β-Trefoil Lectins of the Family Mytilidae from a Comparative Perspective

Structural and functional differences are compared among lectins with β-trefoil folds, an essential and representative framework of proteins. The fundamental framework of this folding is the triple tandem repeat of subdomains consisting of 40 amino acids making four β-sheets to construct barrel and clover-shaped lid parts. Lectin databases UniLectin and TrefLec classified 12 categories of lectins with the β-trefoil fold in all biological domains and viruses. Each group appeared with a different proportion of distributions in each biological domain. SeviL and MytiLec represented β-trefoil lectins in the family Mytilidae. Nevertheless, each lectin had different primary structures, converging the same β-trefoil. The structural properties of MytiLec have also been shared with that of bacterial lectins. Furthermore, each mussel lectin bound to glycans of glycosphingolipid though the structures differed. Their glycan-binding properties seem to be helpful for a few applications of lectins because they recognized characteristic glycans relating to cell regulation of NK cells (GA1), auto-immune diseases (GM1b), cancers (Gb3), and regenerations (SSEA-1). Keywords: Lectin; β-trefoil fold; Mytilidae; SeviL; MytiLec