Natively oxidized amino acid residues in the spinach PS I-LHC I supercomplex

Journal Article · 31 December 2019 · Photosynthesis Research

DOI: https://doi.org/10.1007/s11120-019-00698-7 · OSTI ID:1593960

Kale, Ravindra ^[1]; Sallans, Larry ^[2]; Frankel, Laurie K. ^[3]; Bricker, Terry M.  ^[3]

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1. Louisiana State Univ., Baton Rouge, LA (United States); Department of Biological Sciences, Louisiana State University
2. Univ. of Cincinnati, OH (United States)
3. Louisiana State Univ., Baton Rouge, LA (United States)

Reactive oxygen species (ROS) production is an unavoidable byproduct of electron transport under aerobic conditions. Photosystem II (PS II), the cytochrome b₆/ƒ complex and Photosystem I (PS I) are all demonstrated sources of ROS. It has been proposed that PS I produces substantial levels of a variety of ROS including O$$_{2}^{·-}$$, ¹O₂, H₂O₂ and, possibly, ∙OH, however, the site(s) of ROS production within PS I has been the subject of significant debate. We hypothesize that amino acid residues close to the sites of ROS generation will be more susceptible to oxidative modification than distant residues. In this study, we have identified oxidized amino acid residues in spinach PS I which was isolated from field-grown spinach. The modified residues were identified by high-resolution tandem mass spectrometry. As expected, many of the modified residues lie on the surface of the complex. However, a well-defined group of oxidized residues, both buried and surface-exposed, lead from the chl a’ of P₇₀₀ to the surface of PS I. These residues (PsaB: ⁶⁰⁹F, ⁶¹¹E, ⁶¹⁷M, ⁶¹⁹W, ⁶²⁰L, and PsaF: ¹³⁹L, ¹⁴²A,¹⁴³D) may identify a preferred route for ROS, probably ¹O₂, to egress the complex from the vicinity of P₇₀₀. Additionally, two buried residues located in close proximity to A1B (PsaB:⁷¹²H and ⁷¹⁴S) were modified, which may be consistent with A_1B being a source of O$$_{2}^{·-}$$. Surprisingly, no oxidatively modified residues were identified in close proximity to the 4Fe-FS clusters F_X, F_A or F_B. These cofactors had been identified as a principal targets for ROS damage in the photosystem. Finally, a large number of residues located in the hydrophobic cores of Lhca1-Lhca4 are oxidatively modified. These appear to be the result of ¹O₂ production by the distal antennae for the photosystem.

• Research Organization: Louisiana State Univ., Baton Rouge, LA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division
• Grant/Contract Number: FG02-98ER20310
• OSTI ID: 1593960
• Journal Information: Photosynthesis Research, Journal Name: Photosynthesis Research Journal Issue: 3 Vol. 143; ISSN 0166-8595
• Publisher: SpringerCopyright Statement
• Country of Publication: United States
• Language: English