A repurposed AMP binding domain reveals mitochondrial protein AMPylation as a regulator of cellular metabolism.

Protein AMPylation, the covalent addition of adenosine monophosphate (AMP) to protein substrates, has been known as a post translational modification for over 50 years. Research in this field is largely underdeveloped due to the lack of tools that enable the systematic identification of AMPylated substrates. Here, we address this gap by developing an enrichment technique to isolate and study AMPylated proteins using a nucleotide-binding protein, hinT. Cryo-EM reconstruction of an AMPylated protein bound to hinT provides a structural basis for AMP selectivity. Using structure guided mutagenesis, we optimize enrichment to identify novel substrates of the evolutionarily conserved AMPylase, Selenoprotein O. We show that mammalian Selenoprotein O regulates metabolic flux through AMPylation of key mitochondrial proteins including glutamate dehydrogenase and pyruvate dehydrogenase. Our findings highlight the broader significance of AMPylation, an emerging post translational modification with critical roles in signal transduction and disease pathology. Furthermore, we establish a powerful enrichment platform for the discovery of novel AMPylated proteins to study the mechanisms and significance of protein AMPylation in cellular function.