WordNet

any of a large group of nitrogenous organic compounds that are essential constituents of living cells; consist of polymers of amino acids; essential in the diet of animals for growth and for repair of tissues; can be obtained from meat and eggs and milk and legumes; "a diet high in protein"
the 18th letter of the Roman alphabet (同)r
ancient Egyptian sun god with the head of a hawk; a universal creator; he merged with the god Amen as Amen-Ra to become the king of the gods (同)Re

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蛋白(たんばく)質
resistance / 17歳以下父兄同伴映画の表示 / rook
radiumの化学記号

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/09/17 20:25:08」(JST)

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The Rab family of proteins is a member of the Ras superfamily of monomeric G proteins.^[1] Approximately 70 types of Rabs have now been identified in humans. Rab GTPases regulate many steps of membrane traffic, including vesicle formation, vesicle movement along actin and tubulin networks, and membrane fusion. These processes make up the route through which cell surface proteins are trafficked from the Golgi to the plasma membrane and are recycled. Surface protein recycling returns proteins to the surface whose function involves carrying another protein or substance inside the cell, such as the transferrin receptor, or serves as a means of regulating the number of a certain type of protein molecules on the surface.

Function

Rab proteins are peripheral membrane proteins, anchored to a membrane via a lipid group covalently linked to an amino acid. Specifically, Rabs are anchored via prenyl groups on two cysteines in the C-terminus. Rab escort proteins (REPs) deliver newly synthesized and prenylated Rab to its destination membrane by binding the hydrophobic, insoluble prenyl groups and carrying Rab through the cytoplasm. The lipid prenyl groups can then insert into the membrane, anchoring Rab at the cytoplasmic face of a vesicle or the plasma membrane. Because Rab proteins are anchored to the membrane through a flexible C-terminal region, they can be thought of as a 'balloon on a string'.

Like other GTPases, Rabs switch between two conformations, an inactive form bound to GDP (guanosine diphosphate), and an active form bound to GTP (guanosine triphosphate). A GDP/GTP exchange factor (GEF) catalyzes the conversion from GDP-bound to GTP-bound form, thereby activating the Rab. The inherent GTP hydrolysis of Rabs can be enhanced by a GTPase-activating protein (GAP) leading to Rab inactivation. REPs carry only the GDP-bound form of Rab, and Rab effectors, proteins with which Rab interacts and through which it functions, only bind the GTP-bound form of Rab. Rab effectors are very heterogeneous, and each Rab isoform has many effectors through which it carries out multiple functions.

After membrane fusion, Rab is recycled back to its membrane of origin. A GDP dissociation inhibitor (GDI) binds the prenyl groups of the inactive, GDP-bound form of Rab, inhibits the exchange of GDP for GTP (which would reactivate the Rab) and delivers Rab to its original membrane.

Clinical significance

Defects in protein prenylation can cause pathologies such as choroideremia.

Types of Rab proteins

There are approximately 70 different Rabs that have been identified in humans thus far. They are mostly involved in vesicle trafficking. Their complexity can be understood if thought of as address labels for vesicle trafficking, defining the identity and routing of vesicles.

Name	Subcellular location
RAB1 (YPT1)	ER, golgi complex
RAB2	ER, cis-golgi network
RAB3A	secretory and synaptic vesicles
RAB4	early endosomes
RAB5A	clathrin-coated vesicles, plasma membranes
RAB5C	early endosomes
RAB6	medial- and trans-golgi network
RAB7	late endosomes
RAB8	basolateral secretory vesicles
RAB9	late endosome, trans-golgi network
RAB11	recycling endosomes
RAB18	lipid droplets, golgi, endoplasmic reticulum
RAB39a	binds Caspase-1 in inflammasome
SEC4	secretory vesicles

Other Rab proteins

RAB6
RAB13
RAB23
RAB27

References

^ Stenmark H, Olkkonen VM (2001). "The Rab GTPase family". Genome Biol. 2 (5): REVIEWS3007. doi:10.1186/gb-2001-2-5-reviews3007. PMC 138937. PMID 11387043.

External links

rab G-Proteins at the US National Library of Medicine Medical Subject Headings (MeSH)

UpToDate Contents

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English Journal

Endocytic Rabs in membrane trafficking and signaling.

Numrich J, Ungermann C.AbstractAbstract The endolysosomal system controls the trafficking of proteins between the plasma membrane and the degradative environment of the lysosome. The early endosomal Rab5 and the late endosomal Rab7 GTPases have a key role in the transport along the endocytic pathway by recruiting tethering factors such as the hexameric CORVET and HOPS complexes that promote membrane fusion. Both Rabs are also involved in signaling at endosomal membranes and linked to amino acid sensing and autophagy, indicating that their role in trafficking may be connected to signal transduction and adaptation during cell stress. Here, we will summarize the current knowledge on the role of both Rab GTPases on both processes and discuss the possible crosstalk between them.
Biological chemistry.Biol Chem.2014 Mar 1;395(3):327-33. doi: 10.1515/hsz-2013-0258.
Abstract The endolysosomal system controls the trafficking of proteins between the plasma membrane and the degradative environment of the lysosome. The early endosomal Rab5 and the late endosomal Rab7 GTPases have a key role in the transport along the endocytic pathway by recruiting tethering factor
PMID 24158421

Regulation of autophagy by the Rab GTPase network.

Ao X1, Zou L2, Wu Y2.Author information 1The Battalion 5 of Cadet Brigade, PLA, Third Military Medical University, Chongqing, China.2Institute of Immunology, PLA, Third Military Medical University, Chongqing, China.AbstractAutophagy (macroautophagy) is a highly conserved intracellular and lysosome-dependent degradation process in which autophagic substrates are enclosed and degraded by a double-membrane vesicular structure in a continuous and dynamic vesicle transport process. The Rab protein is a small GTPase that belongs to the Ras-like GTPase superfamily and regulates the vesicle traffic process. Numerous Rab proteins have been shown to be involved in various stages of autophagy. Rab1, Rab5, Rab7, Rab9A, Rab11, Rab23, Rab32, and Rab33B participate in autophagosome formation, whereas Rab9 is required in non-canonical autophagy. Rab7, Rab8B, and Rab24 have a key role in autophagosome maturation. Rab8A and Rab25 are also involved in autophagy, but their role is unknown. Here, we summarize new findings regarding the involvement of Rabs in autophagy and provide insights regarding future research on the mechanisms of autophagy regulation.
Cell death and differentiation.Cell Death Differ.2014 Mar;21(3):348-58. doi: 10.1038/cdd.2013.187. Epub 2014 Jan 17.
Autophagy (macroautophagy) is a highly conserved intracellular and lysosome-dependent degradation process in which autophagic substrates are enclosed and degraded by a double-membrane vesicular structure in a continuous and dynamic vesicle transport process. The Rab protein is a small GTPase that be
PMID 24440914

Placental gene expression patterns of endoglin (CD105) in intrauterine growth restriction.

Szentpéteri I, Rab A, Kornya L, Kovács P, Brubel R, Joó JG.Author information Praxis für Gynäkologie und Geburtshilfe und allgemeine Medizin , Wehingen, Baden-Württemberg , Germany .AbstractAbstract Objective: In this study, we describe placental gene expression patterns of endoglin in pregnancies with intrauterine growth restriction (IUGR) compared to normal pregnancies. Methods: Placental samples were obtained from 101 pregnancies with IUGR using 140 normal pregnancy cases as control. Gene expression patterns and protein levels of the endoglin were compared between the two groups. For the gene expression analysis real-time PCR was applied, while for the estimation of placental protein level we performed Western analysis. Results: The placental endoglin gene was significantly overexpressed in the IUGR group versus the control group (Ln2(α): 1.69). The placental endoglin protein level proved to be significantly higher in case of IUGR (endoglin/β-actin ratio: 13.8 ± 2.3) versus the control cases (5.3 ± 1.1). The placental gene expression as well as the protein levels of endoglin showed no significant difference between female and male newborns. Concerning the placental gene expression and protein level, no significant difference was justified between the more (0-5 percentile) and less (5-10 percentile) severe cases of IUGR. Conclusion: Increased placental gene expression of endoglin may result in vascular dysfunction leading to chronic fetal hypoxia, which may induce VEGF-A to stimulate angiogenesis. This can be explained as feed back response to restore fetal placental circulation.
The journal of maternal-fetal & neonatal medicine : the official journal of the European Association of Perinatal Medicine, the Federation of Asia and Oceania Perinatal Societies, the International Society of Perinatal Obstetricians.J Matern Fetal Neonatal Med.2014 Mar;27(4):350-4. doi: 10.3109/14767058.2013.818125. Epub 2013 Aug 27.
Abstract Objective: In this study, we describe placental gene expression patterns of endoglin in pregnancies with intrauterine growth restriction (IUGR) compared to normal pregnancies. Methods: Placental samples were obtained from 101 pregnancies with IUGR using 140 normal pregnancy cases as control
PMID 23808956