Further characterization of the combining sites of Bandeiraea (Griffonia) simplicifolia lectin-I, isolectin A(4)

Bandeiraea (Griffonia) simplicifolia lectin-I, isolectin A(4) (GS I-A,), wh ich is cytotoxic to the human colon cancer cell lines, is one of two lectin families derived from its seed extract. It contains only a homo-oligomer o f subunit A, and is most specific for GalNAc alpha 1-->. In order to elucid ate the GS I-A(4)-glycoconjugate interactions in greater detail, the combin ing site of this lectin was further characterized by enzyme linked lectino- sorbent assay (ELLSA) and by inhibition of lectin-glycoprotein interactions . This study has demonstrated that the Tn-containing glycoproteins tested, consisting of mammalian salivary glycoproteins (armadillo, asialo-hamster s ublingual, asialo-ovine, -bovine, and -porcine submandibular), are bound st rongly by GS I-A(4). Among monovalent inhibitors so far tested, p-NO2-pheny l alpha GalNAc is the most potent, suggesting that hydrophobic forces are i mportant in the interaction of this lectin, GS IA, is able to accommodate t he monosaccharide GalNAc at the nonreducing end of oligosaccharides. This s uggests that the combining site of the lectin is a shallow cavity, among ol igosaccharides and monosaccharides tested as inhibitors of the binding of G S I-A(4), the hierarchy of potencies are: GalNAc alpha 1-->3GalNAc beta 1-- >3Gal alpha 1-->4Gal beta 1-->4Glc (Forssman pentasaccharide) > GalNAc alph a 1-->3(LFuc alpha 1-->2)Gal (blood group A) > GalNAc > Gal alpha 1-->4Gal > Gal alpha 1-->3Gal (blood group B-like) > Gal.