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Encyclopedia > GTPase

GTPases 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: Ribbon diagram of the enzyme TIM. TIM is catalytically perfect, meaning its conversion rate is limited, or nearly limited to its substrate diffusion rate. ... Hydrolysis is a chemical process in which a molecule is split into two parts by the addition of a molecule of water. ... Guanosine triphosphate (GTP) is also known as guanosine-5-triphosphate. ... Conservation may refer to the following: In science: Conservation laws, in physics, states that a particular measurable property of an isolated or closed physical system does not change as the system evolves. ... Within a protein, a structural domain (domain) is an element of overall structure that is self-stabilizing and often folds independently of the rest of the protein chain. ...

Contents

In biology, signal transduction is any process by which a cell converts one kind of signal or stimulus into another. ... The seven transmembrane α-helix structure of a G protein-coupled receptor. ... An overview of protein synthesis. ... Translation in the cytoplasm; tRNA carries amino acids which are added to the growing peptide chain in the ribosome. ... Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ... Embryonic stem cells differentiate into cells in various body organs. ... This article or section does not cite its references or sources. ... Chromosomal translocation of the 4th and 20th chromosome. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Drawing of a cell membrane A component of every biological cell, the selectively permeable cell membrane (or plasma membrane or plasmalemma) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. ... Cells in culture, stained for keratin (red) and DNA (green). ...


Mechanism of GTP

The hydrolysis of the γ phosphate of GTP supposedly occurs by the SN2 mechanism (see nucleophilic substitution) via a pentavalent intermediate state depending on Mg2+. In inorganic chemistry, a phosphate is a salt of phosphoric acid. ... In chemistry, nucleophilic substitution is a class of substitution reaction in which an electron-rich nucleophile attacks a molecule and replaces a group or atom, called the leaving group. ... General Name, Symbol, Number magnesium, Mg, 12 Chemical series alkaline earth metals Group, Period, Block 2, 3, s Appearance silvery white Atomic mass 24. ...


Regulatory GTPases

Regulatory GTPases, also called the GTPase superfamily, are GTPases used for regulation of other biochemical processes. Most prominent among the regulatory GTPases are the G proteins. The GTPase superfamily is a superfamily of switch proteins. ... This article or section does not cite its references or sources. ...


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, GDP-bound form by hydrolysis of the GTP through intrinsic GTPase-activity, effectively switching the GTPase off. This reaction is initiated by GTPase-activating proteins (GAPs), coming from another signal transduction pathway. It can be reverted (switching the GTPase on again) by Guanine nucleotide exchange factors (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. In biology, signal transduction is any process by which a cell converts one kind of signal or stimulus into another. ... Guanosine triphosphate (GTP) is also known as guanosine-5-triphosphate. ... Hydrolysis is a chemical process in which a molecule is split into two parts by the addition of a molecule of water. ...


Switch regulation

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

with kdiss.GDP being the dissociation constant of GDP, and kcat.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 inhibitors (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.

Heterotrimeric G proteins

These G proteins are made from three subunits, with the G domain located on the largest one (the α unit); together with the two smaller subunits (β and γ units), they form a tightly associated protein complex. α and γ unit are associated with the membrane by lipid anchors. Heterotrimeric G proteins act as the specific reaction partners of G protein-coupled receptors. The GTPase is normally inactive. Upon receptor activation, the intracellular receptor domain activates the GTPase, which in turn activates other molecules of the signal transduction chain, either via the α unit or the βγ complex. Among the target molecules of the active GTPase are adenylate cyclase and ion channels. The heterotrimeric G proteins can be classified by sequence homology of the α unit into four families: In lipid anchored proteins, a covalently attached fatty acid such as palmitate or myristate serves to anchor them to the cytoplasmic face of the cell membrane. ... The seven transmembrane α-helix structure of a G protein-coupled receptor. ... Adenylate cyclase Adenylate cyclase (EC 4. ... Another, unrelated ion channeling process is part of ion implantation. ... Two or more structures are said to be homologous if they are alike because of shared ancestry, such as two chromosomes that contain the same genes. ...

  1. Gs family. These G proteins are used in the signal transduction of taste and smell. They always use the activation of adenylate cyclase as the next step in the signal chain. Their function is permanently activated by the cholera toxin, which is the cause of the fatal effects of infection with Vibrio cholerae.
  2. Gi family. The i stands for inhibition of the adenylate cyclase; another effector molecule for this protein family is phospholipase C. Also, Gt and Gg proteins are summarized under this label due to sequence homologies. Gt proteins, aka transducin, is used in the light recognition pathway in retina cells. Gg protein occurs in the taste recognition for bitter. Most Gi protein family members can be inhibited by the pertussis toxin of Bordetella pertussis.
  3. Gq family. These proteins usually have phospholipase C as effector protein.
  4. G12 family. These G proteins can be activated by thromboxan receptors and thrombin receptors. Their effector proteins are unknown.

By combination of different α, β and γ subunits, a great variety (>1000) G proteins can be produced. GDP is not needed for GTP. Adenylate cyclase Adenylate cyclase (EC 4. ... Drawing of Death bringing the cholera, in Le Petit Journal. ... Binomial name Vibrio cholerae Pacini 1854 Vibrio cholerae is a gram negative bacterium with a curved-rod shape that causes cholera in humans. ... Adenylate cyclase Adenylate cyclase (EC 4. ... A phospholipase is an enzyme that converts phospholipids into fatty acids and other lipophilic substances. ... Transducin is the name given to the G-protein alpha-subunits that are naturally expressed in vertebrate retina rods and cones. ... According to Sigma product information Pertussis toxin is released from B. pertussis in an inactive form. ... Malcolm Farmer 10:57, 24 December 2005 (UTC) Category: ... A phospholipase is an enzyme that converts phospholipids into fatty acids and other lipophilic substances. ... There are three known thrombin receptors termed PAR1, PAR3 and PAR4 (PAR for protease-activated receptor). ...


Activation cycle of heterotrimeric G proteins

In the basic state, the Gα-GDP-Gβγ complex and the receptor that can activate it are separately associated with the membrane. On receptor activation, the receptor becomes highly affine for the G protein complex. On binding with the complex, GDP dissociates from the complex; the free complex has a high affinity for GTP. Upon GTP binding, both Gα-GTP and Gβγ separate from both the receptor and from each other. Depending on the lifetime of the active state of the receptor, it can activate more G proteins this way.
Both Gα-GTP and Gβγ can now activate separate effector molecules and activate them, thus sending the signal further down the signal reaction chain. Once the intrinsic GTPase activity of the α unit has hydrolyzed the GTP to GDP, the two parts can reassociate to the original, inactive state. The speed of the hydrolysis reaction works as an internal clock for the length of the signal. In chemistry, electron affinity is the amount of energy absorbed when an electron is added to a neutral isolated gaseous atom to form a gaseous ion with a 1- charge. ...


The Ras GTPase superfamily

These are small monomeric proteins homologous to Ras. They are also called small GTPases. Small GTPases have a molecular weight of about 21 kilo-Dalton and generally serve as molecular switches for a variety of cellular signaling events. According to their primary amino acid sequences and biochemical properties, the Ras superfamily is further divided into five subfamilies: Ras, Rho, Rab, Arf and Ran. In molecular biology, Ras is the name of a protein, the gene that encodes it, and the family and superfamily of proteins to which it belongs. ... In biology, small GTPases are small (20-25 KDa) proteins that bind to guanosine triphosphate GTP. This family of proteins are homologous to Ras GTPases and also called the Ras superfamily GTPases. ... In molecular biology, Ras is the name of a protein, the gene that encodes it, and the family and superfamily of proteins to which it belongs. ... Rab is a member of the Ras superfamily of GTPases. ... ADP Ribosylation Factors (ARFs) are members of the ARF family of GTP-binding proteins of the RAS superfamily. ...


Translation factor family

These GTPases play an important role in initiation, elongation and termination of protein biosynthesis. Translation in the cytoplasm; tRNA carries amino acids which are added to the growing peptide chain in the ribosome. ... Coming from the Latin, initiation implies a beginning. ... This diagram shows the elongations (or angle) of the Earths position from the Sun. ... Termination as a technical term has different meanings. ... An overview of protein synthesis. ...


Translocation factors

See signal recognition particle (SRP). Chromosomal translocation of the 4th and 20th chromosome. ... The signal recognition particle (SRP) is a protein-RNA complex that recognizes and transports specific proteins to the endoplasmic reticulum in eukaryotes and the plasma membrane in prokaryotes. ...

See also : biochemistry - G-protein coupled receptors

 
 

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