Heteromeric Protein Interactions in Starch Synthesis

Abstract

Starch plays a critical role in the carbon budget of most plants and is one of the most important agricultural commodities in the world. Although the complex, hierarchical structure of the starch granule is largely conserved among plant species, tissue and species-dependent variations in structure exist which relate to different biological functions. A large battery of different classes of enzymes, each with multiple isoforms, is responsible for synthesis of the starch granule. The coordination and cooperation of these enzyme activities is beginning to be understood, and this chapter outlines our current knowledge of the many protein-protein interactions involved in starch granule biosynthesis. Protein-protein interactions are involved in all stages of granule bio-genesis, from precursor formation, granule initiation, and the synthesis of both amylose and amylopectin. Protein phosphorylation plays an important role in regulating some enzyme activities, as well as controlling assembly and disassembly of specific protein complexes. In addition to the core biosynthetic pathway, many auxiliary components, including essential non-catalytic proteins and regulatory protein kinases and phosphatases, are responsible for regulating the coordination of the starch biosynthetic pathway. Current models of granule initiation, and the synthesis of amylose and amylopectin are proposed in relation to current knowledge of the many interacting proteins in this important biochemical pathway.