Fig. 9. Structural analysis of SPE-ERK2. (A) Electrostatic surface presentation of WT-ERK2 and SPE-ERK2 of the C'-lobe. The SPS region (circled) display increased electonegativity due to the S246E mutation, which could have an effect on importin7 recognition. (B) ERK2- CK2 binding model. (I) The available crystal structure of human CK2α (PDB code: 2PVR) (blue) with two sulfate ions in the P+1 site (green) and P+3 site (red) are located in a 10.7Å apart. Amino acid important for substrate recognition pocket are shown and labeled. (II) The MAP kinase insert of the SPS region of ERK2 and the side chains of Ser-246, Gln-247, Glu-248, and Asp-249 are shown in orange (orange). The distance between the side chains of Gln-247 and Glu-248 is measured to be 10.7Å similar to that of sulfate ions in the CK2 active site. (III) The structures of ERK2 and CK2 were pair fitted on Gln-247 and Glu-248 (ERK2) to the P+1 and P+3 sulfate ions from CK2 which exhibit an almost perfect fit introducing Ser-246 into the active site (note that no calculation was conducted). In this regard, Ser-246 Oγ is located 6.11Å from Asp-156 Oδ1 yet with minimal conformational change is the side chains conformation a distance acceptable for polar interaction could be reached.