Frequency-Domain Spectroscopic Study of the Photosystem I Supercomplexes, Isolated IsiA Monomers, and the Intact IsiA Ring

• DOI: 10.1021/acs.jpcb.2c04829
• Publication Date: 2022-09-06T03:39:17Z
• Authors: Tonu Reinot; Anton Khmelnitskiy; Valter Zazubovich; Hila Toporik; Yuval Mazor; Ryszard Jankowiak
• Keywords: Trimer; P700

The PSI3–IsiA18 supercomplex is one of the largest and most complicated assemblies in photosynthesis. IsiA ring, composed 18 monomers (IsiA18) surrounding PSI trimer (PSI3), forms under iron-deficient conditions cyanobacteria acts as a peripheral antenna. Based on structure recently determined via cryo-EM imaging, we model various optical spectra IsiA18 ring. Comparison absorption emission isolated full ring reveals that about 2.7 chlorophylls (Chls) are lost monomers. best fits for obtained assuming absence Chl 508 517 70% loss 511. describing all three hexamers entire suggests lowest energy pigments Chls 511, 514, 517. modeling results presented this work, conclude there likely entry points EET from IsiA6 hexamer to core monomer, with two these being located next each other (i.e., nine PSI3 trimer). Finally, show excitation transfer inside individual fast (<2 ps at T = 5 K) least 20 times faster than intermonomer transfer.