GTP-Binding Protein Fragments

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Introduction

GTP-binding proteins constitute a superfamily consisting of more than 100 members, existing in eukaryotes from yeast to human. There are at least five families in the superfamily classified structurally: Rho, Ras, Rab, Ran and Sar1/Arf families. Different family regulates different cell functions as biological timers (biotimers).

Mechanism of action

For GTP-binding proteins, the temporal and spatial determination mechanisms of signal transduction would be important to regulate this type of dynamic cellular functions. The GTP-binding proteins cycle between the GDP-bound inactive and GTP-bound active forms. They receive upstream signals through their regulators and transduce signals to downstream targets while they stay in the GTP-bound form. Thus, GTP-binding proteins serve as timers. There are at least three types of regulators for GTP-binding proteins: GDP/GTP exchange protein (GEP) which stimulates conversion from the GDP-bound form to the GTP-bound form; GDP dissociation inhibitor (GDI) which inhibits this reaction; and GTPase activating protein (GAP) which stimulates conversion from the GTP-bound form to the GDP-bound form. And GDI has been found for the Rho and Rab families. Besides, the Rho family-Rho GDI system plays an important role in spatial determination in the actin cytoskeletal control. Rho GDI is also capable of inhibiting GTP hydrolysis by Rho proteins, blocking both intrinsic and GAP-catalyzed GTPase activity.

Application of GTP-Binding Protein Fragments

There are a lot of cell functions of the GTP-binding protein fragments, such as initiating and terminating specific cell functions, determining the periods of time for the continuation of the specific cell functions. Besides, they play key roles in temporal and spatial determination of specific cell functions:

• The Ras family regulates gene expression at least through the MAP kinase cascade.
• The Ran family regulates nucleocytoplasmic transport and microtubule organization.
• The Rho family regulates cytoskeletal reorganization and gene expression. And the function of the Rho family was first demonstrated in yeast.
• The Rab and Sar1/Arf families regulate vesicle trafficking. Rab proteins exist in all eukaryotic cells and form the largest branch of the GTP-binding protein superfamily.

References

1. Ridley, A. J., & Hall, A. (1992). The small GTP-binding protein rho regulates the assembly of focal adhesions and actin stress fibers in response to growth factors. Cell, 70(3), 389-399.
2. Gingras, A. R., Puzon-McLaughlin, W., Bobkov, A. A., & Ginsberg, M. H. (2016). Structural Basis of Dimeric Rasip1 RA Domain Recognition of the Ras Subfamily of GTP-Binding Proteins. Structure, 24(12), 2152-2162.
3. Pereira-Leal, J. B., & Seabra, M. C. (2001). Evolution of the Rab family of small GTP-binding proteins. Journal of molecular biology, 313(4), 889-901.
4. Klebe, C., Bischoff, F. R., Ponstingl, H., & Wittinghofer, A. (1995). Interaction of the nuclear GTP-binding protein Ran with its regulatory proteins RCC1 and RanGAP1. Biochemistry, 34(2), 639-647.