X-ray crystallographic and high-speed AFM studies of peroxiredoxin 1 fromChlamydomonas reinhardtii

Abstract

Peroxiredoxins (PRXs) are a group of antioxidant enzymes that are found in all organisms, including plants and green algae. The 2-Cys PRX fromChlamydomonas 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 onCrPRX1, especially regarding its oligomeric state. In this study, high-speed atomic force microscopy (HS-AFM) images ofCrPRX1 and an X-ray crystallographic analysis have enabled examination of the oligomeric state ofCrPRX1. Diffraction data from a crystal of the Cys174Ser mutant ofCrPRX1 indicate the existence of noncrystallographic fivefold symmetry. HS-AFM images ofCrPRX1 further show thatCrPRX1 particles form rings with pentagonal rotational symmetry. On the basis of these findings, the oligomeric state ofCrPRX1 is discussed and it is concluded that this PRX exists in a ring-shaped decameric form comprising a pentamer of dimers.