About the Lectin
Two hemagglutinins with different carbohydrate specificities have been isolated from gorse seeds. The two lectins, UEA-I and UEA-II, can be separated from crude extracts by salt or ethanol precipitation. Both have been sequenced and are homologous with each other, and also homologous with other legume lectins of various specificities 1 . Carbohydrate-binding peptides have been isolated for each lectin after peptidase digestion, and these peptides also exhibit homology with other such peptides 2,3 . UEA-I interacts specifically with blood group H type 2 antigen 4 , which is expressed in individuals with type O blood and to a lesser degree in individuals with type A or B blood. While the nominal specificity of UEA-I for fucose is similar to the lectins from Lotus tetragonolobus and Anguilla anguilla, there are some subtle differences in its binding to more complex carbohydrates 5 . UEA-I reacts strongly with α(1,2) linked fucose residues but poorly or not at all with α(1,3) or α(1,6)-linked fucose 6 . UEA-I is unable to bind internal fucose structures 7 and the presence of an internal α(1,3)-linked fucose on the H type 2 oligosaccharide decreases lectin affinity for this blood group antigen 3-fold 8 . The carbohydrate binding site of the lectin is somewhat extended. UEA-I recognizes not only the specific fucose linkage, but the linkages of the subterminal carbohydrates as well. The H type 2 trisaccharide Fuc α(1,2)Gal β(1,4) GlcNAc is a potent inhibitor of the lectin but the H type 1 trisaccharide Fuc α(1,2)Gal β(1,3) GlcNAc is 400 times less inhibitory. Additionally, the H type 2 trisaccharide is approximately 200 times more inhibitory than the disaccharide, Fuc α(1,2)Gal 8 . UEA-I has been used as a marker for vascular endothelium 9 and subsequently used to identify endotheilial cells of benign vascular lesions more specifically than antibodies to Factor VII-related antigen 10 . UEA-I coated magnetic beads have been used to isolate endothelial cells associated with microvessels for subsequent cell culture 11 . The lectin has been used to identify malignant tumors of endothelial origin 12 . UEA-I has been used to differentiate between angiosarcomas and epithelial tumors 13 ; however, blood group antigens are found in a variety of tissues 14 , so it may be more accurate to use specific monoclonal antibodies 15 . UEA-I is also a marker for incompletely differentiated gastrin cells 16 , specifically stains muscle cells in certain myopathies 17 , and UEA-I-coated microspheres specifically interact with mouse Peyer’s patch M-cells 18 . Reports on the molecular weight of UEA-I vary. It is generally considered to be a dimer of 60-68,000 Da, although a lower value of 45,000 Da was observed when the lectin was analyzed on Ultragel ACA34 19 . When analyzed by SDS-PAGE at EY Laboratories, the two subunits are stained by Coomassie blue, as well as an occasional band of 45-50,000 Da. UEA-I has been crystallized and preliminary X-ray diffraction data reported 20 .
UEA-II is specific for oligomers of β(1,4)-linked GlcNAc, accommodating up to four carbohydrate residues 21 . The monosaccharide GlcNAc is not an inhibitor of lectin activity. UEA-II contains a high percentage of Ca ++ which is required for binding. Treatment of the lectin with EDTA abolishes agglutinating activity, although activity returns with the addition of calcium. Although the lectin requires calcium for binding, it is still active in phosphate buffer without added ions. UEA-II is not blood group specific but the best inhibitors are the H type oligosaccharides, Fuc α(1,2)Gal β(1,4)GlcNAc and Fuc α(1,2)Gal β(1,4)Glc. A third lectin, UEA-III, which is specific for lactose, has also been isolated from gorse seeds 22 .
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- Goldstein, I. J. and Poretz, R. D. (1986) in: The Lectins: Properties, Functions and Applications in Biology and Medicine. (Liener, I.E., Sharon, N., and Goldstein, I. J. eds) Academic Press. pg 33-248 (Table XXVI).
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Product Characteristics – UEA I
|Buffer||0.01M Phosphate – 0.15M NaCl, pH 7.2-7.4.|
|Blood Group||O (H).|
|Activity||Less than 4 μg/ml will agglutinate human type O erythrocytes.
Less than 0.5 μg/ml will agglutinate neuraminidase treated erythrocytes.
|Molecular Weight||Aggregate MW=60-68,000. Two major bands of MW=28,000 and 30,000 by SDS-PAGE.
Occasionally a band of MW=45-50,000 will also stain.
Product Characteristics – UEA II
|Buffer||0.01M Phosphate – 0.15M NaCl, pH 7.2-7.4.|
|Activity||Less than 30 μg/ml will agglutinate human type O erythrocytes.|
|Inhibitory Carbohydrate||GlcNAcβ(1,4) GlcNAc.|
|Molecular Weight||Aggregate MW=110,000. A single band of MW= 30,000 by SDS-PAGE.|