Article

Small GTP-binding proteins. Physiol Rev

Department of Molecular Biology, Osaka University Graduate School of Medicine/Faculty of Medicine, Suita, Japan.
Physiological Reviews (Impact Factor: 29.04). 02/2001; 81(1):153-208.
Source: PubMed

ABSTRACT 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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    • "It is challenging to explain how these very similar effector-binding domains coordinate the different functions of Ras and Rap proteins, which are presumably mediated by different effector molecules. The ability of these small GTPases to signal requires that the GTP-bound state engage specific downstream effectors, interactions that are geographically limited to the cytosolic surface of cellular membranes (Takai et al., 2001). GTPases are targeted to membranes as a result of the post-translational modification process. "
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