Cationic state distribution over the chlorophyll d-containing PD1/PD2 pair in photosystem II

Most of the chlorophyll (Chl) cofactors in photosystem II (PSII) from Acaryochloris marina are Chld, although a few Chla molecules are also present. To evaluate the possibility that Chla may participate in the PD1/PD2 Chl pair in PSII from A. marina, the PD1
• +/PD2
• + charge ratio was investigated using the PSII crystal structure analyzed at 1.9-Å resolution, while considering all possibilities for the Chld-containing PD1/PD2 pair, i.e., Chld/Chld, Chla/Chld, and Chld/Chla pairs. Chld/Chld and Chla/Chld pairs resulted in a large PD1
• + population relative to PD2
• +, as identified in Chla/Chla homodimer pairs in PSII from other species, e.g., Thermosynechococcus elongatus PSII. However, the Chld/Chla pair possessed a PD1
• +/PD2
• + ratio of approximately 50/50, which is in contrast to previous spectroscopic studies on A. marina PSII. The present results strongly exclude the possibility that the Chld/Chla pair serves as PD1/PD2 in A. marina PSII. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.

► The PD1
• +/PD2
• + charge ratio was investigated for the Chld-containing PD1/PD2 pair.
► Chld/Chld and Chla/Chld pairs resulted in a large PD1
• + population relative to PD2
• +.
► However, the Chld/Chla pair possessed a PD1
• +/PD2
• + ratio of approximately 50/50.
► The present results strongly exclude the possibility that the Chld/Chla pair serves as PD1/PD2 in Acaryochloris marina PSII.