Post-Translational Modifications of the Energy Guardian AMP-Activated Protein Kinase

Abstract

Physical exercise elicits physiological metabolic perturbations such as energetic and oxidative stress; however, a diverse range of cellular processes are stimulated in response to combat these challenges and maintain cellular energy homeostasis. AMP-activated protein kinase (AMPK) is a highly conserved enzyme that acts as a metabolic fuel sensor and is central to this adaptive response to exercise. The complexity of AMPK’s role in modulating a range of cellular signalling cascades is well documented, yet aside from its well-characterised regulation by activation loop phosphorylation, AMPK is further subject to a multitude of additional regulatory stimuli. Therefore, in this review we comprehensively outline current knowledge around the post-translational modifications of AMPK, including novel phosphorylation sites, as well as underappreciated roles for ubiquitination, sumoylation, acetylation, methylation and oxidation. We provide insight into the physiological ramifications of these AMPK modifications, which not only affect its activity, but also subcellular localisation, nutrient interactions and protein stability. Lastly, we highlight the current knowledge gaps in this area of AMPK research and provide perspectives on how the field can apply greater rigour to the characterisation of novel AMPK regulatory modifications.

Lessons from Comparison of Hypoxia Signaling in Plants and Mammals

“…In mammals, AMPK is also regulated via ubiquitination and proteasomal degradation through mechanisms that involve several E3 ubiquitin ligases and ubiquitin chains (e.g., K29, K63, and K48 [ 127 , 128 , 129 , 130 ]), depending on the organ or tissue, or physiological conditions. For a more comprehensive review on this topic, we refer the reader to [ 131 ]. Here, we will instead focus on selected examples that illustrate the opposite roles played by the ubiquitin/proteasome system in the regulation of AMPK.…”

“…In mammals, AMPK is also regulated via ubiquitination and proteasomal degradation through mechanisms that involve several E3 ubiquitin ligases and ubiquitin chains (e.g., K29, K63, and K48 [127][128][129][130]), depending on the organ or tissue, or physiological conditions. For a more comprehensive review on this topic, we refer the reader to [131].…”

Investigation of the specificity and mechanism of action of the ULK1/AMPK inhibitor SBI-0206965

“…In addition, the binding of AMP, but not ADP, further increases AMPK activity through allosteric stimulation [ 13 ]. AMPK activity is, therefore, regulated in a multi-layered process, often involving a combination of posttranslational modifications and allosteric regulation [ 16 ].…”

Novel torin1-sensitive phosphorylation sites on the metabolic regulator AMPK revealed by label-free mass spectrometry

“…The a-subunit kinase domain (a-KD) possesses an archetypal kinase domain structure with an activation loop phosphorylation site a1 T174 /a2 T172 (a T172 ) targeted by liver kinase B1 (LKB1) and calcium/calmodulin-dependent kinase kinase 2 (CaMKK2) [8][9][10][11]. Additional COOHterminal regulatory elements on the a-subunit include a tri-helical autoinhibitory domain (AID), a-regulatory subunit-interacting motifs (a-RIM) that interact with the g-subunit, and a serine/threonine-rich loop (ST loop) heavily modified by phosphorylation [12]. The b-subunit is capable of anchoring to carbohydrates through its carbohydrate binding module (CBM), and it contains a COOH-terminal a-g-subunit binding sequence critical for complex formation [13].…”

“…However, p-a T172 is not absolutely required for AMPK activity in vitro and in cellulo, where significant synergist allosteric activation of up to 1000-fold can be achieved with dephosphorylated a T172 via dual ligand binding of an ADaM site compound with AMP [20]. Given AMPK's central role in regulating metabolism, it is unsurprising that it is also subject to multidirectional regulatory inputs via a range of phosphorylation sites present across each of its subunits [12]. mTOR is the catalytic component of mTORC1 and mTORC2, two structurally and functionally distinct multi-protein complexes defined by unique regulatory partners (mTORC1, Raptor; mTORC2, Rictor/SIN1) that dictate substrate selectivity.…”