New insights on ChlD1 function in Photosystem II from site-directed mutants of D1/T179 in Thermosynechococcus elongatus

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Title: New insights on ChlD1 function in Photosystem II from site-directed mutants of D1/T179 in Thermosynechococcus elongatus
Authors: Takegawa, Y
Nakamura, M
Nakamura, S
Noguchi, T
Sellés, J
Rutherford, AW
Boussac, A
Sugiura, M
Item Type: Journal Article
Abstract: The monomeric chlorophyll, ChlD1, which is located between the PD1PD2 chlorophyll pair and the pheophytin, PheoD1, is the longest wavelength chlorophyll in the heart of Photosystem II and is thought to be the primary electron donor. Its central Mg2+ is liganded to a water molecule that is H-bonded to D1/T179. Here, two site-directed mutants, D1/T179H and D1/T179V, were made in the thermophilic cyanobacterium, Thermosynechococcus elongatus, and characterized by a range of biophysical techniques. The Mn4CaO5 cluster in the water-splitting site is fully active in both mutants. Changes in thermoluminescence indicate that i) radiative recombination occurs via the repopulation of *ChlD1 itself; ii) non-radiative charge recombination reactions appeared to be faster in the T179H-PSII; and iii) the properties of PD1PD2 were unaffected by this mutation, and consequently iv) the immediate precursor state of the radiative excited state is the ChlD1+PheoD1- radical pair. Chlorophyll bleaching due to high intensity illumination correlated with the amount of 1O2 generated. Comparison of the bleaching spectra with the electrochromic shifts attributed to ChlD1 upon QA- formation, indicates that in the T179H-PSII and in the WT*3-PSII, the ChlD1 itself is the chlorophyll that is first damaged by 1O2, whereas in the T179V-PSII a more red chlorophyll is damaged, the identity of which is discussed. Thus, ChlD1 appears to be one of the primary damage site in recombination-mediated photoinhibition. Finally, changes in the absorption of ChlD1 very likely contribute to the well-known electrochromic shifts observed at ~430 nm during the S-state cycle.
Issue Date: 1-Apr-2019
Date of Acceptance: 26-Jan-2019
ISSN: 0005-2728
Publisher: Elsevier
Start Page: 297
End Page: 309
Journal / Book Title: Biochimica et Biophysica Acta - Bioenergetics
Volume: 1860
Issue: 4
Copyright Statement: © 2019 Published by Elsevier B.V. All rights reserved. This manuscript is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International Licence
Sponsor/Funder: The Leverhulme Trust
Biotechnology and Biological Sciences Research Council (BBSRC)
Funder's Grant Number: RPG-2017-223
Keywords: Chl(D1)
Electrochromic shifts
Photosystem II
Reaction center
0601 Biochemistry And Cell Biology
Publication Status: Published
Conference Place: Netherlands
Embargo Date: 2020-01-29
Online Publication Date: 2019-01-29
Appears in Collections:Faculty of Natural Sciences

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