Spectral Tuning and Excitation-Energy Transfer by Unique Carotenoids in Diatom Light-Harvesting Antenna

• Published in: Journal of the American Chemical Society Vol. 146; no. 6; pp. 3984 - 3991
• Main Authors: Fujimoto, Kazuhiro J., Seki, Takuya, Minoda, Takumi, Yanai, Takeshi
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 14.02.2024
• Subjects: Carotenoids - chemistry; Chlorophyll - chemistry; Chlorophyll A; Chlorophyll Binding Proteins - chemistry; Chlorophyll Binding Proteins - metabolism; Cryoelectron Microscopy; Diatoms - chemistry; Energy Transfer; Light-Harvesting Protein Complexes - chemistry; Protein Subunits - metabolism; Xanthophylls
• ISSN: 0002-7863; 1520-5126; 1520-5126
• DOI: 10.1021/jacs.3c12045

The light-harvesting antennae of diatoms and spinach are composed of similar chromophores; however, they exhibit different absorption wavelengths. Recent advances in cryoelectron microscopy have revealed that the diatom light-harvesting antenna fucoxanthin chlorophyll a/c-binding protein (FCPII) forms a tetramer and differs from the spinach antenna in terms of the number of protomers; however, the detailed molecular mechanism remains elusive. Herein, we report the physicochemical factors contributing to the characteristic light absorption of the diatom light-harvesting antenna based on spectral calculations using an exciton model. Spectral analysis reveals the significant contribution of unique fucoxanthin molecules (fucoxanthin-S) in FCPII to the diatom-specific spectrum, and further analysis determines their essential role in excitation-energy transfer to chlorophyll. It was revealed that the specificity of these fucoxanthin-S molecules is caused by the proximity between protomers associated with the tetramerization of FCPII. The findings of this study demonstrate that diatoms employ fucoxanthin-S to harvest energy under the ocean in the absence of long-wavelength sunlight and can provide significant information about the survival strategies of photosynthetic organisms to adjust to their living environment.