{PDOC50231} {PS50231; RICIN_B_LECTIN} {BEGIN} ****************************************** * Lectin domain of ricin B chain profile * ****************************************** 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 [1,2,3]. 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 [4,5]. 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 [2,3]. A disulfide bond is also conserved in some of the QxW repeats [2]. 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 [4]. 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 [5]. 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. Some proteins containing a ricin B lectin domain are listed below [3]: - Ricin, from Ricinus communis (Castor bean). Ricin belongs to a group of plant AB-toxins, which also contains agglutinin and abrin. Ricin is composed of a sugar-binding subunit (B chain) that attaches to galactose residues presented by cell surface glycoproteins or glycolipids and a subunit (chain A) with enzymatic activity that attacks and inactivates ribosomes. The B chain contains two ricin B lectin domains [4]. - Serine protease I (RPI) (EC 3.4.21.-), from Rarobacter faecitabidus [6]. RIP is a serine protease exhibiting lytic activity toward living yeast cells. It possess a ricin B lectin domain that is involved in mannose binding in its C terminal part. - The bacterial AHH1/ASH4/HlyA/VVHA family of hemolysins. Bacterial hemolysins are exotoxins that attack blood cell membranes and cause cell rupture by mechanisms not clearly defined. Proteins belonging to this family possess one ricin B lectin domain. - Glucan endo-1,3-beta-glucanase (EC 3.2.1.39), from Oerskovia xanthineolytica. This yeast-lytic protein has a C-terminal ricin B lectin domain which appears to target the catalytic domain to yeast cell wall. - Endo-1,4-beta-xylanase A (EC 3.2.1.8) (gene xlnA), from Streptomyces. The C-terminal ricin B lectin domain has been proposed to bind to the polymeric substrate of this enzyme, but no carbohydrate binding data are available. - The macrophage mannose receptor (MRC1), from mammals. MRC1 is a Type I membrane receptor protein that is expressed at the surface of mature macrophages. It binds mannose- and fucose-rich carbohydrate polymers and appears to mediate phagocytic uptake of foreign microorganisms. Its extracellular region contains 8 copies of the C-type lectin domain (see ) and one ricin B lectin domain to which no sugar binding function has been ascribed so far [7]. - The AIM1 protein, from mammals. AIM1 is a member of the beta- gamma- crystallin superfamily and contains a C-terminal ricin B lectin domain. In human, it is associated with the control of tumorigenicity. - Phospholipase A2 receptor, from mammals. This proteins contains 8 copies of the C-type lectin domain and one N-terminal ricin B lectin domain whose function is unknown. - UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase (EC 2.4.1.41) (gene GALNT1). This protein catalyzes the initial reaction in O-linked oligosaccharide biosynthesis, the transfer of an N-acetyl-D-galactosamine residue to a serine or threonine residue on the protein receptor. This protein binds carbohydrate as a soluble substrate and contains one copy of the ricin B lectin domain. - The 33-kDa hemagglutinin component of the botulinum neurotoxin complex. This protein has two copies of the ricin B lectin domain and agglutinates red blood cells. -Sequences known to belong to this class detected by the profile: ALL. -Other sequence(s) detected in Swiss-Prot: NONE. -Note: This profile is directed against part of the lambda linker and all of the three QxW repeats. -Last update: December 2001 / First entry. [ 1] Hirabayashi J., Dutta S.K., Kasai K. "Novel galactose-binding proteins in Annelida. Characterization of 29-kDa tandem repeat-type lectins from the earthworm Lumbricus terrestris." J. Biol. Chem. 273:14450-14460(1998). PubMed=9603958 [ 2] Hazes B., Read R.J. "A mosquitocidal toxin with a ricin-like cell-binding domain." Nat. Struct. Biol. 2:358-359(1995). PubMed=7664090 [ 3] Hazes B. "The (QxW)3 domain: a flexible lectin scaffold." Protein Sci. 5:1490-1501(1996). PubMed=8844840 [ 4] Rutenber E., Ready M., Robertus J.D. "Structure and evolution of ricin B chain." Nature 326:624-626(1987). PubMed=3561502; DOI=10.1038/326624a0 [ 5] Rutenber E., Robertus J.D. "Structure of ricin B-chain at 2.5 A resolution." Proteins 10:260-269(1991). PubMed=1881882 [ 6] Shimoi H., Iimura Y., Obata T., Tadenuma M. "Molecular structure of Rarobacter faecitabidus protease I. A yeast-lytic serine protease having mannose-binding activity." J. Biol. Chem. 267:25189-25195(1992). PubMed=1339445 [ 7] Harris N., Peters L.L., Eicher E.M., Rits M., Raspberry D., Eichbaum Q.G., Super M., Ezekowitz R.A. "The exon-intron structure and chromosomal localization of the mouse macrophage mannose receptor gene Mrc1: identification of a Ricin-like domain at the N-terminus of the receptor." Biochem. Biophys. Res. Commun. 198:682-692(1994). 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