The RIO kinase (IPR000687) is an atypical protein kinase that is classified as such due to its low sequence similarity to eukaryotic protein kinases. The conformation of ATP when bound to RIO kinase is distinct from that of ePKs (such as serine/threonine kinases or insulin receptor tyrosine kinases). This suggests that the detailed mechanism of catalytic aspartate involved in RIO kinase phosphorylation may differ from the mechanism employed by known serine/threonine ePKs.