Thiol-based redox control of enzymes involved in the tetrapyrrole biosynthesis pathway in plants

Andreas S Richter,Bernhard Grimm

doi:10.3389/fpls.2013.00371

Abstract

The last decades of research brought substantial insights into tetrapyrrole biosynthetic pathway in photosynthetic organisms. Almost all genes have been identified and roles of seemingly all essential proteins, leading to the synthesis of heme, siroheme, phytochromobilin, and chlorophyll (Chl), have been characterized. Detailed studies revealed the existence of a complex network of transcriptional and post-translational control mechanisms for maintaining a well-adjusted tetrapyrrole biosynthesis during plant development and adequate responses to environmental changes. Among others one of the known post-translational modifications is regulation of enzyme activities by redox modulators. Thioredoxins and NADPH-dependent thioredoxin reductase C (NTRC) adjust the activity of tetrapyrrole synthesis to the redox status of plastids. Excessive excitation energy of Chls in both photosystems and accumulation of light-absorbing unbound tetrapyrrole intermediates generate reactive oxygen species, which interfere with the plastid redox poise. Recent reports highlight ferredoxin-thioredoxin and NTRC-dependent control of key steps in tetrapyrrole biosynthesis in plants. In this review we introduce the regulatory impact of these reductants on the stability and activity of enzymes involved in 5-aminolevulinic acid synthesis as well as in the Mg-branch of the tetrapyrrole biosynthetic pathway and we propose molecular mechanisms behind this redox control.

Highlights

Regulation of the redox status of processes taking place in plastids, including the tetrapyrrole metabolism, by disulfide bond formation and reduction is one of the crucial post-translational control mechanisms to modulate protein activity, folding, and stability
In this review we introduce the regulatory impact of these reductants on the stability and activity of enzymes involved in 5-aminolevulinic acid synthesis as well as in the Mg-branch of the tetrapyrrole biosynthetic pathway and we propose molecular mechanisms behind this redox control
The thiol-reducing systems that control the redox state of enzymes of tetrapyrrole will be introduced in Section “Thiol-Based Redox Regulators of Higher Plants,” while the significant role of posttranslational redox control in tetrapyrrole biosynthesis will be discussed in Section “The Need for Post-Translational Redox Regulation in Tetrapyrrole Biosynthesis.”

Summary

Introduction

INTRODUCTION Regulation of the redox status of processes taking place in plastids, including the tetrapyrrole metabolism, by disulfide bond formation and reduction is one of the crucial post-translational control mechanisms to modulate protein activity, folding, and stability. Western blot analysis of the tetrapyrrole biosynthesis enzymatic proteins in a ntrc mutant of A. thaliana revealed reduced content of GluTR, POR, and CHLM (Richter et al, 2013; see Redox Modifications of ALA Synthesis Enzymes and Redox Control in the Mg-Branch).

Results

Conclusion