PROSITE documentation PDOC50228

SUEL-type lectin domain profile

Lectins bind to specific carbohydrate residues of glycoproteins and glycolipids present at the cell surface. This allow them to agglutinate a variety of cellular types. On the basis of sequence similarity and common characteristics such as sugar binding specificity, conserved carbohydrate recognition domains, and ion requirement the different lectins can be grouped in different categories, like C-type, I-type, galectins, pentraxins and P-type lectin.

The sea urchin (Anthocidaris crassispina) egg lectin (SUEL) forms a new class of lectins. Altough SUEL was first isolated as a D-galactoside binding lectin it was latter shown that it bind to L-rhamnose preferentially [1,2]. L-rhamnose and D-galactose share the same hydroxyl group orientation at C2 and C4 of the pyranose ring structure. SUEL is a lectin that exist as a disulfide linked homodimer. The dimeric form is essential for hemagglutination activity but the monomeric form retains carbohydrate binding capacity [1]. Based on primary structure analysis, a cysteine-rich domain homologous to the SUEL protein has been identified in the following proteins [3,4,5]:

• Plant β-galactosidases (EC 3.2.1.23) (lactases). They constitute a widespread family of enzymes characterized by their ability to hydrolyse terminal, non-reducing β D-galactosyl residues from β-D-galactosides.
• Mammalian latrophilin, the calcium independent receptor of α- latrotoxin (CIRL). It belongs to the secretin family of G-protein coupled receptors. The lectin domain is not required for α-latratoxin binding [5].
• Human lectomedin-1.
• Rhamnose-binding lectin (SAL) from catfish (Parasilurus asotus) eggs. This protein is composed of three tandem repeat domains homologous to the SUEL lectin domain. All cysteine positions of each domain are completely conserved [2].
• Caenorhabditis elegans hypothetical proteins B0457.1, F32A7.3A and F32A7.3B.
• Human hypothetical protein KIAA0821.