Structure, function, and evolution of plant ADP-glucose pyrophosphorylase

KEY MESSAGE: This review outlines research performed in the last two decades on the structural, kinetic, regulatory and evolutionary aspects of ADP-glucose pyrophosphorylase, the regulatory enzyme for starch biosynthesis. ADP-glucose pyrophosphorylase (ADP-Glc PPase) catalyzes the first committed step in the pathway of glycogen and starch synthesis in bacteria and plants, respectively. Plant ADP-Glc PPase is a heterotetramer allosterically regulated by metabolites and post-translational modifications. In this review, we focus on the three-dimensional structure of the plant enzyme, the amino acids that bind the regulatory molecules, and the regions involved in transmitting the allosteric signal to the catalytic site. We provide a model for the evolution of the small and large subunits, which produce heterotetramers with distinct catalytic and regulatory properties. Additionally, we review the various post-translational modifications observed in ADP-Glc PPases from different species and tissues. Finally, we discuss the subcellular localization of the enzyme found in grain endosperm from grasses, such as maize and rice. Overall, this work brings together research performed in the last two decades to better understand the multiple mechanisms involved in the regulation of ADP-Glc PPase. The rational modification of this enzyme could improve the yield and resilience of economically important crops, which is particularly important in the current scenario of climate change and food shortage.