Structural characterisation of the native fetuin-binding protein Scilla campanulata agglutinin: a novel two-domain lectin

The three-dimensional structure of a 244-residue, multivalent, fetuin-bindi ng lectin, SCAfet, isolated from bluebell (Scilla campanulata) bulbs, has b een solved at 3.3 Angstrom resolution by molecular replacement using the co ordinates of the 119-residue, mannose-binding lectin, SCAman, also from blu ebell bulbs. Unlike most monocot mannose-binding lectins, such as Galanthus nivalis agglutinin from snowdrop bulbs, which fold into a single domain, S CAfet contains two domains with approximately 55% sequence identity, joined by a linker peptide. Both domains are made up of a 12-stranded beta-prism II fold, with three putative carbohydrate-binding sites, one on each subdom ain. SCAfet binds to the complex saccharides of various animal glycoprotein s but not to simple sugars. (C) 2000 Federation of European Biochemical Soc ieties.