Fig. 3. Design of a system in MEK1 for Lan stapling. (a) Site directed mutagenesis scheme to generate protein substrates in the design of a Lan staple. Wild type (wt) MEK1 (PDB 3W8Q) has six native free Cys residues (black, grey & red) and two activating Ser sites 218 (cyan) & 222 (blue). (b) Predicted side-chain reactive accessibility of sites 218 and 222 with and without ADP + Mg(ii).