Abstract
A previously uncharacterized protein with a carotenoid-binding function has been isolated and characterized from the gonad of the New Zealand sea urchin Evechinus chloroticus. The main carotenoid bound to the protein was determined by reversed phase-high performance liquid chromatography to be 9′-cis-echinenone and hence this 15 kDa protein has been called an echinenone-binding protein (EBP). Purification of the EBP in quantity from the natural source proved to be challenging. However, analysis of EBP by mass spectrometry combined with information from the Strongylocentrotus purpuratus genome sequence and the recently published E. chloroticus transcriptome database, enabled recombinant expression of wild type EBP and also of a cysteine61 to serine mutant that had improved solubility characteristics. Circular dichroism data and ab initio structure prediction suggests that the EBP adopts a 10-stranded β-barrel fold consistent with that of fatty acid-binding proteins. Therefore, EBP may represent the first report of a fatty acid-binding protein in complex with a carotenoid.
Highlights
For over 100 years the sea urchin has been established as an important biological model organism
The method for the purification of carotenoid-binding proteins (CBPs) from gonad tissue was adapted from Jouni and Wells [39]
Removal of lipid appeared to result in loss of some carotenoids, due to the association of carotenoids with lipoproteinlike complexes [71]
Summary
For over 100 years the sea urchin has been established as an important biological model organism. A simple body plan and the relative ease of reproductive manipulation have made the sea urchin a popular animal for the study of reproduction and development [1,2,3]. In addition to this service to biology, sea urchins have provided a valuable food resource to coastal populations around the world since prehistoric times [4]. Export market values of the product are dependent upon taste and texture but with particular importance placed on color for attractive culinary presentation [7]. Yellow/orange colored gonads are the most desirable [7] and can attain up to US$400/Kg [8], undesirable shades such as brown and black are common amongst E. chloroticus [5,6], which adversely affects the market value
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