Small GTPases (), also known as small G-proteins, are a family of

hydrolase Hydrolase is a class of enzyme that commonly perform as biochemical catalysts that use water to break a chemical bond, which typically results in dividing a larger molecule into smaller molecules. Some common examples of hydrolase enzymes are este ...

enzymes that can

bind BIND () is a suite of software for interacting with the Domain Name System (DNS). Its most prominent component, named (pronounced ''name-dee'': , short for ''name daemon''), performs both of the main DNS server roles, acting as an authoritative ...

and

hydrolyze Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysis ...

guanosine triphosphate Guanosine-5'-triphosphate (GTP) is a purine nucleoside triphosphate. It is one of the building blocks needed for the synthesis of RNA during the transcription process. Its structure is similar to that of the guanosine nucleoside, the only d ...

(GTP). They are a type of

G-protein G proteins, also known as guanine nucleotide-binding proteins, are a family of proteins that act as molecular switches inside cells, and are involved in transmitting signals from a variety of stimuli outside a cell to its interior. Their act ...

found in the

cytosol The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells ( intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondri ...

that are homologous to the alpha subunit of heterotrimeric G-proteins, but unlike the alpha subunit of G proteins, a small GTPase can function independently as a hydrolase enzyme to bind to and hydrolyze a guanosine triphosphate (GTP) to form

guanosine diphosphate Guanosine diphosphate, abbreviated GDP, is a nucleoside diphosphate. It is an ester of pyrophosphoric acid with the nucleoside guanosine. GDP consists of a pyrophosphate group, a pentose sugar ribose, and the nucleobase guanine. GDP is the product ...

(GDP). The best-known members are the Ras GTPases and hence they are sometimes called Ras subfamily GTPases. A typical G-protein is active when bound to GTP and inactive when bound to GDP (i.e. when the GTP is hydrolyzed to GDP). The GDP can be then replaced by free GTP. Therefore, a G-protein can be switched on and off. GTP hydrolysis is accelerated by

GTPase activating proteins GTPase-activating proteins or GTPase-accelerating proteins (GAPs) are a family of regulatory proteins whose members can bind to activated G proteins and stimulate their GTPase activity, with the result of terminating the signaling event. GAPs are a ...

(GAPs), while GTP exchange is catalyzed by

guanine nucleotide exchange factors Guanine nucleotide exchange factors (GEFs) are proteins or protein domains that activate monomeric GTPases by stimulating the release of guanosine diphosphate (GDP) to allow binding of guanosine triphosphate (GTP). A variety of unrelated struc ...

(GEFs). Activation of a GEF typically activates its cognate G-protein, while activation of a GAP results in inactivation of the cognate G-protein. Guanosine nucleotide dissociation inhibitors (GDI) maintain small GTPases in the inactive state. Small GTPases regulate a wide variety of processes in the

cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery ...

, including growth, cellular differentiation, cell movement and

lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids includ ...

vesicle Vesicle may refer to: ; In cellular biology or chemistry * Vesicle (biology and chemistry) In cell biology, a vesicle is a structure within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer. Vesicles form nat ...

transport.

The Ras superfamily

There are more than a hundred proteins in the Ras superfamily. Based on structure, sequence and function, the Ras superfamily is divided into five main families, (Ras,

Rho Rho (uppercase Ρ, lowercase ρ or ; el, ρο or el, ρω, label=none) is the 17th letter of the Greek alphabet. In the system of Greek numerals it has a value of 100. It is derived from Phoenician letter res . Its uppercase form uses the sa ...

Ran Ran, RaN and ran may refer to: Arts and entertainment * ''Ran'' (film), a 1985 film directed by Akira Kurosawa * "Ran" (song), a 2013 Japanese song by Luna Sea * '' Ran Online'', a 2004 MMORPG (massively multiplayer online role playing game) * ...

Rab Rab �âːb( dlm, Arba, la, Arba, it, Arbe, german: Arbey) is an island in the northern Dalmatia region in Croatia, located just off the northern Croatian coast in the Adriatic Sea. The island is long, has an area of and 9,328 inhabitants (2 ...

and

Arf ARF may refer to: Organizations * Advertising Research Foundation * Animal Rescue Foundation * Armenian Revolutionary Federation * ASEAN Regional Forum People * Cahit Arf (1910–1997), Turkish mathematician Science, medicine, and mathematics * ...

GTPases). The Ras family itself is further divided into 6 subfamilies:

Ras Ras or RAS may refer to: Arts and media * RAS Records Real Authentic Sound, a reggae record label * Rundfunk Anstalt Südtirol, a south Tyrolese public broadcasting service * Rás 1, an Icelandic radio station * Rás 2, an Icelandic radio stati ...

, Ral,

Rit Rit is a brand of dye A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied i ...

Rap Rapping (also rhyming, spitting, emceeing or MCing) is a musical form of vocal delivery that incorporates "rhyme, rhythmic speech, and street vernacular". It is performed or chanted, usually over a backing beat or musical accompaniment. The ...

, Rheb, and Rad. ''Miro'' is a recent contributor to the superfamily. Each subfamily shares the common core G domain, which provides essential GTPase and nucleotide exchange activity. The surrounding sequence helps determine the functional specificity of the small GTPase, for example the 'Insert Loop', common to the Rho subfamily, specifically contributes to binding to effector proteins such as

IQGAP IQ motif containing GTPase activating protein (IQGAP) is a carrier protein. It is associated with the Rho GTP-binding protein. Genes * IQGAP1 Ras GTPase-activating-like protein IQGAP1 (IQGAP1) also known as p195 is a ubiquitously expressed prote ...

and

WASP A wasp is any insect of the narrow-waisted suborder Apocrita of the order Hymenoptera which is neither a bee nor an ant; this excludes the broad-waisted sawflies (Symphyta), which look somewhat like wasps, but are in a separate suborder. ...

. The Ras family is generally responsible for cell proliferation, Rho for cell morphology, Ran for nuclear transport and Rab and Arf for vesicle transport.

References

External links

* {{Portal bar, Biology, border=no EC 3.6.5 Peripheral membrane proteins

The Ras superfamily

See also

References

External links