Figure 4.

Flipped orientation of the ATP molecule in SelO. In the active site of a canonical kinase the adenine ring is buried deep in the catalytic cleft while the phosphates are exposed. Kinases transfer the distal phosphate (farthest from the adenine ring) onto its substrates (phosphorylated) with concomitant ADP release. In SelO, the orientation of the ATP molecule is flipped, with the phosphates buried deep in the binding cleft. SelO transfers the proximal phosphate (closest to the adenine ring) onto its target (AMPylated) with pyrophosphate being the other product of the AMPylation reaction. The dashed lines represent cleavage of the bond in a phosphorylation or AMPylation reaction.