The domain within your query sequence starts at position 460 and ends at position 590; the E-value for the RICIN domain shown below is 4.29e-31.

WGEIRNVGTGLCTDTKLGTLGSPLRLETCIRGRGEAAWNSMQVFTFTWREDIRPGDPQHT
KKFCFDAVSHTSPVTLYDCHSMKGNQLWKYRKDKTLYHPVSGSCMDCSESDHRVFMNTCN
PSSLTQQWLFE

RICIN

Ricin-type beta-trefoil

• SMART accession number: SM00458
• Description: Carbohydrate-binding domain formed from presumed gene triplication.
• Interpro abstract (IPR000772):

  Ricin is a legume lectin from the seeds of the castor bean plant, Ricinus communis. The seeds are poisonous to people, animals and insects and just one milligram of ricin can kill an adult.

  Primary structure analysis has shown the presence of a similar domain in many carbohydrate-recognition proteins like plant and bacterial AB-toxins, glycosidases or proteases [ (PUBMED:9603958) (PUBMED:7664090) (PUBMED:8844840) ]. This domain, known as the ricin B lectin domain, can be present in one or more copies and has been shown in some instance to bind simple sugars, such as galactose or lactose.

  The ricin B lectin domain is composed of three homologous subdomains of 40 amino acids (alpha, beta and gamma) and a linker peptide of around 15 residues (lambda). It has been proposed that the ricin B lectin domain arose by gene triplication from a primitive 40 residue galactoside-binding peptide [ (PUBMED:3561502) (PUBMED:1881882) ]. The most characteristic, though not completely conserved, sequence feature is the presence of a Q-W pattern. Consequently, the ricin B lectin domain as also been refered as the (QxW) ₃ domain and the three homologous regions as the QxW repeats [ (PUBMED:7664090) (PUBMED:8844840) ]. A disulphide bond is also conserved in some of the QxW repeats [ (PUBMED:7664090) ].

  The 3D structure of the ricin B chain has shown that the three QxW repeats pack around a pseudo threefold axis that is stabilised by the lambda linker [ (PUBMED:3561502) ]. The ricin B lectin domain has no major segments of a helix or beta sheet but each of the QxW repeats contains an omega loop [ (PUBMED:1881882) ]. An idealized omega-loop is a compact, contiguous segment of polypeptide that traces a 'loop-shaped' path in three-dimensional space; the main chain resembles a Greek omega.

There are 38185 RICIN domains in 35446 proteins in SMART's nrdb database.

Literature (relevant references for this domain)

Primary literature is listed below; Automatically-derived, secondary literature is also avaliable.

• Hazes B
• The (QxW)3 domain: a flexible lectin scaffold.
• Protein Sci. 1996; 5: 1490-501

Lectins form a class of proteins that have evolved a specialized carbohydrate-binding function. Based on amino acid sequence analysis, several lectin families have been described and a lectin domain, the (QxW)3 domain, was discussed recently based on 11 family members. In this paper, the (QxW)3 domain family is extended to 45 sequences, several of which have very low sequence identity with the previously known members of the family. A hidden Markov model was used to identify the most divergent members of the family. The expanded set of sequences gives us a more complete appreciation of the conserved features, and the lack thereof, in this lectin family. This, in turn, provides new insights in the structural and functional properties of the individual family members.

• Smith PD, Moss SE
• Structural evolution of the annexin supergene family.
• Trends Genet. 1994; 10: 241-6

The annexin family of calcium-binding proteins is comprised of at least ten mammalian genes, with additional representatives in lower eukaryotes. Recent structural analyses of several annexin genes have provided insights into the relationship between exon organization and functional domains. We discuss the implications of these findings and speculate on the evolutionary origins of the annexin supergene family.

• Robertus J
• The structure and action of ricin, a cytotoxic N-glycosidase.
• Semin Cell Biol. 1991; 2: 23-30

The X-ray structure of the heterodimeric plant cytotoxin ricin has been elucidated. The A chain, known to be a specific N-glycosidase, has a prominent active site cleft. The B chain is a two domain lectin, which arose from the replication of a primitive sugar binding peptide. The molecular model reveals residues which are likely to be important in the action of the protein. Site directed mutagenesis reveals the relative importance of a number of these groups. A model for the mechanism of the A chain, including steric strain of the scissile bond and carboxonium ion transition state stabilization is proposed.

• Rutenber E, Ready M, Robertus JD
• Structure and evolution of ricin B chain.
• Nature. 1987; 326: 624-6

Ricin is a dimeric toxin from the castor bean Ricinus communis, which is composed of a sugar-binding subunit (B) that attaches to receptors on the surfaces of target cells and a subunit (A) with enzymatic activity that attacks and inactivates ribosomes. We report here that comparison of amino-acid sequence data with high-resolution structure analysis of the ricin B subunit shows it to be the product of a series of gene duplications. The modern protein has two sugar-binding domains, each of which is composed of three copies of a more ancient galactose-binding peptide of about 40 residues.

• Villafranca JE, Robertus JD
• Ricin B chain is a product of gene duplication.
• J Biol Chem. 1981; 256: 554-6

The cytotoxin ricin is a heterodimer composed of an A chain which enzymatically inhibits protein synthesis on eukaryotic ribosomes and a lectin B chain which binds to cell surfaces and triggers uptake of the toxin. A low resolution (4 A) x-ray structure revealed that the B chain is a bilobal structure and that each domain binds a galactose sugar. These apparent structural similarities suggested that the protein might have internal symmetry and might have arisen by gene duplication. A subsequent search of the amino acid sequence provided strong evidence for homology between th NH2- and COOH-terminal halves of the B chain and suggested that they may have arisen from a common ancestor. There is no strong relationship between the halves of the A chain and little, if any, significant sequence homology between the A and B chains of ricin.

Metabolism (metabolic pathways involving proteins which contain this domain)

% proteins involved	KEGG pathway ID	Description
48.20	map00512	O-Glycan biosynthesis
48.20	map01030	Glycan structures - biosynthesis 1
0.90	map00600	Sphingolipid metabolism
0.45	map00520	Nucleotide sugars metabolism
0.45	map00530	Aminosugars metabolism
0.45	map00603	Glycosphingolipid biosynthesis - globoseries
0.45	map00561	Glycerolipid metabolism
0.45	map00052	Galactose metabolism
0.45	map01032	Glycan structures - degradation

This information is based on mapping of SMART genomic protein database to KEGG orthologous groups. Percentage points are related to the number of proteins with RICIN domain which could be assigned to a KEGG orthologous group, and not all proteins containing RICIN domain. Please note that proteins can be included in multiple pathways, ie. the numbers above will not always add up to 100%.

Structure (3D structures containing this domain)

3D Structures of RICIN domains in PDB

PDB code	Title
1abr	CRYSTAL STRUCTURE OF ABRIN-A
1ce7	MISTLETOE LECTIN I FROM VISCUM ALBUM
1dqg	CRYSTAL STRUCTURE OF THE CYSTEINE RICH DOMAIN OF MANNOSE RECEPTOR
1dqo	Crystal structure of the cysteine rich domain of mannose receptor complexed with Acetylgalactosamine-4-sulfate
1fwu	CRYSTAL STRUCTURE OF THE CYSTEINE-RICH DOMAIN OF MANNOSE RECEPTOR COMPLEXED WITH 3-SO4-LEWIS(X)
1fwv	CRYSTAL STRUCTURE OF THE CYSTEINE-RICH DOMAIN OF MANNOSE RECEPTOR COMPLEXED WITH 3-SO4-LEWIS(A)
1ggp	CRYSTAL STRUCTURE OF TRICHOSANTHES KIRILOWII LECTIN-1 AND ITS RELATION TO THE TYPE 2 RIBOSOME INACTIVATING PROTEINS
1hwm	EBULIN,ORTHORHOMBIC CRYSTAL FORM MODEL
1hwn	EBULIN COMPLEXED WITH GALACTOSE, TRIGONAL CRYSTAL FORM
1hwo	EBULIN COMPLEXED WITH LACTOSE, TRIGONAL CRYSTAL FORM
1hwp	EBULIN COMPLEXED WITH PTEROIC ACID, TRIGONAL CRYSTAL FORM
1isv	Crystal structure of xylanase from Streptomyces olivaceoviridis E-86 complexed with xylose
1isw	Crystal structure of xylanase from Streptomyces olivaceoviridis E-86 complexed with xylobiose
1isx	Crystal structure of xylanase from Streptomyces olivaceoviridis E-86 complexed with xylotriose
1isy	Crystal structure of xylanase from Streptomyces olivaceoviridis E-86 complexed with glucose
1isz	Crystal structure of xylanase from Streptomyces olivaceoviridis E-86 complexed with galactose
1it0	Crystal structure of xylanase from Streptomyces olivaceoviridis E-86 complexed with lactose
1knl	Streptomyces lividans Xylan Binding Domain cbm13
1knm	Streptomyces lividans Xylan Binding Domain cbm13 in Complex with Lactose
1m2t	Mistletoe Lectin I from Viscum album in Complex with Adenine Monophosphate. Crystal Structure at 1.9 A Resolution
1mc9	STREPROMYCES LIVIDANS XYLAN BINDING DOMAIN CBM13 IN COMPLEX WITH XYLOPENTAOSE
1onk	Mistletoe lectin I from viscum album
1oql	Mistletoe Lectin I from Viscum album complexed with galactose
1pc8	Crystal Structure of a novel form of mistletoe lectin from Himalayan Viscum album L. at 3.8A resolution
1pum	Mistletoe lectin I in complex with galactose
1puu	Mistletoe lectin I in complex with lactose
1qxm	Crystal structure of a hemagglutinin component (HA1) from type C Clostridium botulinum
1rzo	Agglutinin from Ricinus communis with galactoaza
1sz6	MISTLETOE LECTIN I FROM VISCUM ALBUM. CRYSTAL STRUCTURE AT 2.05 A RESOLUTION
1tfm	CRYSTAL STRUCTURE OF A RIBOSOME INACTIVATING PROTEIN IN ITS NATURALLY INHIBITED FORM
1v6u	Crystal Structure Of Xylanase From Streptomyces Olivaceoviridis E-86 Complexed With 2(2)-alpha-L-arabinofuranosyl-xylobiose
1v6v	Crystal Structure Of Xylanase From Streptomyces Olivaceoviridis E-86 Complexed With 3(2)-alpha-L-arabinofuranosyl-xylotriose
1v6w	Crystal Structure Of Xylanase From Streptomyces Olivaceoviridis E-86 Complexed With 2(2)-4-O-methyl-alpha-D-glucuronosyl-xylobiose
1v6x	Crystal Structure Of Xylanase From Streptomyces Olivaceoviridis E-86 Complexed With 3(3)-4-O-methyl-alpha-D-glucuronosyl-xylotriose
1vcl	Crystal Structure of Hemolytic Lectin CEL-III
1xez	Crystal Structure Of The Vibrio Cholerae Cytolysin (HlyA) Pro-Toxin With Octylglucoside Bound
1xhb	The Crystal Structure of UDP-GalNAc: polypeptide alpha-N-acetylgalactosaminyltransferase-T1
1xyf	ENDO-1,4-BETA-XYLANASE FROM STREPTOMYCES OLIVACEOVIRIDIS
1ybi	Crystal structure of HA33A, a neurotoxin-associated protein from Clostridium botulinum type A
1yf8	Crystal structure of Himalayan mistletoe RIP reveals the presence of a natural inhibitor and a new functionally active sugar-binding site
2aai	CRYSTALLOGRAPHIC REFINEMENT OF RICIN TO 2.5 ANGSTROMS
2d1z	Crystal structure of catalytic-site mutant xylanase from Streptomyces olivaceoviridis E-86
2d20	Crystal structure of michaelis complex of catalytic-site mutant xylanase from Streptomyces olivaceoviridis E-86
2d22	Crystal structure of covalent glycosyl-enzyme intermediate of catalytic-site mutant xylanase from Streptomyces olivaceoviridis E-86
2d23	Crystal structure of EP complex of catalytic-site mutant xylanase from Streptomyces olivaceoviridis E-86
2d24	Crystal structure of ES complex of catalytic-site mutant xylanase from Streptomyces olivaceoviridis E-86
2d7i	Crsytal structure of pp-GalNAc-T10 with UDP, GalNAc and Mn2+
2d7r	Crystal structure of pp-GalNAc-T10 complexed with GalNAc-Ser on lectin domain
2dry	Crystal structure of the earthworm lectin C-terminal domain mutant
2drz	Crystal structure of the earthworm lectin C-terminal domain mutant in complex with lactose
2ds0	Crystal structure of the earthworm lectin C-terminal domain mutant in complex with 6'-sialyllactose
2e4m	Crystal structure of hemagglutinin subcomponent complex (HA-33/HA-17) from Clostridium botulinum serotype D strain 4947
2ffu	Crystal Structure of Human ppGalNAcT-2 complexed with UDP and EA2
2ffv	Human ppGalNAcT-2 complexed with manganese and UDP
2mll	MISTLETOE LECTIN I FROM VISCUM ALBUM
2q3n	Agglutinin from Abrus Precatorius (APA-I)
2r9k	Crystal Structure of Misteltoe Lectin I in Complex with Phloretamide
2rg9	Crystal structure of viscum album mistletoe lectin I in native state at 1.95 A resolution, comparison of structure active site conformation in ricin and in viscumin
2rst	NMR structure of the C-terminal domain of EW29
2vlc	Crystal structure of Natural Cinnamomin (Isoform III)
2vsa	Structure and mode of action of a mosquitocidal holotoxin
2vse	Structure and mode of action of a mosquitocidal holotoxin
2z48	Crystal Structure of Hemolytic Lectin CEL-III Complexed with GalNac
2z49	Crystal Structure of Hemolytic Lectin CEL-III Complexed with methyl-alpha-D-galactopylanoside
2zqn	Crystal structure of the earthworm R-type lectin C-half in complex with Lactose
2zqo	Crystal structure of the earthworm R-type lectin C-half in complex with GalNAc
2zr1	Agglutinin from Abrus Precatorius
3a07	Crystal Structure of Actinohivin; Potent anti-HIV Protein
3a21	Crystal Structure of Streptomyces avermitilis beta-L-Arabinopyranosidase
3a22	Crystal Structure of beta-L-Arabinopyranosidase complexed with L-arabinose
3a23	Crystal Structure of beta-L-Arabinopyranosidase complexed with D-galactose
3ah1	HA1 subcomponent of botulinum type C progenitor toxin complexed with N-acetylneuramic acid
3ah2	HA1 subcomponent of botulinum type C progenitor toxin complexed with N-acetylgalactosamine
3ah4	HA1 subcomponent of botulinum type C progenitor toxin complexed with galactose
3aj5	HA1 (HA33) subcomponent of botulinum type C progenitor toxin complexed with N-acetylgalactosamine, bound at site II
3aj6	HA1 (HA33) mutant F179I of botulinum type C progenitor toxin complexed with N-acetylgalactosamine, bound at site II
3c9z	Sambucus nigra agglutinin II (SNA-II), tetragonal crystal form
3ca0	Sambucus nigra agglutinin II (SNA-II), hexagonal crystal form
3ca1	Sambucus nigra agglutinin II (SNA-II)- tetragonal crystal form- complexed to galactose
3ca3	Crystal structure of Sambucus Nigra Agglutinin II (SNA-II)-tetragonal crystal form- complexed to N-Acetylgalactosamine
3ca4	Sambucus nigra agglutinin II, tetragonal crystal form- complexed to lactose
3ca5	Crystal structure of Sambucus nigra agglutinin II (SNA-II)-tetragonal crystal form- complexed to alpha1 methylgalactose
3ca6	Sambucus nigra agglutinin II (SNA-II)- tetragonal crystal form- complexed to Tn antigen
3cah	Sambucus nigra aggutinin II. tetragonal crystal form- complexed to fucose
3d7w	Mistletoe Lectin I in Complex with Zeatin
3o44	Crystal Structure of the Vibrio cholerae Cytolysin (HlyA) Heptameric Pore
3o5w	Binding of kinetin in the active site of mistletoe lectin I
3pg0	Crystal structure of designed 3-fold symmetric protein, ThreeFoil
3rti	Crystal structure of ricin bound with formycin monophosphate
3rtj	Crystal structure of ricin bound with dinucleotide ApG
3vsf	Crystal structure of 1,3Gal43A, an exo-beta-1,3-Galactanase from Clostridium thermocellum
3vsz	Crystal structure of Ct1,3Gal43A in complex with galactan
3vt0	Crystal structure of Ct1,3Gal43A in complex with lactose
3vt1	Crystal structure of Ct1,3Gal43A in complex with galactose
3vt2	Crystal structure of Ct1,3Gal43A in complex with isopropy-beta-D-thiogalactoside
3w9t	pore-forming CEL-III
3win	Clostridium botulinum Hemagglutinin
3wmy	Crystal Structure of Streptomyces coelicolor alpha-L-arabinofuranosidase
3wmz	Crystal Structure of Streptomyces coelicolor alpha-L-arabinofuranosidase ethylmercury derivative
3wn0	Crystal Structure of Streptomyces coelicolor alpha-L-arabinofuranosidase in complex with L-arabinose
3wn1	Crystal Structure of Streptomyces coelicolor alpha-L-arabinofuranosidase in complex with xylotriose
3wn2	Crystal Structure of Streptomyces coelicolor alpha-L-arabinofuranosidase in complex with xylohexaose
4d0t	4D0T
4d0z	4D0Z
4d11	4D11
4den	Structural insightsinto potent, specific anti-HIV property of actinohivin; Crystal structure of actinohivin in complex with alpha(1-2) mannobiose moiety of high-mannose type glycan of gp120
4eb2	Crystal structure Mistletoe Lectin I from Viscum album in complex with n-acetyl-d-glucosamine at 1.94 A resolution.
4end	Crystal structure of anti-HIV actinohivin in complex with alpha-1,2-mannobiose (P 2 21 21 form)
4g1r	Crystal structure of anti-HIV actinohivin in complex with alphs-1,2-mannobiose (Form II)
4hr6	Crystal structure of snake gourd (Trichosanthes anguina) seed lectin, a three chain homologue of type II RIPs
4ion	Macrolepiota procera ricin B-like lectin (MPL)
4iyb	Macrolepiota procera ricin B-like lectin (MPL) in complex with galactose
4izx	Macrolepiota procera ricin B-like lectin (MPL) in complex with lactose
4j2s	Macrolepiota procera ricin B-like lectin (MPL) in complex with Di-LacNAc
4jkx	Crystal structure Mistletoe Lectin I from Viscum album in complex with kinetin at 2.35 A resolution.
4jp0	Crystal structure of Cry35Ab1
4lo0	Apo HA17-HA33
4lo1	HA17-HA33-Gal
4lo2	HA17-HA33-Lac
4lo3	HA17-HA33-LacNac
4lo7	HA70(D3)-HA17-HA33
4ouj	4OUJ
4owj	4OWJ
4owk	4OWK
4owl	4OWL
4p6a	4P6A
4qd2	4QD2
4z8s	4Z8S
4z9w	4Z9W
4za3	4ZA3
4zbv	4ZBV
4zfu	4ZFU
4zfw	4ZFW
4zfy	4ZFY
4zgr	4ZGR
4zlb	4ZLB
5ajn	5AJN
5ajo	5AJO
5ajp	5AJP
5ao5	5AO5
5ao6	5AO6
5b2h	5B2H
5bp5	5BP5
5bqu	5BQU
5e4k	5E4K
5e4l	5E4L
5ew6	5EW6
5fv9	5FV9

Links (links to other resources describing this domain)

• PFAM: Ricin_B_lectin
• INTERPRO: IPR000772
• PROSITE: SHIGA_RICIN