The
lectin extracted from the seeds of Salvia sclarea (SSL) recognizes the
Tn antigen (GalNAc alpha1-->Ser/Thr) expressed in certain human
carcinomas. In previous studies, knowledge of the binding properties of SSL was restricted to GalNAcalpha1--> related
oligosaccharides and
glycopeptides. Thus, the requirements of functional groups in
monosaccharide and high-density polyvalent
carbohydrate structural units for SSL binding and an updated affinity profile were further evaluated by
enzyme-linked lectinosorbent (ELLSA) and inhibition assays. Among the
glycoproteins (gps) tested for interaction, a high density of exposed Tn-containing
glycoproteins such as in the armadillo salivary Tn
glycoprotein and asialo ovine salivary
glycoprotein reacted best with SSL. When the gps were tested for inhibition of SSL binding, which was expressed as 50% nanogram inhibition, the high density polyvalent Tn present in macromolecules was the most potent inhibitor. Among the
monosaccharide and
carbohydrate structural units studied, which were expressed as nanomole inhibition, GalNAc alpha1-->3GalNAc beta1-->3Gal alpha1-->4Gal beta1-->4Glc (Fp), GalNAc alpha1-->3Gal beta1-->4Glc (A(L)), GalNAc alpha1-->3GalNAc beta1-->Me (F beta), GalNAc alpha1-->3GalNAc alpha1-->Me (F alpha) and GalNAc alpha1--> Ser/Thr (Tn) were the most active
ligands, being 2.5-5.0 x 10(3) and 1.25-2.5 times more active than Gal and GalNAc, respectively. From the results, it is suggested that the combining site of SSL is a shallow groove type, recognizing the
monosaccharide of GalNAc as the major binding site or Tn up to the
Forssman pentasaccharide (Fp). It can be concluded that the three critical factors for SSL binding are the -NH CH(3)CO at carbon-2 in Gal, the configuration of carbon-3 in GalNAc, and the polyvalent Tn (GalNAc alpha1-->Ser/Thr) present in macromolecules. These results should assist in understanding the glyco-recognition factors involved in
carbohydrate-
lectin interactions in biological processes. The effect of the polyvalent F alpha, F beta and GalNAc beta1-->3Gal alpha1--> (P alpha) glycotopes on binding should be examined. However, this is hampered by the lack of availability of suitable
reagents.