S80: Structural evolution of regulatory connections between primary and specialized metabolism in plants: the example of APS kinase and glucosinolates

Coordination of primary and specialized metabolism requires control of key enzymes at different points in biochemical systems. In eukaryotes and prokaryotes, adenosine-5’-phosphosulfate (APS) kinase (APSK) catalyzes the phosphorylation of APS to 3’-phosphoadenosine-5’-phosphosulfate (PAPS), which is used in the sulfonation of an array of small molecules. In plants, APSK is essential for reproductive viability and competes with APS reductase to partition sulfate between the primary and secondary branches of the sulfur assimilatory pathway; however, the biochemical regulation of APSK is poorly understood. Crystallographic studies of Arabidopsis APSK reveal how cellular redox-state controls this enzyme at a critical connection between primary and specialized (i.e., glucosinolate) metabolism. Structural, functional, and sequence analyses suggests that redox-sensitive APSK evolved after bifurcation of the sulfur assimilatory pathway in the green plant lineage and that changes in redox environment resulting from oxidative stresses may affect partitioning of APS into the primary and secondary thiol metabolic routes by having opposing effects on APSK and APS reductase in plants.