Recombinant human KRAS (GTPase), isoform a, encompassing amino acids 2-186 (end). In this construct the N-terminal end of the protein contains a 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 protein also contains mutation of interest G12D. The protein was affinity purified and loaded with GDP. Unbound GDP was removed by spin column.