Modification of the pheophytin redox potential in Therrnosynechococcus elongatus Photosystem II with PsbA3 as D1

In Photosystem II (PSII) of the cyanobacterium Thermosynechococcus elongatus, glutamate 130 in the high-light variant of the D1-subunit (PsbA3) was changed to glutamine in a strain lacking the two other genes for D1, psbA(1) and psbA(2). The resulting PSII (PsbA3/Glu130Gln) was compared with those from the native high-light (PsbA3-PSII) and low-light (PsbA1-PSII) variants, which differ by 21 amino acid including Glu130Gln. H-bonding from D1-Glu130Gln to the primary electron acceptor, Pheophytin(D1) (Pheo(D1)), is known to affect the E-m, of the Pheo(D1)/Pheo((D1) over bar)center dot couple. The Gln130 mutation here had little effect on water splitting, charge accumulation and photosensitivity but did slow down S(2)Q((A) over bar)center dot charge recombination and up-shift the thermoluminescence while increasing its yield. These changes were consistent with a approximate to -30 mV shift of the Pheo(D1)/Pheo((D1) over bar)center dot E-m, similar to earlier single site-mutation results from other species and double the approximate to -17 mV shift seen for PsbA1-PSII versus PsbA3-PSII. This is attributed to the influence of the other 20 amino-acids that differ in PsbA3. A computational model for simulating S(2)Q((A) over bar)center dot recombination matched the experimental trend: the S(2)Q((A) over bar)center dot recombination rate in PsbA1-PSII differed only slightly from that in PsbA3-PSII, while in Glu130-PsbA3-PSII there was a more pronounced slowdown of the radical pair decay. The simulation predicted a major effect of the Pheo(D1)/Pheo((D1) over bar)center dot potential on O-1(2) yield (similar to 60% in PsbA1-PSII, similar to 20% in PsbA3-PSII and similar to 7% in Gln130-PsbA3-PSII), reflecting differential sensitivities to high light. (C) 2013 Elsevier B.V. All rights reserved.