GTP-binding protein

(noun)

a protein which binds GTP and catalyzes its conversion to GDP

Related Terms

Examples of GTP-binding protein in the following topics:

  • Signaling in Yeast

    • When mating factor binds to cell-surface receptors in other yeast cells that are nearby, they stop their normal growth cycles and initiate a cell signaling cascade that includes protein kinases and GTP-binding proteins that are similar to G-proteins.
    • Because yeasts contain many of the same classes of signaling proteins as humans, these organisms are ideal for studying signaling cascades.

  • Plasma Membrane Hormone Receptors

    • When a hormone binds to its membrane receptor, a G protein that is associated with the receptor is activated.
    • G proteins are proteins separate from receptors that are found in the cell membrane.
    • When a hormone binds to the receptor, the G protein is activated by binding guanosine triphosphate, or GTP, in place of GDP.
    • After binding, GTP is hydrolyzed by the G protein into GDP and becomes inactive .
    • The binding of a hormone at a single receptor causes the activation of many G-proteins, which activates adenylyl cyclase.

  • The Initiation Complex and Translation Rate

    • Like transcription, translation is controlled by proteins that bind and initiate the process.
    • With GTP bound to it, eIF-2 protein binds to the small 40S ribosomal subunit.
    • The eIF5-GTP allows the 60S large ribosomal subunit to bind.
    • If eIF-2 is phosphorylated, it undergoes a conformational change and cannot bind to GTP.
    • When eIF-2 remains unphosphorylated, it binds the 40S ribosomal subunit and actively translates the protein .

  • Direct Gene Activation and the Second-Messenger System

    • Hormone binding to the nuclear receptor results in dissociation of the co-repressor and the recruitment of co-activator proteins.
    • Most hormone receptors are G protein-coupled receptors.
    • Upon hormone binding, the receptor undergoes a conformational change and exposes a binding site for a G-protein.
    • Upon binding to the receptor, it releases a GTP molecule, at which point the alpha sub-unit of the G-protein breaks free from the beta and gamma sub-units and is able to move along the inner membrane until it contacts another membrane-bound protein: the primary effector. 
    • G-protein is activated and produces an effector. 3.

  • Types of Receptors

    • G-protein-linked receptors bind a ligand and activate a membrane protein called a G-protein.
    • Once the G-protein binds to the receptor, the resultant shape change activates the G-protein, which releases GDP and picks up GTP.
    • Later, the GTP on the active α subunit of the G-protein is hydrolyzed to GDP and the β subunit is deactivated.
    • When a signaling molecule binds to a G-protein-coupled receptor in the plasma membrane, a GDP molecule associated with the α subunit is exchanged for GTP.
    • Hydrolysis of GTP to GDP terminates the signal.

  • The Mechanism of Protein Synthesis

    • Protein synthesis begins with the formation of a pre-initiation complex.
    • In eukaryotes, a pre-initiation complex forms when an initiation factor called eIF2 (eukaryotic initiation factor 2) binds GTP, and the GTP-eIF2 recruits the eukaryotic initiator tRNA to the 40s small ribosomal subunit.
    • Several other eIFs, specifically eIF1, eIF3, and eIF4, act as cap-binding proteins and assist the recruitment of the pre-initiation complex to the 5' cap.
    • Poly (A)-Binding Protein (PAB) binds both the poly (A) tail of the mRNA and the complex of proteins at the cap and also assists in the process.
    • After this, eIF2-GDP is released from the complex, and eIF5-GTP binds.

  • Activation of Starvation by Survival Genes

    • In Escherichia coli, (p)ppGpp production is mediated by the ribosomal protein L11 and the ribosome-associated protein RelA with the A-site bound deacylated tRNA being the ultimate inducer.
    • RelA converts GTP and ATP into pppGpp by adding the pyrophosphate from ATP onto the 3' carbon of the ribose in GTP, releasing AMP . pppGpp is converted to ppGpp by the gpp gene product, releasing Pi . ppGpp is converted to GDP by the spoT gene product, releasing pyrophosphate ( PPi ).
    • GDP is converted to GTP by the ndk gene product.
    • Some of these proteins activate synthetically, hydrolytically, or both (Rel) .
    • (p)ppGpp is thought to bind RNA polymerase and alter the transcriptional profile, decreasing the synthesis of translational machinery (such as rRNA and tRNA), and increasing the transcription of biosynthetic genes.

  • The Stringent Response

    • In Escherichia coli, (p)ppGpp production is mediated by the ribosomal protein L11.
    • The ribosome-associated protein RelA with the A-site bound deacylated tRNA is the ultimate inducer.
    • GDP is converted to GTP by the ndk gene product.
    • Translational GTP involved in protein biosynthesis are also affected by ppGpp, with Initiation Factor 2 (IF2) being the main target.
    • Chemical reaction catalyzed by RelA: $ATP + GTP \rightarrow AMP + pppGpp$

  • Citric Acid Cycle

    • CoA binds the succinyl group to form succinyl CoA.
    • This form produces GTP.
    • GTP is energetically equivalent to ATP; however, its use is more restricted.
    • In particular, protein synthesis primarily uses GTP.
    • One GTP or ATP is also made in each cycle.

  • Fts Proteins and Cell Division

    • This is a prokaryotic homologue to the eukaryotic protein tubulin.
    • FtsZ was the first protein of the prokaryotic cytoskeleton to be identified.
    • During cell division, FtsZ is the first protein to move to the division site, and is essential for recruiting other proteins that produce a new cell wall between the dividing cells.
    • FtsZ has the ability to bind to GTP, and also exhibits a GTPase domain that allows it to hydrolyze GTP to GDP and a phosphate group.
    • The GTP hydrolyzing activity of the protein is not essential to the formation of filaments or division.