Protein AMPylation by an Evolutionarily Conserved Pseudokinase

Abstract

Summary Approximately 10% of human protein kinases are believed to be inactive and named pseudokinases because they lack residues required for catalysis. Here we show that the highly conserved pseudokinase selenoprotein-O (SelO) transfers AMP from ATP to Ser, Thr and Tyr residues on protein substrates (AMPylation), uncovering a previously unrecognized activity for a member of the protein kinase superfamily. The crystal structure of a SelO homolog reveals a protein kinase-like fold with ATP flipped in the active site, thus providing a structural basis for catalysis. SelO pseudokinases localize to the mitochondria and AMPylate proteins involved in redox homeostasis. Consequently, SelO activity is necessary for the proper cellular response to oxidative stress. Our results suggest that AMPylation may be a more widespread post translational modification than previously appreciated and that pseudokinases should be analyzed for alternative transferase activities.

Cellular microbiology: Bacterial toxin interference drives understanding of eukaryotic cell function

“…Until recently, pseudokinases were considered inactive enzymes lacking one conserved residue known to bind and hydrolyse ATP. Recent crystal structure determination of selenoprotein O (SelO) from Pseudomonas syringae reveals that it adopts a kinase‐like structure with an atypical flipped position of ATP as compared to canonical enzymatic sites found in kinases (Sreelatha et al, ). This particular presentation of the nucleotide correlates with SelO in vitro AMPylation activity of hydroxyl groups of serine, threonine, and tyrosine amino‐acid residues.…”

“…Eukaryotic homologues of SelO have at their amino terminus a functional domain for a targeting to mitochondria. The identification of SelO targets, notably the thioredoxin‐like protein glutaredoxin, made it possible to identify the function of SelO in the regulation of S‐glutathionylation‐mediated protection of cells against oxidative stress (Sreelatha et al, ). This reversible oxidation of cysteine residues on proteins provides a protective mechanism of cells against oxidative stress.…”

“…Recent findings have shown that huntingtin yeast-interacting protein E stimulates the alpha-synuclein, thereby preventing its aggregation, a neuroprotective response that could be exploited in the treatment of (Sreelatha et al, 2018). This reversible oxidation of cysteine residues on proteins provides a protective mechanism of cells against oxidative stress.…”

Flipping ATP to AMPlify Kinase Functions

“…In this issue of Cell , Sreelatha et al (2018) describe how one pseudokinase transfers adenosine monophosphate (AMP) rather than phosphate to protein substrates, revealing unexpected catalytic diversity for the kinase fold. …”

“…But, we should not ignore the possibility that some pseudoenzymes may have been repurposed to catalyze other reactions. Indeed, in this issue of Cell , work by Sreelatha et al (2018) reminds us not to let our thinking about possible enzyme activities be constrained by the predicted protein fold.…”