Ras signaling: The structure and function of K-Ras4B

Authors

• H Jang
• R Nussinov

Abstract

Ras is a small GTPase, controlling signal transduction pathways and promoting cell proliferation and survival. KRAS is frequently mutated in cancer. Ras consists of highly homologous catalytic domains and flexible C-terminal hypervariable regions (HVRs) that differ significantly across Ras isoforms. Ras activation is regulated by guanine nucleotide exchange factors that catalyze the exchange of GDP by GTP, and inactivation is terminated by GTPase-activating proteins that accelerate the intrinsic GTP hydrolysis rate by orders of magnitude. Ras has multiple partners, signals through several key pathways and fulfills critical functions in the cell life. Mutations in Ras are common in a variety of cancers; yet it is still undruggable. Here, using MD simulations we modeled K-Ras4B membrane interaction and dimerization. Membrane binding of K-Ras4B through the anchoring of the positively charged HVR is thought to be critical to its function as an oncogene and initiates signaling events. Remarkably, K-Ras4B-GTP, but not GDP-bound, is able to form stable homodimers with different dimer interfaces, suggesting that the nucleotide-dependent dimerization with various dimer interfaces can resolve nanoclustering and cluster reorganization accomplishment with Raf's activation. Ras was believed to function as a monomer; however, since Raf dimerizes, it has been suspected that Ras can also dimerize. Dimerization and clustering could rein the fluctuations producing more productive pre-organized conformations.

Scientific Focus Area: Molecular Biology and Biochemistry

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