Nucleotide-binding proteins

Figure 1. Simplified schematic of receptor-mediated signal transduction in neutrophils. Binding of ligand to the receptor activates a guanine-nucleotide-binding protein (G protein), which then stimulates phospholipase C. Phosphatidylinositol 4,5-bis-phosphate is cleaved to produce diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3). DAG stimulates protein kinase C. IP3 causes the release of Ca from intracellular stores, which results in an increase in the cytosolic Ca concentration. This increase in Ca may stimulate protein kinase C, calmodulin-dependent protein kinases, and phospholipase A2. Protein phosphorylation events are thought to be important in stimulating degranulation and oxidant production. In addition, ionic fluxes occur across the plasma membrane. It is possible that phospholipase A2 and ionic channels may be governed by G protein interactions. ...

G-proteins are trimeric, signal-transducing, guanine nucleotide-binding proteins. They constitute the first step in transducing the agonist-induced activation of a G-protein-coupled receptor (see Chapter 2) to a cellular response. 

Other oncogenes code for proteins that bind guanine nucleotides, and others code for nuclear proteins. The guanine nucleotide-binding proteins, the so-called G proteins, affect several key reactions. Some G proteins are stimulatory, whereas others are inhibitory. For example, they link hormone receptors to adenylate cyclase, they translocate... 

Figure 2.5. The synapse. GPCR = guanine nucleotide-binding protein-coupled receptor, LGICR = ligand-gated ion channel receptor, SB = synaptic bouton, T = neurotransmitter, YOC = voltage-operated ion channel protein, YOCC = voltage-operated calcium channel protein, Ast = astrocyte, AA = axoaxonal synapse, ASD = axosomatic or axodendritic synapse. GPCR 1 = receptor protein, 2 = G-protein, 3 = enzyme, 4 = ion channel protein.

McKenzie FR, Milligan G. Delta-opioid-receptor-mediated inhibition of adenylyl cyclase is transduced specifically by the guanine-nucleotide-binding protein Gi2. Biochem J 1990 267 391-398... 

Increases gastric acidity by preventing the action of inhibitory guanine nucleotide-binding protein (G protein) on adenylate cyclase... 

G. lambha—Giardia lambha G protein—guanine nucleotide-binding protein GABA—y-aminobutyric ac ... 

Cockcroft, S., Stutchfield, J. (1989). ATP stimulates secretion in human neutrophils and HL60 cells via a pertussis toxin-sensitive guanine nucleotide-binding protein coupled to phospholipase C. FEBS Lett. 245,25-9. 

Fig. 3. Three-dimensional structures of three examples of superstructures formed by sequence repeats a linear rod (the spectrin a-chain dimer [PDB 2spc]), a superhelix of repeats (armadillo repeats of importin a-subunit [PDB lbk5]), and a closed /3-propeller (WD40 repeats from a fragment of the /3-subunit of the guanine nucleotide binding protein 1 [PDB lgg2 chain B]).

Maier, T., Jacobi, A., Sauter, M. and Bock, A. (1993) The product of the hypB gene, which is required for nickel incorporation into hydrogenases, is a novel guanine nucleotide-binding protein./. Bacterial., 175, 630-5. 

---