Carbohydrate specificity of an insecticidal lectin isolated from the leaves of Glechoma hederacea (ground ivy) towards mammalian glycoconjugates

Tanuja Singh, June H. Wu, Willy J. Peumans, Pierre Rougé, Els J.M. Van Damme, Richard A. Alvarez, Ola Blixt, Albert M. Wu*

*Corresponding author for this work

Research output: Contribution to journalJournal Article peer-review

38 Scopus citations

Abstract

Preliminary studies indicated that the potent insecticidal lectin, Gleheda, from the leaves of Glechoma hederacea (ground ivy) preferentially agglutinates human erythrocytes carrying the Tn (GalNAcα1-Ser/Thr) antigen. However, no details have been reported yet with respect to the fine specificity of the lectin. To corroborate the molecular basis of the insecticidal activity and physiological function of Gleheda, it is necessary to identify the recognition factors that are involved in the Gleheda-glycotope interaction. In the present study, the requirement of high-density multivalent carbohydrate structural units for Gleheda binding and a fine-affinity profile were evaluated using ELLSA (enzyme-linked lectinosorbent assay) with our extended glycan/ligand collections, a glycan array and molecular modelling. From the results, we concluded that a high-density of exposed multivalent Tn-containing glycoproteins (natural armadillo and asialo ovine salivary glycoproteins) were the most potent factors for Gleheda binding. They were, on a nanogram basis, 6.5 × 105, 1.5 × 104 and 3.1 × 103 times more active than univalent Gai (galactose), Gal-NAc(N-acetylgalactosamine) and Tn respectively. Among mono- and oligo-saccharides examined, simple clustered Tn (molecular mass < 3000 Da) from ovine salivary glycoprotein was the best, being 37.5 and 1.7 × 103 times better than GalNAc and Gal respectively. GalNAc glycosides were significantly more active than Gal glycosides, indicating that the N-acetamido group at C-2 plays an important role in Gleheda binding. The results of glycan array support the conclusions drawn with respect to the specificity of Gleheda based on the ELLSA assays. These findings combined with the results of the molecular modelling and docking indicate the occurrence of a primary GalNAcα1-binding site in the Gleheda monomer. However, the extraordinary binding feature of Gleheda for glycoproteins demonstrates the importance of affinity enhancement by high-density multivalent glycotopes in the ligand-lectin interactions in biological processes.

Original languageEnglish
Pages (from-to)331-341
Number of pages11
JournalBiochemical Journal
Volume393
Issue number1
DOIs
StatePublished - 01 01 2006

Keywords

  • Carbohydrate specificity
  • Combining site
  • Gleheda
  • Glycoprotein binding
  • Lectin
  • Multivalency

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