Amino acid oxidation of the D1 and D2 proteins by oxygen radicals during photoinhibition of Photosystem II
Friday, 2017/03/17 | 07:54:45
|
Ravindra Kale, Annette E. Hebert, Laurie K. Frankel, Larry Sallans, Terry M. Bricker, and Pavel Pospíšil SignificanceReactive oxygen species (ROS) damage the D1 and D2 reaction center proteins of Photosystem II in a process known as photoinhibition. Photoinhibition is an unavoidable consequence of excitation energy transfer and electron transport. The ROS responsible for oxidative damage, the sites of ROS production, and the residues oxidatively modified have not been determined. In this work, we identify HO• as being produced on both the oxidizing and reducing sides of the photosystem. O2•− also appears to be produced at either PheoD1 or QA. Additionally, residues on the D1 and D2 proteins were identified that are oxidatively modified during a photoinhibitory timecourse. Finally, we propose plausible pathways for the propagation of protein oxidation events in the D1 and D2 proteins. AbstractThe Photosystem II reaction center is vulnerable to photoinhibition. The D1 and D2 proteins, lying at the core of the photosystem, are susceptible to oxidative modification by reactive oxygen species that are formed by the photosystem during illumination. Using spin probes and EPR spectroscopy, we have determined that both O2•− and HO• are involved in the photoinhibitory process. Using tandem mass spectroscopy, we have identified a number of oxidatively modified D1 and D2 residues. Our analysis indicates that these oxidative modifications are associated with formation of HO• at both the Mn4O5Ca cluster and the nonheme iron. Additionally, O2•− appears to be formed by the reduction of O2 at either PheoD1 or QA. Early oxidation of D1:332H, which is coordinated with the Mn1 of the Mn4O5Ca cluster, appears to initiate a cascade of oxidative events that lead to the oxidative modification of numerous residues in the C termini of the D1 and D2 proteins on the donor side of the photosystem. Oxidation of D2:244Y, which is a bicarbonate ligand for the nonheme iron, induces the propagation of oxidative reactions in residues of the D-de loop of the D2 protein on the electron acceptor side of the photosystem. Finally, D1:130E and D2:246M are oxidatively modified by O2•− formed by the reduction of O2 either by PheoD1•− or QA•−. The identification of specific amino acid residues oxidized by reactive oxygen species provides insights into the mechanism of damage to the D1 and D2 proteins under light stress.
See: http://www.pnas.org/content/114/11/2988.abstract.html?etoc PNAS March 14 2017; vol.114; no.11: 2988–2993
Fig. 1. Timecourse for photoinactivation. PSII membranes (100 μg of Chl⋅mL−1) were incubated in the dark (squares) or illuminated with high intensity red light either in the absence (circles) or presence (triangles) of 0.4 mM DCBQ + 1 mM FeCN. At various time points, samples were removed and assayed for O2 evolution capacity. Control O2 evolution rates were 400–500 μmol O2⋅mg−1 Chl⋅h−1. Each point represents the mean value and the SD of three experiments (mean ± SD, n = 3).
|
Back Print View: 380 |
[ Other News ]___________________________________________________
|