|PROSITE documentation PDOC50231|
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 (α, β and γ) 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 .
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 . The ricin B lectin domain has no major segments of a helix or β sheet but each of the QxW repeats contains an omega loop . 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 :
This profile is directed against part of the lambda linker and all of the three QxW repeats.Last update:
December 2001 / First entry.
PROSITE method (with tools and information) covered by this documentation:
|1||Authors||Hirabayashi J. Dutta S.K. Kasai K.|
|Title||Novel galactose-binding proteins in Annelida. Characterization of 29-kDa tandem repeat-type lectins from the earthworm Lumbricus terrestris.|
|Source||J. Biol. Chem. 273:14450-14460(1998).|
|2||Authors||Hazes B. Read R.J.|
|Title||A mosquitocidal toxin with a ricin-like cell-binding domain.|
|Source||Nat. Struct. Biol. 2:358-359(1995).|
|Title||The (QxW)3 domain: a flexible lectin scaffold.|
|Source||Protein Sci. 5:1490-1501(1996).|
|4||Authors||Rutenber E. Ready M. Robertus J.D.|
|Title||Structure and evolution of ricin B chain.|
|5||Authors||Rutenber E. Robertus J.D.|
|Title||Structure of ricin B-chain at 2.5 A resolution.|
|6||Authors||Shimoi H. Iimura Y. Obata T. Tadenuma M.|
|Title||Molecular structure of Rarobacter faecitabidus protease I. A yeast-lytic serine protease having mannose-binding activity.|
|Source||J. Biol. Chem. 267:25189-25195(1992).|
|7||Authors||Harris N. Peters L.L. Eicher E.M. Rits M. Raspberry D. Eichbaum Q.G. Super M. Ezekowitz R.A.|
|Title||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.|
|Source||Biochem. Biophys. Res. Commun. 198:682-692(1994).|