Multivalent human blood group ABH and Lewis glycotopes are key recognition factors for a lFuc>Man binding lectin from phytopathogenic Ralstonia solanacearum

Abstract

Ralstonia solanacearum lectin (RSL), that might be involved in phytopathogenicity, has been defined as lFuc≫Man specific. However, the effects of polyvalency of glycotopes and mammalian structural units on binding have not been established. In this study, recognition factors of RSL were comprehensively examined with natural multivalent glycotopes and monomeric ligands using enzyme linked lectin-sorbent and inhibition assays. Among the glycans tested, RSL reacted strongly with multivalent blood group A h (GalNAcα1–3[Fucα1–2]Gal) and H (Fucα1–2Gal) active glycotopes, followed by B h (Galα1–3[Fucα1–2]Gal), Le a (Galβ1–3[Fucα1–4]GlcNAc) and Le b (Fucα1–2Galβ1–3[Fucα1–4]GlcNAc) active glycotopes. But weak or negligible binding was observed for blood group precursors having Galβ1–3/4GlcNAcβ1- ( I β/ II β) residues or Galβ1–3GalNAcα1- ( T α), GalNAcα1-Ser/Thr ( Tn) bearing glycoproteins. These results indicate that the density and degree of exposure of multivalent ligands of α1–2 linked lFuc to Gal at the non-reducing end is the most critical factor for binding. An inhibition study with monomeric ligands revealed that the combining site of RSL should be of a groove type to fit trisaccharide binding with highest complementarity to blood group H trisaccharide ( H L; Fucα1–2Galβ1–4Glc). The outstandingly broad RSL saccharide-binding profile might be related to the unusually wide spectrum of plants that suffer from R. solanacearum pathogenicity and provide ideas for protective antiadhesion strategies.