Crystal Structure of Chloroplastic Thioredoxin f2 from Chlamydomonas reinhardtii Reveals Distinct Surface Properties.

Stéphane Lemaire,Daniele Tedesco,Simona Fermani,Pierre Crozet,Julien Henri,Laure Michelet,Mirko Zaffagnini

doi:10.3390/antiox7120171

Abstract

Protein disulfide reduction by thioredoxins (TRXs) controls the conformation of enzyme active sites and their multimeric complex formation. TRXs are small oxidoreductases that are broadly conserved in all living organisms. In photosynthetic eukaryotes, TRXs form a large multigenic family, and they have been classified in different types: f, m, x, y, and z types are chloroplastic, while o and h types are located in mitochondria and cytosol. In the model unicellular alga Chlamydomonas reinhardtii, the TRX family contains seven types, with f- and h-types represented by two isozymes. Type-f TRXs interact specifically with targets in the chloroplast, controlling photosynthetic carbon fixation by the Calvin–Benson cycle. We solved the crystal structures of TRX f2 and TRX h1 from C. reinhardtii. The systematic comparison of their atomic features revealed a specific conserved electropositive crown around the active site of TRX f, complementary to the electronegative surface of their targets. We postulate that this surface provides specificity to each type of TRX.

Highlights

Thioredoxins (TRXs) are small oxidoreductases of 10–16 kDa exhibiting a characteristic three dimensional structure classified as TRX fold [1], composed of a single canonical globular domain comprising a mixed β-sheet surrounded by four α-helices [2,3,4]
Non-photosynthetic organisms contain a limited number of TRXs, which are localized in the Antioxidants 2018, 7, 171; doi:10.3390/antiox7120171
Cytosolic and mitochondrial TRXs are reduced by NTRs, while chloroplastic TRXs are reduced by the iron-sulfur containing ferredoxin–thioredoxin reductase, which derives electrons from ferredoxin and the photosynthetic electron transfer chain [14,15,16,17]

Summary

Introduction

Thioredoxins (TRXs) are small oxidoreductases of 10–16 kDa exhibiting a characteristic three dimensional structure classified as TRX fold [1], composed of a single canonical globular domain comprising a mixed β-sheet surrounded by four α-helices [2,3,4]. These proteins play a key role in controlling the redox status of protein disulfide bonds in all non-parasitic organisms [5]. Cytosolic and mitochondrial TRXs are reduced by NTRs, while chloroplastic TRXs are reduced by the iron-sulfur containing ferredoxin–thioredoxin reductase, which derives electrons from ferredoxin and the photosynthetic electron transfer chain [14,15,16,17]

Methods

Results

Conclusion