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• Signal transduction at the intracellular domain of transmembrane receptors, including recognition of taste, smell and light.
• Protein biosynthesis (aka translation) at the ribosome.
• Control and differentiation during cell division.
• Translocation of proteins through membranes.
• Transport of vesicles within the cell. (GTPases control assembly of vesicle coats).

1 Mechanism of GTP hydrolysis

The hydrolysis of the γ phosphateIn chemistry, a phosphate is a polyatomic ion or radical consisting of one phosphorus atom and four oxygen. In the ionic form, it carries a -3 formal charge, and is denoted PO3-. In a biochemical setting, a free phosphate ion in solution is called inorgan of GTP supposedly occurs by the S_N2 mechanism (see nucleophilic substitution) via a pentavalent intermediate state depending on Mg²⁺Magnesium is the chemical element in the periodic table that has the symbol Mg and atomic number 12. Magnesium is the eighth most abundant element and constitutes about 2% of the Earth's crust, and it is the third most plentiful element dissolved in seawa.

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2 Regulatory GTPases

Regulatory GTPases, also called the GTPase superfamilyThe GTPase superfamily is a superfamily of switch proteins. Members Sar1 ARF Rab., are GTPases used for regulation of other biochemicalBiochemistry is the chemistry of life. Biochemists study the elements, compounds and chemical reactions that are controlled by enzymes and take place in all living organisms. Biochemistry is focused on the structure and function of cellular components, su processes. Most prominent among the regulatory GTPases are the G proteins.

2.1 GTP switch

All regulatory GTPases have a common mechanism that enables them to switch a signal transduction chain on and off. Throwing the switch is performed by the unidirectional change of the GTPase from the active, GTP-bound form to the inactive, GDPGDP ( guanosine di phosphate) is a chemical compound essential to signal transduction in living cells. It is created by the actions of GTPases on GTP. Nucleotides.-bound form by hydrolysis of the GTP through intrinsic GTPase-activity, effectively switching the GTPase off. This reaction is initiated by GTPase-activating protein s (GAPs), coming from another signal transduction pathway. It can be reverted (switching the GTPase on again) by Guanine nucleotide exchange factor s (GEFs), which cause the GDP to dissociate from the GTPase, leading to its association with a new GTP. This closes the cycle to the active state of the GTPase; the irreversible hydrolysis of the GTP to GDP forces the cycle to run only in one direction. Only the active state of the GTPase can transduce a signal to a reaction chain.

2.2 Switch regulation

The efficiency of the signal transduction via a GTPase depends on the ratio of active to inactive GTPase. That equals

with k_diss.GDP being the dissociation constant of GDP, and k_cat.GTP the hydrolysis constant of GTP for the specific GTPase. Both constants can be modified by special regulatory proteins.
The amount of active GTPase can be changed in several ways :

1. Acceleration of GDP dissociation by GEFs speeds up the building of active GTPase.
2. Inhibition of GDP dissociation by guanine nucleotide dissociation inhibitor s (GDIs) slows down the building of active GTPase.
3. Acceleration of GTP hydrolysis by GAPs reduces the amount of active GTPase.
4. GTP analogues like γ-S-GTP, β,γ-methylene-GTP, and β,γ-imino-GTP that cannot be hydrolized fixate the GTPase in its active state.

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Topics: GTPase Gtpase Proteins Gtp Signal Gtpases Active Protein Family...

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GTPaseGTPases are a large family of enzymes that can bind and hydrolyze GTP. The GTP binding and hydrolysis takes place in the highly conserved G domain common to all GTPases. GTPases play an important role in: Signal transduction at the intracellular domain of GTPase superfamilyThe GTPase superfamily is a superfamily of switch proteins. Members Sar1 ARF Rab.