Anti-α-galactoside and Anti-β-glucoside Antibodies are Partially Occupied by Either of Two Albumin-bound O-glycoproteins and Circulate as Ligand-binding Triplets

Karthi Sreedevi, Sabarinath P. Subramanian, Geetha Mandagini, Padinjaradath S. Appukuttan

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


Two heavily O-glycosylated proteins and albumin co-purified with anti-α-galactoside (anti-Gal), the chief xenograft-rejecting antibody and anti-β-glucan (ABG) antibody isolated from human plasma by affinity chromatography on respective ligand-bearing matrices. Both antibodies and O-glycoproteins co-purified with plasma albumin eluted from albumin-specific matrix. Using components of affinity-purified antibody samples separated by electrophoresis binding of either albumin or antibody to the affinity matrix of the other or binding of O-glycoprotein to either matrix was ruled out. Enzyme-linked immunoassay and ligand-induced fluorescence enhancement of fluorolabeled antibody showed that O-glycoproteins occupied sugar-binding sites of anti-Gal and ABG. Neither antibody recognized albumin. O-Glycoprotein-albumin complexes free in plasma, or released from antibodies by specific sugars, were captured on microwell-coated O-glycan-specific lectin jacalin and detected using labeled anti-albumin. We conclude that circulating anti-Gal and ABG form protein triplets in which either O-glycoprotein bridges between antibody and albumin by binding simultaneously to both. Bound albumin restricted O-glycoprotein occupation on antibodies enabling triplets to bind other ligands using spared binding sites. Free anti-Gal and ABG were undetectable in plasma. Jacalin treatment, but not de-O-glycosylation of O-glycoproteins abolished their recognition by anti-Gal or ABG indicating that antibodies recognized serine- and threonine-rich peptide sequences that underlie the O-glycans and are reported surrogate ligands for anti-Gal. The albumin- and antibody-binding O-glycoproteins AOP1 and AOP2 were single polypeptide proteins of size 107 kDa and 98 kDa, containing 54% and 51% carbohydrate respectively and conformed to no known plasma protein in properties. Prospects of triplet-mediated modulations in autologous tissues expressing antibody ligands are discussed.

Original languageEnglish (US)
Pages (from-to)222-241
Number of pages20
JournalImmunological Investigations
Issue number3
StatePublished - Apr 3 2019
Externally publishedYes


  • Albumin- and antibody-associated O-glycosylated protein
  • anti-carbohydrate antibody-O-glycoprotein-albumin triplet
  • anti-α-galactoside antibody
  • anti-β-glucoside antibody
  • serine- and threonine-rich peptide sequence

ASJC Scopus subject areas

  • Immunology


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