Expression, purification and characterization of inactive and active forms of ERK2 from insect expression system

• Inactive and active ERK2 production method in insect system is newly developed.
• Inactive ERK2 expressed in insect system is homogenously unphosphorylated.
• Protein yield of ERK2 from insect cells is 20-fold higher than that from E. coli.
• Active ERK2 is produced by in vivo co-expression in insect system with MEK1.
• Kinase function of purified ERK2 is confirmed by biochemical activity assay.

Extracellular signal-regulated kinase 2 (ERK2) is a serine/threonine protein kinase involved in many cellular programs, such as cell proliferation, differentiation, motility and programed cell-death. It is therefore considered an important target in the treatment of cancer. In an effort to support biochemical screening and small molecule drug discovery, we established a robust system to generate both inactive and active forms of ERK2 using insect expression system. We report here, for the first time, that inactive ERK2 can be expressed and purified with 100% homogeneity in the unphosphorylated form using insect system. This resulted in a significant 20-fold yield improvement compared to that previously reported using bacterial expression system. We also report a newly developed system to generate active ERK2 in insect cells through in vivo co-expression with a constitutively active MEK1 (S218D S222D). Isolated active ERK2 was confirmed to be doubly phosphorylated at the correct sites, T185 and Y187, in the activation loop of ERK2. Both ERK2 forms, inactive and active, were well characterized by biochemical activity assay for their kinase function. Inactive and active ERK2 were the two key reagents that enabled successful high through-put biochemical assay screen and structural drug discovery studies.