ISOLATION AND FUNCTIONAL STUDIES ON FUCOXANTHIN-CHLOROPHYLL PROTEIN FROM PHAEODACTYLUM TRICORNUTUM

In this study, we optimized the isolation method of fucoxanthin-chlorophyll protein (FCP) from Phaeodactylum tricornutum. The sequence, pigments and spectra of FCP were analyzed after the purification and homogenization of the protein. The sequence analysis showed that FCP consisted of 198 amino acids and the sequence shared 24% similarity with LHCII of higher plants. The mimic model predicted that similar to LHCII, FCP had three short transmembrane helixes but there was no helix on the membrane surface. We also found that FCP was associated with chlorophyll a, chlorophyll c and fucoxanthin, and the chl a/c ratio was 3.0. The absorption and fluorescence spectra demonstrated that fucoxanthin could absorb and transfer the green light energy to chlorophyll with high efficiency and thus provide sufficient energy in the low-light environment under the water. Moreover, the light energy at 400-500 nm was transferred by fucoxanthin with low efficiency, implying that fucoxanthin played a photo-protective role in response to strong lights. There are 4 conserved chlorophyll-binding sites in FCP; however, it was difficult to deter mine the fucoxanthin-binding sites due to the conformational change. This study laid a foundation for the further exploration of the structure and function of FCP.