Ultrafast exciton dynamics energy transfer in the Cryptophyte Light-Harvesting Antenna phycoerythrin 566

Na Guo¹Zidong Liang²Xinyu Guo²Zhencheng Huang²Wenjun Li³Mingyuan Xie^2*Yang PU⁴Min Chen⁵Song Qin³Fuli ZHAO^2*

• ¹School of Business Administration, Tongling, China
• ²Sun Yat-Sen University, Guangzhou, China
• ³Chinese Academy of Sciences Yantai Institute of Coastal Zone Research, Yantai, China
• ⁴Ludong University, Yantai, China
• ⁵Yantai University, Yantai, China

Abstract :Cryptophytes obtain energy through photosynthetic pigments and transfer it to the photosynthetic center in the ultrafast time scale. The mechanisms of such ultrafast excitation energy transfer (EET) in light-trapping complexes are a major focus of algal research. The closed form phycoerythrin 566 (PE566) bind chemically distinct chromophores, exhibiting different spectral properties with the other closed form phycobiliproteins of Cryptophytes. To the elucidation of the ultrafast energy transfer pathway of PE566 may lead to the deep understanding of the mechanisms of the initial process of photosynthesis. We present a fine global description of the ultrafast energy transfer kinetics of PE566 under physiological setting. We employed a method combining ultrafast transient absorption spectroscopy (TA) and coherent modified Redfield theory (CMRT) for theoretical modeling to demonstrate the ultrafast energy transfer between pigment molecules including the exciton dynamics in PE566. The results indicate that in the PE566 dimer, the two phycoerythrobilins (PEBs) possess the highest excitation energies and serve as the primary donors of the EET process. The two double-linked bilin584s, serving as the secondary energy transfer acceptor which exhibiting strong electronic coupling and leading to coherent delocalization of excited states. Two single-linked bilin584s and two bilin618s constitute the four lowest energy exciton states. Ultimately, two efficient EET pathways are identified, with the lowest energy bilin618s serving as an energy transfer terminal in PE566. Our work clarifies the internal EET mechanism of Cryptoptyta PE566, which may enrich the photophysical studies of phycobiliprotein systems.