A distinctive pathway for triplet-triplet energy transfer photoprotection in fucoxanthin chlorophyll-binding proteins from Cyclotella meneghiniana

Fucoxanthin chlorophyll-binding proteins (FCPs) are the major light-harvesting complexes of diatoms. In this work, FCPs isolated from Cyclotella meneghiniana have been studied by means of optically detected magnetic resonance (ODMR) and time-resolved electron paramagnetic resonance (TR-EPR), with the aim to characterize the photoprotective mechanism based on triplet-triplet energy transfer (TTET). The spectroscopic properties of the chromophores carrying the triplet state have been interpreted on the basis of a delved analysis of the recently solved crystallographic structures of FCP. The results point toward a photoprotective role for two fucoxanthin molecules exposed to the exterior of the FCP monomers. This shows that FCP has adopted a structural strategy different from that of related light-harvesting complexes from plants and other microalgae, in which the photoprotective role is carried out by two highly conserved carotenoids in the interior of the complex.

Automated summary

In this study, the fucoxanthin chlorophyll-binding proteins (FCPs) from Cyclotella meneghiniana were investigated using optically detected magnetic resonance (ODMR) and time-resolved electron paramagnetic resonance (TR-EPR) to characterize the photoprotective mechanism based on triplet-triplet energy transfer (TTET). The results show that two fucoxanthin molecules exposed to the exterior of the FCP monomers play a photoprotective role, indicating a structural strategy different from related light-harvesting complexes from plants and other microalgae.