Recombinant human KRAS (GTPase), isoform a, encompassing amino acids 2-186 (end). This construct contains an N-terminal His-tag (6xHis) followed by an optimal TEV protease target sequence that allows cleavage of the His-tag from the protein (TEV: tobacco etch virus cysteine protease, BPS Bioscience #50308). The recombinant protein also contains a mutation of interest, G12D. The protein was affinity purified and loaded with GDP. Unbound GDP was removed by spin column.