Expression and purification of EPHA2 tyrosine kinase domain for crystallographic and NMR studies
The receptor tyrosine kinase EPHA2 is overexpressed in several cancer entities (breast, head and neck, non-small cell lung cancer). Small molecule-based inhibition of the activity of the EPHA2 kinase domain (KD) has been seen as an important strategy for achieving therapeutic intervention. However, obtaining structural information by protein crystallography or by NMR spectroscopy aiding drug discovery, has been severely hampered due to the lack of pure and homogeneous protein. Here different fragments of the EPHA2 KD were expressed and purified from both bacterial (Escherichia coli BL21 (DE3) cells) and insect cells (Spodoptera frugiperda, Sf9 cells). [1H,15N]-HSQCs were used to determine the proper folding and homogeneity of all the constructs. E. coli expressed and purified protein constructs though well-folded were unstable and did not crystallize. However, the construct (D596-G900) produced in Sf9 cells yielded in a homogenous, well-folded and crystallized readily, resulting in eleven new EPHA2-ligand co-crystal structures. We have also established a strategy for selective and uniform 15N amino acid labeling of the EPHA2 KD in Sf9 cells for investigating dynamics and EPHA2-drug interactions by NMR.