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Introduction
Biological molecular machines are complex and play a crucial role in regulating cellular processes. These machines are categorized into ATPases and GTPases based on their primary energy sources. Kinesin, myosin, dynein, and chromatin remodeling proteins are well-known ATPases. In previous studies, the photo-reversible control of kinesin Eg5 has been achieved using an azobenzene derivative 1,2. There are more than 100 GTP-binding proteins in mammalian cells that act as biological timers and regulate various biological processes.
Ras proteins belong to a superfamily of small monomeric GTPases that function as a molecular binary switch 3. The binary switch behavior of Ras has been shown to be active upon binding to GTP and inactive upon binding to GDP. As the release of GDP and hydrolysis of GTP by Ras are slow (GTP hydrolysis rate constant: 0.028 min-1, GDP dissociation rate constant: 0.079 min-1) 4, the switch-like function is accelerated by interactions with specific protein-binding partners, guanine nucleotide exchange factor (GEF) and guanine accelerate protein (GAP). In the Ras-GTP cycle, GEFs promote the release of GDP from Ras, whereas GAPs promote the hydrolysis of GTP inside Ras (Figure 1). Collectively, GEFs and GAPs accelerate the GTP hydrolysis rate by approximately 100,000 times 5.
Ras, via various downstream effector enzymes, regulates cellular signal transduction pathways implicated in cell growth, apoptosis, migration, and differentiation 3,6. Activated Ras has a high affinity for downstream proteins, such as the serine/threonine kinase Raf. After binding to Ras, Raf activates the mitogen-activated protein kinase (MAPK) extracellular signal-regulated kinase pathway to control cell cycle progression and differentiation 7. Therefore, the regulation of Ras activity is crucial for controlling cell cycle progression.
Ras expressed in diverse mammalian tissues, which are encoded by three analogous genes: Harvey Ras (HRas), Kirsten Ras (KRas), and neural Ras (NRas)8. Ras consists of a G-domain at the N-terminus and a hypervariable region (HVR) at the C-terminus. The G domain contains two switch regions, region Ⅰ (30-37 aa) and region Ⅱ (60-76 aa), which have GTP and GDP binding ability, enabling Ras to function as a molecular switch. The HVR (167-187 aa) is unstructured and may change Ras from a monomer to a multimer when 2-nitrobenzyl...