Abstract
Peroxiredoxins (PRXs) are a group of antioxidant enzymes that are found in all organisms, including plants and green algae. The 2-Cys PRX from Chlamydomonas reinhardtii (CrPRX1) is a chloroplast-localized protein that is critical for clearing reactive oxygen species in chloroplasts. CrPRX1 is reduced by thioredoxins or calredoxin (CrCRX), a recently identified calcium-dependent redox protein. The molecular interaction between PRXs and thioredoxin/CrCRX is functionally important, but discussion has been limited owing to a lack of structural information on CrPRX1, especially regarding its oligomeric state. In this study, high-speed atomic force microscopy (HS-AFM) images of CrPRX1 and an X-ray crystallographic analysis have enabled examination of the oligomeric state of CrPRX1. Diffraction data from a crystal of the Cys174Ser mutant of CrPRX1 indicate the existence of noncrystallographic fivefold symmetry. HS-AFM images of CrPRX1 further show that CrPRX1 particles form rings with pentagonal rotational symmetry. On the basis of these findings, the oligomeric state of CrPRX1 is discussed and it is concluded that this PRX exists in a ring-shaped decameric form comprising a pentamer of dimers.
Highlights
Photosynthesis is a light-dependent chemical process that converts light energy to chemical energy
Light energy is absorbed by chlorophylls or carotenoids in antenna proteins, and is transferred to photosystem complexes, either photosystem II or I, which perform charge separation at the core of the complex
High-intensity light may lead to the production of reactive oxygen species (ROS) such as singlet oxygen (1O2), superoxide (OÀ2 ), hydroxyl radicals (HO ) or hydrogen peroxide (H2O2)
Summary
Photosynthesis is a light-dependent chemical process that converts light energy to chemical energy. High-intensity light may lead to the production of reactive oxygen species (ROS) such as singlet oxygen (1O2), superoxide (OÀ2 ), hydroxyl radicals (HO ) or hydrogen peroxide (H2O2). These ROS are harmful to photosystems and other chloroplast proteins, and may induce photoinhibition (Takahashi & Badger, 2011). Plants and other organisms have developed several mechanisms to avoid light-induced photoinhibition, such as ROS-scavenging systems (Asada, 2006), phototaxis in green alga (Erickson et al, 2015) and nonphotochemical quenching, which converts the excess light into thermal energy that can be dissipated
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