Mechanisms and Functions of Post-translational Enzyme Modifications in the Organization and Control of Plant Respiratory Metabolism

The respiratory pathways of glycolysis, the tricarboxylic acid (TCA) cycle, and mitochondrial electron transport chain are central features of carbon metabolism and bioenergetics in eukaryotic cells. As respiration forms the core of intermediary metabolism, it plays a pivotal role in the growth and metabolism of all photosynthetic organisms. The aim of this chapter is to provide an overview of the occurrence and functions of enzyme post-translational modifications (PTMs) in the control of plant respiration including sucrose catabolism. PTMs are covalent alterations of amino acid residues within a particular polypeptide. Diverse PTMs represent pivotal regulatory events that integrate signaling, gene expression, and metabolism with developmental and stress responses in eukaryotic cells. These PTMs are often rapid and reversible and can not only dramatically alter enzyme activity, but may also generate specific PTM-dependent docking sites that influence interactions with other proteins. In yeast, enzyme PTMs exert more control over glycolysis and mitochondrial metabolism than do changes in transcripts or enzyme abundance, and the same situation likely applies to vascular plants. Recent advances in proteomics, particularly the development of novel and specific chemistries along with affiliated mass spectrometry techniques for detection and mapping of diverse PTMs, are rapidly expanding the catalogue of respiratory enzymes whose functions may be controlled by reversible covalent modification. Phosphorylation-dephosphorylation and disulfide-dithiol interconversion appear to be the most prevalent types of reversible covalent modification used in plant enzyme control. Additional PTMs such as monoubiquitination, S-nitrosylation, and acetylation also appear to play important roles. However, the biochemical impact of in vivo PTMs on the functional properties of plant respiratory enzymes remains mostly unknown and thus remains an important goal for future research. Rational manipulation of PTM events is expected to make an important contribution to the implementation of effective biotechnological strategies for engineering grain crops for increased yields via metabolic engineering.