#GTPase

Cytoskeleton

Which GTPase is responsible for actin cytoskeleton rearrangements in HeLa cells?

Signal transduction from extracellular matrix and chemokines to actin cytoskeleton uses small GTPases of Rho subgroup cycling between GDP bound passive cytosolic state bound to GDI and GTP active membrane state driven by GEFs. In HeLa cervical carcinoma cells stimulated with lysophosphatidic acid or serum, RhoA GTP rapidly accumulates activating effectors ROCK1 2 that phosphorylate myosin light chain and LIMK restricting cofilin severing, and mDia1 formin nucleating unbranched filaments. Outcome is assembly of contractile stress fibers anchored at focal adhesions and enhanced cortical tension.

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 16: Rho GTPases and Actin Remodeling.

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Protein Sorting and Trafficking

Which GTPase is specifically involved in nuclear transport?

Ran is small 25 kilodalton Ras-family GTPase that specializes in marking nuclear versus cytoplasmic compartments, unlike Rab, Rho and Ras which control vesicle docking, actin remodeling and MAP kinase signaling elsewhere. Its nucleotide state differs across envelope because regulators are spatially segregated: RCC1 guanine nucleotide exchange factor bound to histones H2A-H2B inside nucleus generates high Ran-GTP, while RanGAP1 SUMOylated and anchored to RanBP2/Nup358 at cytoplasmic filaments together with RanBP1 accelerate GTP hydrolysis outside producing Ran-GDP. This partitioning creates ste

Ref: Alberts et al., Molecular Biology of the Cell, 6th ed., Chapter 12: Ran GTPase Gradient, RCC1 and RanGAP.

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Protein Sorting and Trafficking

Ran-GTP is primarily involved in:

Directionality of nucleocytoplasmic transport relies on asymmetric distribution of small GTPase Ran nucleotide states forming gradient across nuclear envelope. Regulator RCC1 RanGEF bound to chromatin generates high Ran-GTP concentration inside nucleus through exchange of GDP for GTP, while cytoplasmic filaments of nuclear pore complex associated with RanGAP and RanBP1 stimulate GTP hydrolysis to Ran-GDP in cytosol, depleting Ran-GTP outside. Importin alpha/beta-cargo complexes formed in cytoplasm traverse pore via interactions with FG nucleoporins, encountering Ran-GTP in nucleus which binds

Ref: Gorlich & Kutay, Annu Rev Cell Dev Biol 1999, Ran Gradient. Alberts 7th ed., Chapter 12, Transport.

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A Cell Signaling

Overexpression of which GTPase in GTP-bound form modulates actin cytoskeleton?

Rho (GTP), is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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