Guanosine nucleotide-binding proteins

Salts of the tetrafluoroaluminate (TFA) anion have been known for many years. Yet aqueous routes to pure materials have not been established despite the substantial amount of literature available on the subject. The present review will discuss the various synthetic methods that have been employed and will demonstrate a revised method for preparing pure TFA salts. These materials are important because TFA is able to stimulate various guanosine nucleotide-binding proteins (G-proteins) and inhibit P-type ATPases by serving as a nonhydrolyzing phosphate mimic. Additionally, various TFA salts serve as precursors to aluminum trifluoride, which is used as a catalyst for chlorofluorocarbon isomerizations and fluorinations. 

G-proteins or guanosine-nucleotide-binding proteins are proteins involved in a diverse range of cellular processes such as signal transduction, vesicular transport, proliferation, differentiation, cell cycle, or nuclear import. G-proteins can be divided in two main classes the heterotrimeric G-proteins (formed by three... 

M FIGURE 3-5 Various graphic representations of the structure of Ras, a monomeric guanine nucleotide-binding protein. The inactive, guanosine diphosphate (GDP)-bound form is shown in all four panels, with GDP always depicted in blue spacefill, (a) The C backbone trace demonstrates how the polypeptide is packed into the smallest possible volume. 

Neubig, R.R., and Sklar, L.A. (1993). Subsecond modulation of formyl peptide-bnked guanine nucleotide-binding proteins by guanosine 5 -0-(3-thio)tiiphos-phate in permeabiUzed neutrophils. Mol. Pharm. 43, 734-740. 

H-ras proteins, the products of the ras onco- and protooncogenes, are guanine nucleotide binding proteins, which act as molecular switch. In the active state, liras proteins are bound to guanosine triphosphate (GTP), and in order to switch to the inactive state, the y-phosphate of the nucleotide has to be hydrolyzed. In the oncogenic mutation, this reaction is suppressed. Understanding this reaction is very important to overcome human cancer, because H-ras proteins frequently mutate to be activated in a variety of human cancer cells [1]. 

Lorenzen, A., Fuss, M., Vogt, H., and Schwabe, U. (1993) Measurement of guanine nucleotide-binding protein activation by A1 adenosine receptor agonists in bovine brain membranes stimulation of guanosine-5 -0-(3-P S]thio)triphosphate binding. Mol. Pharmacol. 44, 115-123. 

The most common second messenger activated by protein/peptide hormones and catecholamines is cyclic adenosine monophosphate (cAMP). The pathway by which cAMP is formed and alters cellular function is illustrated in Figure 10.1. The process begins when the hormone binds to its receptor. These receptors are quite large and span the plasma membrane. On the cytoplasmic surface of the membrane, the receptor is associated with a G protein that serves as the transducer molecule. In other words, the G protein acts as an intermediary between the receptor and the second messengers that will alter cellular activity. These proteins are referred to as G proteins because they bind with guanosine nucleotides. In an unstimulated cell, the inactive G protein binds guanosine diphosphate (GDP). When the hormone... 

The Ras superfamily of GTP-binding proteins is composed of several subfamilies [7] which all contain the Ras-like domain of approximately 160 amino acids and 5 consensus sequences. Two of these highly conserved motifs are responsible for specific recognition of the guanosine nucleotide, and three are necessary for binding of the phosphate groups and complexation of a Mg++ ion, which is found in all Ras-like proteins. 

G-proteins are so called because they bind a guanosine nucleotide, either GTP or GDP. Their transduction mechanism involves the production of a second messenger such as 3 5 cAMP, 3 5 cyclic GMP (cGMP) or IP3 and diacylglycerol (DAG), derived from AMP, GMP and phosphatidyl inositol-3,5bisphosphate respectively (Figure 4.15). It is the second messenger that initiates the downstream amplification process phase of transduction. 

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