title: A defence-related Olea europaea β-glucosidase hydrolyses and activates oleuropein into a potent protein cross-linking agent.
abstract: Oleuropein, the major secoiridoid compound in olive, is involved in a sophisticated two-component defence system comprising a β-glucosidase enzyme that activates oleuropein into a toxic glutaraldehyde-like structure. Although oleuropein deglycosylation studies have been monitored extensively, an oleuropein β-glucosidase gene has not been characterized as yet. Here, we report the isolation of OeGLU cDNA from olive encoding a β-glucosidase belonging to the defence-related group of terpenoid-specific glucosidases. In planta recombinant protein expression assays showed that OeGLU deglycosylated and activated oleuropein into a strong protein cross-linker. Homology and docking modelling predicted that OeGLU has a characteristic (β/α)8 TIM barrel conformation and a typical construction of a pocket-shaped substrate recognition domain composed of conserved amino acids supporting the β-glucosidase activity and non-conserved residues associated with aglycon specificity. Transcriptional analysis in various olive organs revealed that the gene was developmentally regulated, with its transcript levels coinciding well with the spatiotemporal patterns of oleuropein degradation and aglycon accumulation in drupes. OeGLU upregulation in young organs reflects its prominent role in oleuropein-mediated defence system. High gene expression during drupe maturation implies an additional role in olive secondary metabolism, through the degradation of oleuropein and reutilization of hydrolysis products.
authors.affiliation: Department of Biotechnology, Agricultural University of Athens, 118 55 Athens, Greece.
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Koudounas
authors.affiliation: Department of Biotechnology, Agricultural University of Athens, 118 55 Athens, Greece Department of Oenology and Beverage Technology, Technological Educational Institute of Athens, 12210 Athens, Greece.
authors.forename: Georgios
authors.initials: G
authors.lastname: Banilas
authors.affiliation: Department of Biotechnology, Agricultural University of Athens, 118 55 Athens, Greece University of Nicosia Research Foundation, University of Nicosia, 1700 Nicosia, Cyprus.
authors.forename: Christos
authors.initials: C
authors.lastname: Michaelidis
authors.affiliation: University of Nicosia Research Foundation, University of Nicosia, 1700 Nicosia, Cyprus.
authors.forename: Catherine
authors.initials: C
authors.lastname: Demoliou
authors.affiliation: Department of Biotechnology, Agricultural University of Athens, 118 55 Athens, Greece.
authors.forename: Stamatis
authors.initials: S
authors.lastname: Rigas
authors.affiliation: Department of Biotechnology, Agricultural University of Athens, 118 55 Athens, Greece phat@aua.gr.
authors.forename: Polydefkis
authors.initials: P
authors.lastname: Hatzopoulos
mesh_terms: D001483:Base Sequence; D005638:Fruit / Q000201:enzymology / Q000235:genetics; D015870:Gene Expression; D006868:Hydrolysis; D057888:Iridoid Glucosides; D039823:Iridoids / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D031658:Olea / Q000201:enzymology* / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA; D013729:Terpenes / Q000378:metabolism; D019076:Transgenes; D001617:beta-Glucosidase / Q000235:genetics / Q000378:metabolism*
chemical_list: D057888:Iridoid Glucosides; D039823:Iridoids; D010940:Plant Proteins; D013729:Terpenes; C002769:oleuropein; D001617:beta-Glucosidase
keywords: heterologous expression; oleuropein; olive development; plant defence; protein cross-linking.; β-Glucosidase