Tocopherol controls D1 amino acid oxidation by oxygen radicals in Photosystem II

Photosystem II (PSII) is an intrinsic membrane protein complex that functions as a light-driven water:plastoquinone oxidoreductase in oxygenic photosynthesis. Electron transport in PSII is associated with formation of reactive oxygen species (ROS) responsible for oxidative modifications of PSII proteins. In this study, oxidative modifications of the D1 and D2 proteins by the superoxide anion (O-2(center dot-)) and the hydroxyl (HO center dot) radicals were studied in WT and a tocopherol cyclase (vtel) mutant, which is deficient in the lipid-soluble antioxidant alpha-tocopherol. In the absence of this antioxidant, high-resolution tandem mass spectrometry was used to identify oxidation of D1:E-130 to hydroxyglutamic acid by O-2(center dot- ) at the Pheopi site. Additionally, D1:Y-246 was modified to either tyrosine hydroperoxide or dihydroxyphenylalanine by O(2)(center dot- )and HO center dot, respectively, in the vicinity of the nonheme iron. We propose that a-tocopherol is localized near Pheopi and the nonheme iron, with its chromanol head exposed to the lipid-water interface. This helps to prevent oxidative modification of the amino acid's hydrogen that is bonded to Pheopi and the nonheme iron (via bicarbonate), and thus protects electron transport in PSII from ROS damage.

Automated summary

This study investigates the oxidative modifications of D1 and D2 proteins in PSII by superoxide anion and hydroxyl radicals, revealing that the presence of alpha-tocopherol helps prevent oxidative damage to PSII.