How to catch a dynamic state
AMP-activated protein kinase (AMPK) is a key sensor of energy status in eukaryotes. Its dynamic structure is regulated by allosteric factors including phosphorylation and binding of nucleotides and metabolites. Yan et al. developed conformation-specific antibodies that trap AMPK in a fully inactive state that has experienced a large, domain-level rotation. Biophysical experiments in cells and in vitro are consistent with the structural work and support a model in which the activation loop is fully exposed in the completely inactive, dephosphorylated state. These structures inform our understanding of the complex allosteric behavior in this crucial metabolic regulator.
Science, abe7565, this issue p. 413
Abstract
Adenosine monophosphate (AMP)тАУactivated protein kinase (AMPK) regulates metabolism in response to the cellular energy states. Under energy stress, AMP stabilizes the active AMPK conformation, in which the kinase activation loop (AL) is protected from protein phosphatases, thus keeping the AL in its active, phosphorylated state. At low AMP:ATP (adenosine triphosphate) ratios, ATP inhibits AMPK by increasing AL dynamics and accessibility. We developed conformation-specific antibodies to trap ATP-bound AMPK in a fully inactive, dynamic state and determined its structure at 3.5-angstrom resolution using cryoтАУelectron microscopy. A 180┬░ rotation and 100-angstrom displacement of the kinase domain fully exposes the AL. On the basis of the structure and supporting biophysical data, we propose a multistep mechanism explaining how adenine nucleotides and pharmacological agonists modulate AMPK activity by altering AL phosphorylation and accessibility.
