UCSF

RAS proteins cycling between the active-form (GTP-bound) and inactive-form (GDP-bound) play a key role in cell signaling pathways that control cell survival, proliferation, and differentiation. Mutations at codon 12, 13, and 61 in RAS are known to attenuate its GTPase activity favoring the RAS active state and constitutively active downstream signaling. This hyperactivation accounts for various malignancies including pancreatic, lung, and colorectal cancers. Active KRAS is found to exist in equilibrium between two rapidly interconverting conformational states (State1-State2) in solution. Due to this dynamic feature of the protein, the ¹H-¹⁵N correlation cross-peak signals of several amino acid (AA) residues of KRAS belonging to the flexible loop regions are absent from its 2D ¹H-¹⁵N HSQC spectrum within and near physiological solution pH. A threonine to serine mutation at position 35 (T35S) shifts the interconverting equilibrium to State1 conformation and enables the emergence of such residues in the 2D ¹H-¹⁵N HSQC spectrum due to gained conformational rigidity. We report here the ¹H^N, ¹⁵N, and ¹³C backbone resonance assignments for the 19.2 kDa (AA 1-169) protein constructs of KRAS-GppNHp harboring T35S mutation (KRAS^T35S/C118S-GppNHp) and of its oncogenic counterpart harboring the Q61L mutation (KRAS^{T35S/Q61L/C118S}-GppNHp) using heteronuclear, multidimensional NMR spectroscopy at 298 K. High resolution NMR data allowed the unambiguous assignments of ¹H-¹⁵N correlation cross-peaks for all the residues except for Met1. Furthermore, 2D ¹H-¹⁵N HSQC overlay of two proteins assisted in determination of Q61L mutation-induced chemical shift perturbations for select residues in the regions of P-loop, Switch-II, and helix α3.