Evechinus chloroticus (Kina), a species of sea urchin endemic to New Zealand, are harvested commercially as their edible roe (gonad) is considered a delicacy on both local and international markets. However, the revenue attained by the roe is proportional to the desirability of pigmentation, which appears to be due to varying quantities of carotenoids chemically modified in and transported from the viscera via protein interactions. Carotenoid-binding proteins (CBPs) are likely to have several important roles in roe pigmentation including acting as metabolic enzymes, cell surface receptors, transmembrane transporters and the stabilisation of carotenoids deposited in the tissue.

A putative CBP, which is tightly associated with echinenone has been identified and partially purified from the roe of E. chloroticus. The protein, approximately 12 kDa in size, has been analysed by mass spectrometry and putatively identified as a hypothetical protein with homology to other known CBPs.  The DNA sequence corresponding to the protein was identified in an mRNA library assembled for analysis of the Kina transcriptome. The mRNA sequence was used to design unique primers for cDNA synthesis, the PCR product of which was inserted into a pET 28a plasmid (Novagen) containing an N-terminal poly histidine tag. The plasmid was then transformed into Escherichia coli BL21 (DE3) cell line for protein expression. The purified protein will be use for in vitro carotenoid binding assays as well as structural studies.

To further investigate the role of proteins in roe pigmentation; proteomic profiles of E. chloroticus and Heliocidarius erthrogamma (an Australian sea urchin which exhibits less variability in roe colouration) will be produced using Large-format 2-D polyacrylamide electrophoresis. Image analysis software will be used detect differences in the profiles and proteins of interest will be analysed by mass spectrometry.