GTPase cycle

These GTPases cycle between inactive GDP-bound forms and active GTP-bound forms. Eukaryotic-specific domain families have evolved that either promote GTPase activities (GTPase activator proteins, GAPs ) or promote exchange of GDP for GTP (guanine nucleotide exchange... 

Selected entries from Methods in Enzymology [vol, page(s)] Analysis of GTP-binding/GTPase cycle of G protein, 237, 411-412 applications, 240, 216-217, 247 246, 301-302 [diffusion rates, 246, 303 distance of closest approach, 246, 303 DNA (Holliday junctions, 246, 325-326 hybridization, 246, 324 structure, 246, 322-324) dye development, 246, 303, 328 reaction kinetics, 246, 18, 302-303, 322] computer programs for testing, 240, 243-247 conformational distribution determination, 240, 247-253 decay evaluation [donor fluorescence decay, 240, 230-234, 249-250, 252 exponential approximation of exact theoretical decay, 240, 222-229 linked systems, 240, 234-237, 249-253 randomly distributed fluorophores, 240, 237-243] diffusion coefficient determination, 240, 248, 250-251 diffusion-enhanced FRET, 246, 326-328 distance measurement [accuracy, 246, 330 effect of dye orientation, 246, 305, 312-313 limitations, 246,... 

At least three different GTPase states can be differentiated in the GTPase cycle the active GTP form, the inactive GDP form and an empty form of the GTPase, which is generally a short-lived state. 

Fig. 9.2. The GTPase cycle of the Ras protein. Conversion of the inactive Ras GDP complex into the active Ras GTP complex is brought about by guanine nucleotide exchange factors (GEFs). The activated state of the Ras protein is terminated by hydrolysis of the bound GTP. The help of a GTPase actvating protein (GAP) is required, due to the intrinsically slow GTPase activity of the Ras protein. Ras protein performs all its functions in close association with the cell membrane. It carries a membrane anchor and the effector proteins preceding and following in sequence are also associated with the membrane.

Cassel, D., Levkovitz, H., and Selinger, Z. (1977). The regulatory GTPase cycle of turkey erythrocyte adenylate cyclase./ Cyclic Nucleotide Res. 3, 393-406. 

Fig. 2. Summary of regulatory GTPase cycle in photoactivation of cGMP-specific phosphodiesterase (PDE) in retinal rod cells. T, transducin (Gt) Rho, rhodopsin Rho, photoactivated Rho. PDE is represented as a heterotrimeric peripheral membrane protein, as is T. This regulatory cycle differs from that in Fig. 1 mainly in that the activation of PDE entails the dissociation of an inhibitory y subunit (PDEy) under the influence of activated Ta-GTP complex leading to formation of intermediary soluble Ta-GTP/PDEy complex. This complex persists until GTP is hydrolyzed to GDP, at which moment the inhibited PDEa/3y heterotrimer reforms. Dark adapted - non-activated - Rho is then required for reassociation of Ta-GDP to T/3y and release of GDP.

Leonard DA, Evans T, Hart M, Cerione RA, Manor D. Investigation of the GTP-binding/GTPase cycle of cdc42hs using fluores- 58. cence spectroscopy. Biochemistry. 1994 33 12323-12328. 

Fig. 1. ADP-ribosylafion of Rho by C3 transferases. Rho proteins are regulated by a GTPase cycle. The GTP-binding proteins ore inactive with GDP bound, and active in the GTP-bound form. GDP/GTP exchange is facilitated by guanine nucleotide dissociation stimulator(s) (GDS) and inhibited by guanine nucleotide dissociation inhibitor(s) (GDI). In the active form, Rho protein interacts with its effector(s) and induces several cellular responses, one of which is polymerization of actin. Rho is ADP-ribosylated by C3 transferases at asparagine-41. Most likely, the modification inhibits the interaction of Rho with its effector(s) which results in inhibition of Rho dependent processes (e.g. F-actin depolymerization)...

Along the GTPase cycle, the / y-complex contacts at least three types of signaling proteins the Ga-subunit, the activated receptor and the ySy-specific effector proteins. 

Fig. 12.6. Diagram of a GTPase cycle and subunit association/dissociation proposed to control signal transduction between muscarinic G protein-coupled receptors and the effector. The ACh-receptor interaction facilitates GTP binding and activates the a subunit. The a subunit-GTP complex then dissociates from the (By subunit, and each is free to activate effector proteins. The duration of separation is determined by the rate of a subunit-mediated GTP hydrolysis.

Fig. 15.1.2. The GTPase cycle showing activation of GTPase by guanine exchange factors (GEFs) in the presence of GTP and inactivation by hydrolysis of GTP to GDP in the presence of GTPase activating proteins (GAPs).

Figure 6.2 Rab cycle through coordination between the GTPase cycle and the cycle of membrane attachment and detachment. Rab proteins are intrinsicaiiy soiubie and require a posttransiationai modification for membrane association. They first associate with REP and form a compiex that is the substrate for the subsequent duai prenylation of C-terminai cysteines by a heterodimetic RabGGTase (RabGGTa and B). After lipid transfer, REP deiivers the prenylated Rab to the membrane. The cyciing of prenylated...

The assembly-disassembly cycle of CO PI and COPII coats is controlled by the GTPase cycle of the small G proteins Arfl and Sar. We describe here two spectroscopic assays that enable real-time studies of some elementary steps of coat assembly and disassembly on artificial liposomes of defined composition and curvature. A flotation assay to assess the effect of membrane curvature on protein adsorption to liposomes is also presented. 

C. B. Marshall, D. Meiri, M. J. Smith, M. T. Mazhab-Jafari, G. M. C. Gasmi-Seabrook, R. Rottapel, V. Stambolic and M. Ikura, Probing the GTPase Cycle with Real-Time NMR GAP and GEF Activities in Cell Extracts, Methods, 2012, 57, 473. 

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