#GTP hydrolysis

Cytoskeleton

What is the role of GTP hydrolysis in microtubule assembly?

Microtubules do not require GTP hydrolysis to polymerize hydrolysis follows incorporation and modulates stability rather than providing assembly energy which is entropically driven. After alpha beta dimer carrying GTP on beta adds to plus end longitudinal contacts induce GTPase activity converting beta bound GTP to GDP plus inorganic phosphate retained initially as GDP Pi lattice. GDP tubulin prefers bent conformation by about 12 degrees but constrained straight within wall creating mechanical strain stored as elastic energy. As long as terminal layers retain GTP cap maintains stabilizing influence over underlying strained lattice. When addition slows or stochastic fluctuations expose GDP layers at tip strain released protofilaments splay outward lateral bonds break rapid depolymerization ensues known as catastrophe releasing stored energy. Thus hydrolysis acts as timer converting stable polymer into unstable intermediate powering dynamic instability required for exploratory search and generating polymerization force harnessed at kinetochores and cortical force generation for spindle positioning.

Ref: Desai & Mitchison, Annu Rev Cell Dev Biol 1997 – GTP hydrolysis causing depolymerization and catastrophe timer.

View Details

Protein Sorting and Trafficking

The major energy source for nuclear transport is:

Energy input driving selective accumulation of proteins inside nucleus does not come from kinesin ATP hydrolysis used for microtubule transport or proton motive force powering mitochondrial import, but from compartmentalized GTP turnover of Ran. RCC1 guanine exchange factor bound to nucleosomes continuously recharges Ran-GDP to Ran-GTP using nuclear GTP pool, while cytoplasmic RanGAP1 SUMOylated and anchored to RanBP2/Nup358 plus co-activator RanBP1 hydrolyze GTP outside. Each import cycle consumes one GTP upon export complex disassembly in cytosol, and each export cycle consumes GTP as Ran-GTP hydrolyzed after cargo release, with turnover estimated thousands per minute in active cell. NTF2 imports Ran-GDP to sustain supply. Although DEAD-box helicases consume ATP to remodel exported mRNPs via Dbp5, primary cost for karyopherin-mediated protein flux remains GTP hydrolysis. Ubiquitin-mediated proteolysis and ATP-dependent chaperones act elsewhere. Thus GTP hydrolysis by Ran uniquely powers directionality, accumulation against gradient and receptor recycling, analogy to ATP in vesicle budding but chemically distinct using small GTPase asymmetry across nuclear envelope to bias cargo-receptor affinity transitions and compartment identity.

Ref: NCBI Bookshelf, Molecular Biology of the Cell, Section: GTP Hydrolysis by Ran as Energy Source.

View Details

Cell Signaling GPCR Pathways - I

Primary role of GTPase activity of Gα is

signal termination, 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)

View Details

Cell Signaling Fundamental PrinciplesI

GAP inactivates Ras by

hydrolyzing 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)

View Details