Technical section

PROSITE method (with tools and information) covered by this documentation:

SHIGA_RICIN, PS00275; Shiga/ricin ribosomal inactivating toxins active site signature  (PATTERN)


1AuthorsEndo Y. Tsurugi K. Yutsudo T. Takeda Y. Ogasawara T. Igarashi K.
TitleSite of action of a Vero toxin (VT2) from Escherichia coli O157:H7 and of Shiga toxin on eukaryotic ribosomes. RNA N-glycosidase activity of the toxins.
SourceEur. J. Biochem. 171:45-50(1988).
PubMed ID3276522

2AuthorsMay M.J. Hartley M.R. Roberts L.M. Krieg P.A. Osborn R.W. Lord J.M.
TitleRibosome inactivation by ricin A chain: a sensitive method to assess the activity of wild-type and mutant polypeptides.
SourceEMBO J. 8:301-308(1989).
PubMed ID2714255

3AuthorsFunatsu G. Islam M.R. Minami Y. Sung-Sil K. Kimura M.
TitleConserved amino acid residues in ribosome-inactivating proteins from plants.
SourceBiochimie 73:1157-1161(1991).
PubMed ID1742358

4AuthorsStrockbine N.A. Jackson M.P. Sung L.M. Holmes R.K. O'Brien A.D.
TitleCloning and sequencing of the genes for Shiga toxin from Shigella dysenteriae type 1.
SourceJ. Bacteriol. 170:1116-1122(1988).
PubMed ID2830229

5AuthorsCalderwood S.B. Auclair F. Donohue-Rolfe A. Keusch G.T. Mekalanos J.J.
TitleNucleotide sequence of the Shiga-like toxin genes of Escherichia coli.
SourceProc. Natl. Acad. Sci. U.S.A. 84:4364-4368(1987).
PubMed ID3299365

6AuthorsJackson M.P. Neill R.J. O'Brien A.D. Holmes R.K. Newland J.W.
SourceFEMS Microbiol. Lett. 44:109-114(1987).

7AuthorsBarbieri L. Battelli M.G. Stirpe F.
TitleRibosome-inactivating proteins from plants.
SourceBiochim. Biophys. Acta 1154:237-282(1993).
PubMed ID8280743

8AuthorsHovde C.J. Calderwood S.B. Mekalanos J.J. Collier R.J.
TitleEvidence that glutamic acid 167 is an active-site residue of Shiga-like toxin I.
SourceProc. Natl. Acad. Sci. U.S.A. 85:2568-2572(1988).
PubMed ID3357883

9AuthorsMonzingo A.F. Collins E.J. Ernst S.R. Irvin J.D. Robertus J.D.
TitleThe 2.5 A structure of pokeweed antiviral protein.
SourceJ. Mol. Biol. 233:705-715(1993).
PubMed ID8411176

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