Crystal structures of MAP kinase p38 complexed to the docking sites on its nuclear substrate MEF2A and activator MKK3b.
Chang CI, Xu BE, Akella R, Cobb MH, Goldsmith EJ, Mol Cell, 2002 Jun - link

Hydrophobic as well as charged residues in both MEK1 and ERK2 are important for their proper docking.
Xu Be, Stippec S, Robinson FL, Cobb MH, J Biol Chem, 2001 Jul 13 - link