Post-translational cleavage pattern of Lupinus angustifolius γ-conglutin

A not-glycosylated isoform of γ-conglutin, a hexameric glycoprotein of Lupinus albus seed, participates in the oligomerization equilibrium

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.

Influence of temperature on secretion and functionality of lupin seed γ-conglutin

BACKGROUND

Basic 7S globulins, a group of proteins commonly found in legumes, undergo the intriguing phenomenon of release from the seeds into hot water. γ-Conglutin is a representative of this group of proteins found in lupin seeds. The physiological significance and the molecular mechanism of the selective release of γ-conglutin from lupin seeds remain unknown. Therefore, the presented study aimed to determine changes in the functionality of this protein in response to the high temperature occurring during lupin seed incubation.

RESULTS

It was confirmed that the main protein fraction released from the seeds during high-temperature incubation was γ-conglutin. The incubation condition favours the occurrence of this protein in a monomeric form, and the temperature used corresponds to its midpoint unfolding temperature. Subsequent analysis carried out on the γ-conglutin monomer revealed changes in its functionality after heat shock. The thermally treated protein shows a considerable increase in its interaction strength with flavonoids. Moreover, the inhibitory activity against glycoside hydrolases was enhanced when γ-conglutin monomer was exposed to specific temperatures.

CONCLUSION

The results of the present study provide a potential explanation of the physiological relevance of γ-conglutin and shed new light on a possible mechanism of its activation upon specific heat treatment. This knowledge will help characterise homologous proteins, which are commonly found in other legumes and undergo a similar heat-induced secretion phenomenon. © 2021 Society of Chemical Industry.

Narrow-Leafed Lupin (Lupinus angustifolius L.) Seeds Gamma-Conglutin is an Anti-Inflammatory Protein Promoting Insulin Resistance Improvement and Oxidative Stress Amelioration in PANC-1 Pancreatic Cell-Line

(1) Background: Inflammation molecular cues and insulin resistance development are some of the main contributors for the development and advance of the pathogenesis of inflammatory-related diseases; (2) Methods: We isolated and purified γ-conglutin protein from narrow-leafed lupin (NLL or blue lupin) mature seeds using affinity-chromatography to evaluate its anti-inflammatory activities at molecular level using both, a bacterial lipopolysaccharide (LPS)-induced inflammation and an insulin resistance pancreatic cell models; (3) Results: NLL γ-conglutin achieved a plethora of functional effects as the strong reduction of cell oxidative stress induced by inflammation through decreasing proteins carbonylation, nitric oxide synthesis and inducible nitric oxide synthase (iNOS) transcriptional levels, and raising glutathione (GSH) levels and modulation of superoxide dismutase (SOD) and catalase enzymes activities. γ-conglutin induced up-regulated transcriptomic and protein levels of insulin signalling pathway IRS-1, Glut-4, and PI3K, improving glucose uptake, while decreasing pro-inflammatory mediators as iNOs, TNFα, IL-1β, INFγ, IL-6, IL-12, IL-17, and IL-27; (4) Conclusion: These results suggest a promising use of NLL γ-conglutin protein in functional foods, which could also be implemented in alternative diagnosis and therapeutic molecular tools helping to prevent and treat inflammatory-related diseases.