Small GTPase
Small GTPases are a family of hydrolase enzymes that can bind and hydrolyze guanosine triphosphate (GTP). They are a form of G-proteins found in the cytosol which 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 (GDP). The most well-known members are the Ras GTPases and hence they are sometimes called Ras superfamily 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 (GAPs), while GTP exchange is catalyzed by Guanine nucleotide exchange factors (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 GTP-ases in the inactive state.
Small GTPases regulate a wide variety of processes in the cell, including growth, cellular differentiation, cell movement and lipid vesicle transport.
The Ras superfamily
There are more than a hundred proteins in the Ras superfamily.[1] Based on structure, sequence and function, the Ras superfamily is divided into eight main families, each of which is further divided into subfamilies: Ras, Rho, Rab, Rap, Arf, Ran, Rheb, Rad and Rit. 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 and WASP.
The Ras family is generally responsible for cell proliferation, Rho for cell morphology, Ran for nuclear transport and Rab and Arf for vesicle transport.[2]
See also
References
External links
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| 3.6.1 |
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| 3.6.2 |
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| 3.6.3-4: ATPase |
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| 3.6.5: GTPase |
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Rho family of GTPases: Cdc42 (CDC42, TC10, TCL) • RhoUV (RhoU, RhoV) • Rac (Rac1, 2, 3, RhoG) • RhoBTB (1, 2) • RhoH • Rho (A, B, C) • Rnd (1, 2, 3) • RhoDF (RhoF, RhoD)
other: Ras ( HRAS, KRAS, NRAS) · Rab ( RAB23, RAB27) · Arf ( ARF6, SAR1B, ARL13B, ARL6) · Ran · Rheb · Rap
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B enzm: 1.1/2/3/4/5/6/7/8/10/11/13/14/15-18, 2.1/2/3/4/5/6/7/8, 2.7.10, 2.7.11-12, 3.1/2/3/4/5/6/7, 3.1.3.48, 3.4.21/22/23/24, 4.1/2/3/4/5/6, 5.1/2/3/4/99, 6.1-3/4/5-6
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| Synaptic vesicle |
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SNAP25 · SNAP29
Syntaxin (STX1A, STX1B, STX2, STX3, STX4, STX5, STX6, STX7, STX8, STX10, STX11, STX12, STX16, STX17, STX18, STX19)
Munc-18: STXBP1 · STXBP2 · STXBP3 · STXBP4 · STXBP5 · STXBP6
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Other
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| COPI |
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| COPII |
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| RME/Clathrin |
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| Caveolae |
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| Other/ungrouped |
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Vesicle formation
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Small GTPase
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Other
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see also vesicular transport protein disorders
B memb: cead, trns (1A, 1C, 1F, 2A, 3A1, 3A2-3, 3D), othr
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| MAP |
see MAP kinase pathway
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| Calcium |
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| G protein |
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cAMP: Heterotrimeric G protein (Gs/Gi) • Adenylate cyclase • cAMP • 3',5'-cyclic-AMP phosphodiesterase • Protein kinase A
cGMP: Guanylate cyclase • cGMP • 3',5'-cyclic-GMP phosphodiesterase • Protein kinase G
Beta-gamma complex Gβ (GNB1, GNB2, GNB3, GNB4, GNB5) • Gγ (GNGT1, GNGT2, GNG2, GNG3, GNG4, GNG5, GNG7, GNG8, GNG10, GNG11, GNG12, GNG13, BSCL2)
G protein-coupled receptor kinase • AMP-activated protein kinase
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Monomeric
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| Cyclin |
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| Lipid |
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| Other protein kinase |
Serine/threonine: Casein kinase (1, 2) • eIF-2 kinase (EIF2AK3) • Glycogen synthase kinase (GSK1, GSK2, GSK-3, GSK3A, GSK3B) • IκB kinase (CHUK, IKK2, IKBKG) • Interleukin-1 receptor-associated kinase (IRAK1, IRAK2, IRAK3, IRAK4) • Lim kinase (LIMK1, LIMK2) • p21 activated kinases (PAK1, PAK2, PAK3, PAK4) • Rho-associated protein kinase (ROCK1, ROCK2) • Ribosomal s6 kinase (RPS6KA1)
Tyrosine: ZAP70 • Focal adhesion protein-tyrosine kinase (PTK2, PTK2B) • BTK
both: Dual-specificity kinase
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| Other phosphoprotein phosphatase |
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| Apoptosis |
see apoptosis signaling pathway
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| GTP-binding protein regulators |
see GTP-binding protein regulators
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| Other |
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see also deficiencies of intracellular signaling peptides and proteins
B trdu: iter (nrpl/grfl/cytl/horl), csrc (lgic, enzr, gprc, igsr, intg, nrpr/grfr/cytr), itra (adap, gbpr, mapk), calc, lipd; path (hedp, wntp, tgfp+mapp, notp, jakp, fsap, hipp, tlrp)
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