GEF-independent Ran activation shifts a fraction of the protein to the cytoplasm and promotes cell proliferation

Ras S89D mutation induced allosteric changes that promoted its nucleotide exchange and signaling activation

The small GTPase Ras is among the most frequently mutated genes and its mutations often drive oncogenesis across various cancers. While the role of NRas phosphorylation at S89 in the context of a Q61R mutation in melanoma genesis remains controversial, the impact of S89 phosphorylation on NRas function has not been fully elucidated. In this study, we employed the S89D phosphorylation-mimetic mutation and demonstrated that the S89D mutation alone activated all Ras isoforms by increasing the GTP-bound population, thereby promoting ERK phosphorylation and cell proliferation. The S89D mutant retained unaltered hydrolysis kinetics and GTP/GDP relative affinity but exhibited an accelerated intrinsic nucleotide exchange rate, due to impaired nucleotide binding. A 1.2 Å crystal structure of the S89D mutant revealed substantial local conformational changes, as well as alterations propagating to the nucleotide-binding pocket, providing a structural basis for the observed biochemical properties. Collectively, these findings established that the S89D mutation activated Ras by enhancing intrinsic nucleotide exchange, offering new insights into Ras allostery.

In-silico and In-vitro Evaluation of Novel Carboxamide Analogue on the Metastasis of Triple Negative Breast Cancer Cells Utilizing Novel PCPTC-loaded PEGylated-PLGA Nanocarriers

This study aimed to determine the effects of novel N-{3-[(pyridin-4-yl)carbamoyl] phenyl} thiophene-2-carboxamide or PCPTC chemical moiety loaded Poly(lactic-co-glycolic acid)-Poly (Ethylene glycol) or (PLGA-PEGylated) NP as an anti-metastatic Ran GTPase therapeutic agent on MDA-MB231 triple-negative human breast cancer cells. Molecular docking and MD simulation was done to determine the binding potential of novel carboxamide PCPTC with Ran GTPase. PLGA and PLGA-PEG based NP encapsulating PCPTC were fabricated using the Modified Double Emulsion Solvent Evaporation Technique and characterized for size, zeta potential, polydispersity and morphology. In vitro evaluation of loaded nanoparticles such as cellular localization study, cell proliferation, cell migration, cell invasion and Ran Pull Down assay were carried out on MDA-MB231 breast cancer cells. Ran downregulation was determined by pull down assay. PCPTC with Ran GTPase exhibited strong structural stability based on in silico analysis. The average sizes of PCPTC loaded NP ranged between 166.3 nm to 257.5 nm and were all negatively charged. Scanning electron microscopy data showed that loaded NP were smooth and spherical. Fluorescence microscopy data confirmed the intracellular localization of loaded nanoparticles inside the MDA-MB231 cells. Cell proliferation assay (MTT assay) confirmed the cytotoxic effect of the loaded-NP when compared to blank nanoparticles. PCPTC-loaded NP inhibited metastasis and invasion of MDA-MB231 cells. This anti-metastatic and the anti-invasive effect was due to the Ran GTPase cycle blockage, which was confirmed by performing Ran Pull down assay. we propose that PCPTC is a promising compound to inhibit Ran GTPase and may act as a potential therapeutic agent against breast cancer. PCPTC-loaded NP successfully stopped the metastasis of MDA-MB231 cells by disrupting the Ran cycle.

Emerging role of small GTPases and their interactome in plants to combat abiotic and biotic stress

Plants are frequently subjected to abiotic and biotic stress which causes major impediments in their growth and development. It is emerging that small guanosine triphosphatases (small GTPases), also known as monomeric GTP-binding proteins, assist plants in managing environmental stress. Small GTPases function as tightly regulated molecular switches that get activated with the aid of guanosine triphosphate (GTP) and deactivated by the subsequent hydrolysis of GTP to guanosine diphosphate (GDP). All small GTPases except Rat sarcoma (Ras) are found in plants, including Ras-like in brain (Rab), Rho of plant (Rop), ADP-ribosylation factor (Arf) and Ras-like nuclear (Ran). The members of small GTPases in plants interact with several downstream effectors to counteract the negative effects of environmental stress and disease-causing pathogens. In this review, we describe processes of stress alleviation by developing pathways involving several small GTPases and their associated proteins which are important for neutralizing fungal infections, stomatal regulation, and activation of abiotic stress-tolerant genes in plants. Previous reviews on small GTPases in plants were primarily focused on Rab GTPases, abiotic stress, and membrane trafficking, whereas this review seeks to improve our understanding of the role of all small GTPases in plants as well as their interactome in regulating mechanisms to combat abiotic and biotic stress. This review brings to the attention of scientists recent research on small GTPases so that they can employ genome editing tools to precisely engineer economically important plants through the overexpression/knock-out/knock-in of stress-related small GTPase genes.

A complete allosteric map of a GTPase switch in its native cellular network

Allosteric regulation is central to protein function in cellular networks. A fundamental open question is whether cellular regulation of allosteric proteins occurs only at a few defined positions or at many sites distributed throughout the structure. Here, we probe the regulation of GTPases-protein switches that control signaling through regulated conformational cycling-at residue-level resolution by deep mutagenesis in the native biological network. For the GTPase Gsp1/Ran, we find that 28% of the 4,315 assayed mutations show pronounced gain-of-function responses. Twenty of the sixty positions enriched for gain-of-function mutations are outside the canonical GTPase active site switch regions. Kinetic analysis shows that these distal sites are allosterically coupled to the active site. We conclude that the GTPase switch mechanism is broadly sensitive to cellular allosteric regulation. Our systematic discovery of new regulatory sites provides a functional map to interrogate and target GTPases controlling many essential biological processes.