Absorption changes in Photosystem II in the Soret band region upon the formation of the chlorophyll cation radical [P$_{D1}$ P$_{D2}$]$^+$ - Biologie du chloroplaste et perception de la lumière chez les micro-algues Accéder directement au contenu
Pré-Publication, Document De Travail Année : 2022

Absorption changes in Photosystem II in the Soret band region upon the formation of the chlorophyll cation radical [P$_{D1}$ P$_{D2}$]$^+$

Résumé

Flash-induced absorption changes in the Soret region arising from the [P$_{D1}$ P$_{D2}$]$^+$ state, the chlorophyll cation radical formed upon excitation of Photosystem II (PSII), were obtained using Mn-depleted PSII cores at pH 8.6. Under these conditions, Tyr D is reduced before the first flash but oxidised before subsequent flashes. When TyrD$^•$ is present, an additional signal in the [P$_{D1}$ P$_{D2}$]$^+$ -$minus$ -[P$_{D1}$ P$_{D2}$] difference spectrum was observed when compared to the first flash. The additional feature was W-shaped with troughs at 434 nm and 446 nm. This feature was absent when Tyr$_D$ was reduced, but was present when Tyr$_D$ was physically absent (and replaced by phenylalanine) or when its H-bonding histidine (D2-His190) was physically absent (replaced by a Leucine),. Thus, the simple difference spectrum without the double trough feature at 434 nm and 446 nm, required the native structural environment around the reduced Tyr$_D$ and its H bonding partners to be present. A range of PSII variants were surveyed, and we found no evidence of involvement of P$_{D1}$ , Chl$_{D1}$ , Phe$_{D1}$ , Phe$_{D2}$ , TyrZ, and the Cyt$b_{559}$ heme in difference spectrum. Direct data ruling out the participation of P$_{D2}$ is lacking. It seems possible that the specific H-bonding environment of around reduced Tyr$_D$ allows a more homogenous electrostatic environment for [P$_{D1}$$P_{D2}$]$^+$ . A role for P$_{D2}$ in the double-trough Soret signal may be tested using mutants of P$_{D2}$ axial His ligand D2-His197.
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Dates et versions

hal-03795578 , version 1 (04-10-2022)

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Paternité - Pas d'utilisation commerciale - Pas de modification

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Alain Boussac, Miwa Sugiura, Makoto Nakamura, A. William Rutherford, Stefania Viola, et al.. Absorption changes in Photosystem II in the Soret band region upon the formation of the chlorophyll cation radical [P$_{D1}$ P$_{D2}$]$^+$. 2022. ⟨hal-03795578⟩
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