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#actin cytoskeleton

6 public questions tagged with this topic.

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. Rac1 activation downstream of PI3K produces WAVE Arp2/3 dependent lamellipodia, Cdc42 activates N WASP Arp2/3 filopodia. Ran GTP gradient formed around chromosomes by RCC1 GEF controls spindle assembly and nuclear import export through importins, Rab GTPases mark endosomal compartments guiding vesicle trafficking via tethering complexes like HOPS CORVET. Experiments with C3 exoenzyme ADP rybosylating Rho abolish stress fibers, confirming Rho GTP drives actin rearrangements in HeLa and many non muscle cells responding to cues.

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

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Cytoskeleton

The actin cytoskeleton in prokaryotic cells is functionally similar to which of the following eukaryotic proteins?

Prokaryotic cells maintain rod shape and organize cell wall synthesis without eukaryotic compartments using cytoskeletal homologs sharing ancient ATPase fold. MreB, belonging to actin Hsp70 superfamily, shares structural core of five conserved sequence motifs forming ATP binding pocket between domains IA and IIA. Purified MreB polymerizes into ATP dependent antiparallel double filaments that rotate circumferentially beneath cytoplasmic membrane driven by cell wall elongation machinery. It scaffolds elongasome complex containing RodA glycosyltransferase, PBP2 transpeptidase and MreC MreD, directing insertion of new peptidoglycan hoops to maintain lateral wall. Depletion or inhibition by small molecule A22 causes rod to sphere transition confirming morphogenetic role, similar to actin controlling shape in eukaryotes. Keratin and vimentin are metazoan intermediate filament proteins absent in most bacteria and archaea, while ActA is Listeria monocytogenes surface protein that activates host Arp2/3 complex to form actin comet tails for motility, not bacterial cytoskeleton. Thus prokaryotic actin analog best matching functional criteria is MreB protein.

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 16: Cytoskeleton and Bacterial Homologs MreB.

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Cell Communication

Integrin molecules link ECM to actin cytoskeleton. Integrins bind to which ECM macromolecule? (June 2012)

Fibronectin, 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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Cell Communication and Cell Adhesion

Dystrophin links actin cytoskeleton to

Dystroglycan–ECM complex, 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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Cell Communication and Cell Adhesion

Which adaptor protein links integrins to actin?

Vinculin, 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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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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