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Cyanobacterial phycobilisomes are made up from phycobiliproteins held together by linker proteins. Incident photons are absorbed by the phycobiliproteins that carry linear tetrapyrrole chromophores with extended conjugated bond systems. The chemical structure of the chromophores also bestows the phycobiliproteins with excellent radical scavenging and antioxidant properties and phycobiliproteins have pharmaceutical value as such. We purified and characterized the phycobilisome and its major protein constituent C-phycocyanin from the freshwater filamentous cyanobacterium Aphanizomenon gracile. Isolated phycobilisomes were shown to be intact and contained the phycobiliproteins allophyco-cyanin and C-phycocyanin, but not phycoerythrin, together with the classic set of linker proteins. C-phycocyanin could be easily purified and was of analytical grade with spectral characteristics similar to that of other cyanobacterial species. To our best knowledge, this is the first study to report the purification and characterization of the Aphanizomenon gracile phycobilisome and C-phycocyanin.

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., (© The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)