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Locating the Missing Chlorophylls f in Far-red Photosystem I

Consoli, G.; Tufail, F.; Leong, H. F.; Viola, S.; Davis, G. A.; Medranda, D.; Rew, N.; Hofer, M.; Simpson, P.; Sandrin, M.; Chachuat, B.; Nelson, J.; Renger, T.; Murray, J. W.; Fantuzzi, A.; Rutherford, A. W.

2024-08-06 biochemistry
10.1101/2024.08.06.606606 bioRxiv
Show abstract

The discovery of chlorophyll f-containing oxygenic photosynthesis, with its long-wavelength photochemistry, represented a new low-energy paradigm. However, subsequent structural studies on chlorophyll f-containing Photosystem I (PSI) found five chlorophylls f but none among the photochemically active pigments and concluded that chlorophyll f plays no photochemical role. Here we report a cryo-EM structure (2.01 [A]) of far-red PSI from Chroococcidiopsis thermalis PCC 7203, showing all eight chlorophylls f, including the redox active A-1B. Simulations of absorption difference spectra induced by charge separation indicate that the A-1B chlorophyll f absorbs at 755 nm. The chlorophyll f sites, some wavelength assignments, and conserved far-red-specific amino acids, provide functional insights, including redox tuning of chlorophyll f as the primary donor and far-red excitation energy-sharing over the PSI trimer.

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