Mitogen-activated protein kinase scaffold protein 1 is an enzyme identified as an interacting protein that binds specifically to MAP kinase kinase MAP2K1/MEK1 and to MAP kinase MAPK2/ERK1. This protein enhances the activation of MAPK2, and thus is thought to function as an adaptor to enhance the efficiency of the MAP kinase cascade.

When overexpressed in cultured cells, MP1 enhanced activation of ERK1 and activation of a reporter driven by the transcription factor ELK1. Expression of MP1 in cells increased binding of ERK1 to MEK1. MP1 apparently functions as an adaptor to enhance the efficiency of the MAP kinase cascade.