Unraveling the Activation Mechanism of the Potato Tuber ADP-Glucose Pyrophosphorylase

Abstract

ADP-glucose pyrophosphorylase regulates the synthesis of glycogen in bacteria and of starch in plants. The enzyme from plants is mainly activated by 3-phosphoglycerate and is a heterotetramer comprising two small and two large subunits. Here, we found that two highly conserved residues are critical for triggering the activation of the potato tuber ADP-glucose pyrophosphorylase, as shown by site-directed mutagenesis. Mutations in the small subunit, which bears the catalytic function in this potato tuber form, had a more dramatic effect on disrupting the allosteric activation than those introduced in the large subunit, which is mainly modulatory. Our results strongly agree with a model where the modified residues are located in loops responsible for triggering the allosteric activation signal for this enzyme, and the sensitivity to this activation correlates with the dynamics of these loops. In addition, previous biochemical data indicates that the triggering mechanism is widespread in the enzyme family, even though the activator and the quaternary structure are not conserved.

Structural analysis reveals a pyruvate-binding activator site in the Agrobacterium tumefaciens ADP–glucose pyrophosphorylase

“…As part of the identified heterogeneity among 20 monomers in one asymmetric unit, we were able to resolve, in some subunits, parts of the loop 96 -108. This loop has been implicated in regulation in both E. coli and potato tuber homologues (18,19). We identified that residues 96 and 97 (N-end of this loop) deviate nearly 180°from the direction previously reported.…”

Fruit-localized phytochromes regulate plastid biogenesis, starch synthesis, and carotenoid metabolism in tomato

“…S6 ). Catalysing the first committed step in starch biosynthesis, ADP-glucose pyrophosphorylase (AGPase) is a heterotetramer comprising a pair of small/catalytic and a pair of large/regulatory subunits ( Kim et al , 2007 ; Figueroa et al , 2013 ). Among the tomato genes encoding the large AGPase subunits, both SlAGPaseL1 and SlAGPaseL3 were up-regulated whereas SlAGPaseL2 mRNA levels remained unchanged in immature fruits of SlPHYA RNAi plants.…”

ADP‐glucose pyrophosphorylase genes, associated with kernel weight, underwent selection during wheat domestication and breeding

“…The LSUs mainly have regulatory roles and the SSUs have catalytic roles, and recent studies indicate that LSUs also contribute substrate binding (Cakir et al ., ; Hwang et al ., ; Kavakli et al ., ). AGPases are activated by 3‐phosphoglyceric acid and inhibited by inorganic phosphate (Boehlein et al ., ; Figueroa et al ., ; Heldt et al ., ; Neuhaus et al ., ). In nonphotosynthetic cells, AGPases have different localizations in dicots and monocots (Comparot‐Moss and Denyer, ).…”