Understanding the mechanism of direct activation of AMP-kinase: Towards a fine allosteric tuning of the kinase activity.

Mammalian AMP-activated protein kinase (AMPK) is a Ser/Thr protein kinase with a key role as a sensor in cellular energy homeostasis. It has a major role in numerous metabolic disorders, such as type 2 diabetes, obesity, and cancer, and hence it has gained progressive interest as a potential therapeutic target. AMPK is a heterotrimeric enzyme composed by an a-catalytic subunit and two regulatory subunits, beta and gamma It is regulated by several mechanisms, including indirect activators such as metformin and direct activators such as compound A-769662. The crystal structure of AMPK bound to A-769662 has been recently reported, suggesting a hypothetical allosteric mechanism of AMPK activation assisted by phosphorylated Ser108 at the beta-subunit. Here, we have studied the direct activation mechanism of A-769662 by means of molecular dynamics simulations, suggesting that the activator may act as a glue, coupling the dynamical motion of the beta-subunit and the N-terminal domain of the a-subunit, and assisting the preorganization of the ATP-binding site. This is achieved through the formation of an allosteric network that connects the activator and ATP-binding sites, particularly through key interactions formed between aAsp88 and beta Arg83 and between beta pSer108 and aLys29. Overall, these studies shed light into key mechanistic determinants of the allosteric regulation of this cellular energy sensor, and pave the way for the fine-tuning of the rational design of direct activators of this cellular energy sensor.