γ-conglutin (γ-C) is a hexameric glycoprotein accumulated in lupin seeds and has long been considered as a storage protein. Recently, it has been investigated for its possible postprandial glycaemic regulating action in human nutrition and for its physiological role in plant defence. The quaternary structure of γ-C results from the assembly of six monomers in reversible pH-dependent association/dissociation equilibrium. Our working hypothesis was that the γ-C hexamer is made up of glycosylated subunits in association with not-glycosylated isoforms, that seem to have ‘escaped’ the correct glycosylation process in the Golgi. Here we describe the isolation of not-glycosylated γ-C monomers in native condition by two in tandem lectin-based affinity chromatography and the characterization of their oligomerization capacity. We report, for the first time, the observation that a plant multimeric protein may be formed by identical polypeptide chains that have undergone different post-translational modifications. All obtained considered, the results strongly suggest that the not-glycosylated isoform can also take part in the oligomerization equilibrium of the protein. •A not-glycosylated γ-C monomers from the native protein has been isolated for the first time.•Native γ-C is a hexamer made up by both glycosylated and not-glycosylated monomers.•The seed glycoprotein is formed by identical polypeptide chains that have undergone different PTMs.•The not-glycosylated polypeptide is able to take part in the oligomerization equilibrium of γ-C.