Atypical MAPK protein. Phosphorylates microtubule-associated protein 2 (MAP2) and MAPKAPK5. The precise role of the complex formed with MAPKAPK5 is still unclear, but the complex follows a complex set of phosphorylation events
This is due to mk5-dependent phosphorylation and only this retarded erk4 species is both phosphorylated on ser(186) and co-immunoprecipitates with wild-type mk5. We conclude that binding between erk4 and mk5 facilitates phosphorylation of ser(186) and stabilization of the erk4-mk5 complex.