Lipid-induced quenching of chlorophyll singlet excitation in lipid-nanodisc accommodated FCP complex from diatom Chaetoceros gracilis

Diatom is the most flourishing group of ocean photosynthetic organism, whose living success relies largely on the light-harvesting and photoprotection potency of its antenna complex, i.e. the fucoxanthin chlorophyll (Chl) a/c binding protein (FCP). With reference to the light-harvesting antennae of higher plants and green algae, FCP binds weakly coupled Chls, among which the intra-complex excitation energy transfer (EET) is more susceptive to the protein conformation and surrounding. Particularly, the fucoxanthin molecules bound in FCP are highly interactive with the thylakoid membrane, which may influence the intra-complex EET processes. To investigate the effect of lipid microenvironment on the conformation and the energetics of FCP, we reconstituted Chaetoceros gracilis FCP dimer into L-alpha-PC lipid nanodisc, and investigated the fluorescence dynamics among different pools of Chls using time-resolved fluorescence spectroscopy. The lipid-protein interactions lead to obvious conformational change of the blue-absorbing fucoxanthin molecule, and about 30 % decrease in Chl a-fluorescence quantum yield and 20 % shortening in fluorescence lifetime, which is ascribed to the quenching of major fluorescent component at 677 nm by non-radiative quencher.