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

Abstract

Reactive oxygen species (ROS) production is an unavoidable byproduct of electron transport under aerobic conditions. Photosystem II (PS II), the cytochrome b6f 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 O2∙ ^-, ¹O ₂, H ₂O ₂ 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 P ₇₀₀ 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 ¹O ₂, to egress the complex from the vicinity of Pmore » ₇₀₀. 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 ¹O ₂ production by the distal antennae for the photosystem.« less

Authors:

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

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+ Show Author Affiliations

1. Louisiana State Univ., Baton Rouge, LA (United States)
2. Univ. of Cincinnati, OH (United States)

Publication Date:

2020-01-01

Research Org.:

Louisiana State Univ., Baton Rouge, LA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division

OSTI Identifier:

1593960

Grant/Contract Number:  

FG02-98ER20310

Resource Type:

Accepted Manuscript

Journal Name:

Photosynthesis Research

Additional Journal Information:

Journal Name: Photosynthesis Research; Journal ID: ISSN 0166-8595

Publisher:

Springer

Country of Publication:

United States

Language:

English

Subject:

59 BASIC BIOLOGICAL SCIENCES; Photosystem I; tandem mass spectrometry; Reactive Oxygen Species (ROS); spinach