scholarly journals Current Topics in Heterotrimeric GTP-binding Proteins. Regulation of G proteins by receptors.

1994 ◽  
Vol 103 (6) ◽  
pp. 273-284 ◽  
Author(s):  
Hitoshi KUROSE ◽  
Taku NAGAO
Keyword(s):  
G Proteins ◽  
Binding Proteins ◽  
Gtp Binding Proteins ◽  
Gtp Binding

scholarly journals Characterization of GTP-binding proteins in Golgi-associated membrane vesicles from rat adipocytes

1992 ◽  
Vol 283 (3) ◽  
pp. 795-801 ◽  
Author(s):  
A Schürmann ◽  
W Rosenthal ◽  
G Schultz ◽  
H G Joost
Keyword(s):  
G Proteins ◽  
Glucose Transport ◽  
Subcellular Distribution ◽  
Sucrose Gradient ◽  
Binding Proteins ◽  
Glucose Transporters ◽  
Beta Subunits ◽  
Transport Activity ◽  
Gtp Binding Proteins ◽  
Gtp Binding

We have previously reported that guanine nucleotides inhibit glucose transport activity reconstituted from adipocyte membrane fractions. In order to further investigate the hypothetical involvement of guanine-nucleotide-binding proteins (GTP-binding proteins) in the regulation of insulin-sensitive glucose transport activity, we studied their subcellular distribution in adipocytes treated or not with insulin. Adipocytes were homogenized and fractionated to yield plasma membranes (PM) and a Golgi-enriched fraction of intracellular membranes (low-density microsomes, LDM). In these membrane fractions, total guanosine 5′-[gamma-[35S]thio]triphosphate ([35S]GTP[S]) binding, alpha- and beta-subunits of heterotrimeric G-proteins, proto-oncogenes Ha-ras and K-ras, and 23-28 kDa GTP-binding proteins were assayed. The levels of alpha s and alpha i (the alpha-subunits of Gs and Gi) were approx. 8-fold lower in LDM than in PM; beta-subunits, Ha-ras and K-ras were not detectable in LDM. Total GTP[S]-binding sites and 23-28 kDa GTP-binding proteins were present in LDM in approximately the same concentrations as in PM. Insulin gave rise to the characteristic translocation of glucose transporters, but failed to alter the subcellular distribution of any of the GTP-binding proteins. Fractionation of the LDM on a discontinuous sucrose gradient revealed that alpha s and alpha i, as detected with antiserum against a common peptide sequence (alpha common), and the bulk of the 23-28 kDa G-proteins sedimented at different sucrose densities. None of the GTP-binding proteins co-sedimented with glucose transporters. Furthermore, the inhibitory effect of GTP[S] on the reconstituted transport activity was lost in the peak fractions of glucose transporters partially purified on the sucrose gradient. These data indicate that LDM from adipocytes contain several GTP-binding proteins in discrete vesicle populations. However, the intracellular GTP-binding proteins are not tightly associated with the vesicles containing the glucose transporter.

Overview of G Proteins (GTP-Binding Proteins) in Eukaryotes

2014 ◽  
pp. 1-7
Author(s):  
Girdhar K. Pandey ◽  
Manisha Sharma ◽  
Amita Pandey ◽  
Thiruvenkadam Shanmugam
Keyword(s):  
G Proteins ◽  
Binding Proteins ◽  
Gtp Binding Proteins ◽  
Gtp Binding

Small GTP-Binding Proteins

2001 ◽  
Vol 81 (1) ◽  
pp. 153-208 ◽  
Author(s):  
Yoshimi Takai ◽  
Takuya Sasaki ◽  
Takashi Matozaki
Keyword(s):  
Gene Expression ◽  
G Proteins ◽  
Binding Proteins ◽  
Nucleocytoplasmic Transport ◽  
Specific Cell ◽  
Microtubule Organization ◽  
Gtp Binding Proteins ◽  
Cell Functions ◽  
Gtp Binding ◽  
Small G Proteins

Small GTP-binding proteins (G proteins) exist in eukaryotes from yeast to human and constitute a superfamily consisting of more than 100 members. This superfamily is structurally classified into at least five families: the Ras, Rho, Rab, Sar1/Arf, and Ran families. They regulate a wide variety of cell functions as biological timers (biotimers) that initiate and terminate specific cell functions and determine the periods of time for the continuation of the specific cell functions. They furthermore play key roles in not only temporal but also spatial determination of specific cell functions. The Ras family regulates gene expression, the Rho family regulates cytoskeletal reorganization and gene expression, the Rab and Sar1/Arf families regulate vesicle trafficking, and the Ran family regulates nucleocytoplasmic transport and microtubule organization. Many upstream regulators and downstream effectors of small G proteins have been isolated, and their modes of activation and action have gradually been elucidated. Cascades and cross-talks of small G proteins have also been clarified. In this review, functions of small G proteins and their modes of activation and action are described.

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