Interaction of the GntR-family transcription factor Sll1961 with thioredoxin in the cyanobacterium Synechocystis sp. PCC 6803

Junichi Kujirai,Yoshiki Oka,Taro Kadowaki,Yukako Hihara,Yuuki Hayashi,Munehito Arai,Sato Nanba,Yoshitaka Nishiyama

doi:10.1038/s41598-018-25077-5

Abstract

Changes in the redox state of the photosynthetic electron transport chain act as a signal to trigger acclimation responses to environmental cues and thioredoxin has been suggested to work as a key factor connecting the redox change with transcriptional regulation in the cyanobacterium Synechocystis sp. PCC 6803. We screened for redox-dependent transcription factors interacting with thioredoxin M (TrxM) and isolated the GntR-type transcription factor Sll1961 previously reported to be involved in acclimation responses of the photosynthetic machinery. Biochemical analyses using recombinant Sll1961 proteins of wild type and mutants of three cysteine residues, C124, C229 and C307, revealed that an intramolecular disulfide bond is formed between C229 and C307 under oxidizing conditions and TrxM can reduce it by attacking C307. Sll1961 exists in a dimeric form of about 80 kDa both under reducing and oxidizing conditions. C124 can form an intermolecular disulfide bond but it is not essential for dimerization. Based on these observations, tertiary structure models of the Sll1961 homodimer and the Sll1961-TrxM complex were constructed.

Highlights

Photosynthetic organisms perceive changes in environmental cues as the redox changes of the electron transfer components located in the photosynthetic electron transport chain and start acclimation responses to balance the photosynthetic energy supply and its consumption by various metabolic reactions[1,2]
Interaction between Sll1961 and thioredoxin M (TrxM) detected in E. coli co-expression strain
A Histagged Sll1961 (His-Sll1961) and S-tagged TrxMC35S are co-expressed in E. coli Origami[2] (DE3) cells carrying mutations in glutathione reductase and thioredoxin reductase genes to facilitate disulfide bonds formation in the cytoplasm

Summary

Introduction

Photosynthetic organisms perceive changes in environmental cues as the redox changes of the electron transfer components located in the photosynthetic electron transport chain and start acclimation responses to balance the photosynthetic energy supply and its consumption by various metabolic reactions[1,2]. As the acclimation responses take place to mitigate the over-reduction of the photosynthetic electron transport chain, PedR returns to the active form again. This mechanism seems to enable transient induction or repression of the target genes in response to sudden changes in photon flux density. Biochemical analyses using recombinant Sll1961 proteins of wild-type (WT) and mutants of three cysteine residues revealed that TrxM can reduce the intramolecular disulfide bond between C229 and C307 in Sll1961. Based on these experimental results, the structure model of the Sll1961-TrxM complex was constructed

Methods

Results

Conclusion