Galactose/rhamnose-binding lectin domain is formed from a four-stranded antiparallel beta-sheet which packs against an alpha-helix. It was originally described as galactose-binding lectin domain since it was found in a galactose-binding sea urchin egg lectin (SUEL). SUEL was first isolated as a D-galactoside binding lectin, it was later shown that it binds to L-rhamnose preferentially. Galactose/rhamnose-binding lectin domain is also found in many rhamnose-binding lectins, such as Oncorhynchus keta L-rhamnose-binding lectins (CSLs) and Silurus asotus rhamnose-binding lectin (SAL). In addition, the superfamily includes many SUEL/CSLs/SAL homologous proteins, such as plant beta-galactosidases, mammalian latrophilins, Caenorhabditis elegans protein EVA-1 and its homolog, human protein EVA-1 homolog C (also known as C21orf63). Due to the lack of galactose/rhamnose-binding key residues, some superfamily members may not form a binding pocket for galactose/rhamnose. Therefore, they are unlikely to act as galactose/rhamnose-binding lectins.
Jiyao W et al.(2023). "The conserved domain database in 2023.",