MAPK ERK5 BMK1 ERK5, also known as big MAP kinase 1 (BMK1), is twice the size of other MAPKs. The amino-terminal half contains the kinase domain, which is similar to that of ERK1/2 and has the TEY activation motif, whereas the carboxy-terminal half is unique. MEK5 phosphorylates and activates ERK5, and then the activated ERK5 phosphorylates substrates including myocyte enhancer factor 2 (MEF2). IMR:0100216 molecule_role