The ricin B-type lectin domain is a carbohydrate-binding domain formed from presumed gene triplication. It shows a beta-trefoil fold characterized by 12 beta strands folded into three similar trefoil subdomains (alpha, beta, and gamma) associated to give an overall structure with pseudo-3-fold symmetry. The ricin B-type lectin domain was originally found in Ricin, which is a legume lectin from the seeds of the castor bean plant, Ricinus communis. It is also found in many carbohydrate-recognition proteins like plant and bacterial AB-toxins, glycosidases, or proteases, which serve diverse functions such as inhibitory toxicity, enzymatic activity, and signal transduction. The ricin B-type lectin domain can be present in one or more copies and has been shown in some instances to bind simple sugars, such as galactose or lactose. The most characteristic, though not completely conserved, sequence feature is the presence of a Q-W pattern. Consequently, the ricin B-type lectin domain has also been referred as the (QxW)3 domain and the three homologous regions as the QxW repeats. A disulfide bond is also conserved in some QxW repeats.
Structure:1V6W; Streptomyces Olivaceoviridis endo-1,4-beta-d-xylanase in complex with 2(2)-4-O-methyl-alpha-D-glucuronosyl-xylobiose, contacts at 4A - View structure with Cn3D
Jiyao W et al.(2023). "The conserved domain database in 2023.",