Structure of mammalian AMPK and its regulation by ADP

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Abstract

The heterotrimeric AMP-activated protein kinase (AMPK) has a key role in regulating cellular energy metabolism; in response to a fall in intracellular ATP levels it activates energy-producing pathways and inhibits energy-consuming processes1. AMPK has been implicated in a number of diseases related to energy metabolism including type 2 diabetes, obesity and, most recently, cancer2,3,4,5,6. AMPK is converted from an inactive form to a catalytically competent form by phosphorylation of the activation loop within the kinase domain7: AMP binding to the γ-regulatory domain promotes phosphorylation by the upstream kinase8, protects the enzyme against dephosphorylation, as well as causing allosteric activation9. Here we show that ADP binding to just one of the two exchangeable AXP (AMP/ADP/ATP) binding sites on the regulatory domain protects the enzyme from dephosphorylation, although it does not lead to allosteric activation. Our studies show that active mammalian AMPK displays significantly tighter binding to ADP than to Mg-ATP, explaining how the enzyme is regulated under physiological conditions where the concentration of Mg-ATP is higher than that of ADP and much higher than that of AMP. We have determined the crystal structure of an active AMPK complex. The structure shows how the activation loop of the kinase domain is stabilized by the regulatory domain and how the kinase linker region interacts with the regulatory nucleotide-binding site that mediates protection against dephosphorylation. From our biochemical and structural data we develop a model for how the energy status of a cell regulates AMPK activity.

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Figure 1: Role of ADP in regulation of AMPK activity.
Figure 2: Measurement of equilibrium dissociation constants for the binding of AXPs to phosphorylated AMPK.
Figure 3: Crystal structure of active mammalian AMPK.
Figure 4: Mutational analysis of AMPK regulation.

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Protein Data Bank

Data deposits

Coordinates and structure factors have been deposited in the Protein Data Bank with accession codes 2Y8L, 2Y8Q, 2Y94 and 2YA3.

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Acknowledgements

We thank M. Webb for gift of coumarin nucleotides, J. Skehel for comments on the manuscript and S. Smerdon for discussion and assistance. Work in both laboratories is supported by the MRC and we gratefully acknowledge Diamond Light Source for synchrotron access.

Author information

B.X., M.J.S., E.U., R.H., F.V.M., D. Carmena, C.J., P.A.W., J.F.E., L.F.H., P.S., S.A.H., R.A. and S.R.M. performed experiments. All authors contributed to data analysis, experimental design and manuscript writing.

Correspondence to David Carling or Steven J. Gamblin.

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The authors declare no competing financial interests.

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The file contains Supplementary Figures 1-12 with legends, Supplementary Tables 1-3 and Supplementary Methods which include 3 additional figures with legends. (PDF 2537 kb)

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Xiao, B., Sanders, M., Underwood, E. et al. Structure of mammalian AMPK and its regulation by ADP. Nature 472, 230–233 (2011) doi:10.1038/nature09932

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