Investigation of Structural Differences Between the Oncogenic Mutants of KRas 4B

K-Ras is a membrane-associated GTPase that is frequently mutated in cancer. The incidence of K-Ras mutation is close to 90% and 50% in pancreatic and colorectal cancer, respectively. Most commonly, mutations occur at position 12, replacing a glycine with either aspartate or valine and inhibiting GTP hydrolysis. GTP-bound K-Ras recruits effector proteins, such as Raf and PI3 kinases, and initiates signaling to promote cell proliferation, survival, and motility. While G12D is the most frequent oncogenic mutation in K-Ras, G12V K-Ras is associated with a highly aggressive and drug resistant cancer phenotype. Accumulating evidence suggests that different oncogenic mutations in K-Ras activate distinct signaling pathways responsible for variability in tumorigenic potential and resistance to chemotherapy. Although structural features distinguishing G12V from G12D K-Ras are expected, recent X-ray crystallography studies of GDP- bound mutant proteins did not reveal significant differences.However, K-Ras mutants may differ in their ability to sample the conformational space in solution, while only one conformer exists in the crystal. Our preliminary data suggests that G12V but not G12D K-Ras-GDP exists in two slowly exchanging conformations in solution, one of which resembles “active” GTP-bound Ras, while neither wild type nor G12D K-Ras exhibits similar conformational exchange. This active-like conformer in the GDP-bound state interacts with Ca2+-regulator Calmodulin. Here, a model of the structure of K-Ras G12V (GDP)-CaM complex has been presented.