Kinases, nucleotide binding site

Comparison with the nucleotide binding sites in adenylate kinase... 

When the receptor interacts with its associated G protein, the conformation of the guanine-nucleotide-binding site is altered. The subunits then dissociate, and a phosphatidylinositol-specific phospholipase C (PI-PLC) is activated [5]. The subsequent hydrolysis of phosphatidylinositol bisphosphate then produces inositol triphosphate (IP3) and diacylglycerol (DAG), which are known to be secondary messengers. For example, the water soluble IP3 is released into the cell where its ultimate targets are the calcium storage organelles from which Ca2+ is released [3]. The presence of DAG in cells is known to activate the cellular enzyme protein kinase C (PKC) [6, 7], which phosphorylates a number of cellular... 

Affinity Labeling of Catalytic ATP Sites. Residues involved in ATP binding are potentially revealed by the use of affinity labels that are based on ATP s structure. Perhaps the most systematically studied of these compounds is 5 -fluorosulfonylbenzoyladenosine (5 -FSBA) (Figure 3a), which has been reported to label at least six kinases (32-A1). In the case of rabbit muscle pyruvate kinase such work has Indicated the presence of a tyrosine residue within the metal nucleotide binding site and an essential cysteine residue located at or near the free metal binding site (32). A similar reagent, 5 -FSBGuanosine, revealed the presence of two cysteine residues at the catalytic site of this same enzyme, both distinct residues from those modified by 5 -FSBA (33,34). With yeast pyruvate kinase both tyrosine and cysteine residues were modified by 5 -FSBA at the catalytic site ( ), and with porcine cAMP-dependent protein kinase a lysine residue was labeled at the active site (36). 

In fact, kinetic studies of the GTP-dependent avian mitochondrial enzyme indicate two metal-binding sites, one on the polyphosphate group of the bound GTP and one on carboxylate side chains of the protein.252 255 The three-dimensional structure of the ATP-dependent E. coli enzyme reveals a nucleotide binding site similar to the ATP site of adenylate kinase (Fig. 12-30).256 A definite binding site for C02 is also present in the enzyme.257... 

The R proteins, which act as receptors for Avr, and other elicitor proteins, are usually leucine-rich-repeat proteins with a characteristic nucleotide binding site attached (NB-LRR proteins).534,537 Like other cell surface receptors they participate in signaling and utilize both ion channels and Ser/Thr protein kinases.538 The Arabidopsis genome contains 150 sequences that may represent NB-LRR receptors.530... 

Figure 15.33. Structure of Sos, a Guanine-Nucleotide Exchange Factor. Sos (yellow) binds to Ras and opens up its nucleotide-binding site, allowing GDP to escape and GTP to bind. In the GTP-bound form, Ras can bind to and activate other proteins, including protein kinases.

Ras is a membrane-bound GTPase that is required for a variety of signal-transduction pathways. Although it was first thought to be a G protein because of these features, Ras is distinct from the heterotrimeric G proteins a, b, and g (Chapter 16). Ras acts positively to stimulate the cascade of kinase-driven phosphorylation events that culminate in the activation of nuclear transcription factors. Figure 31.10 shows that the active form of Ras has a molecule of GTP bound in the nucleotide binding site, whereas the inactive form of Ras contains a GDP in that site. The intrinsic GTPase activity of Ras therefore converts the active Ras-GTP form into the inactive Ras-GDP moiety. 

The synthesis of the two diastereoisomers of P -l-(2-nitrophenyl)ethyl adenosine S -lri-phosphate (91) has been achieved using resolved (R)- and (5)-l-(2-nilroidienyl)ethanol. The alcohols were converted to (R)- and (5)-l-(2-nitrophenyl)ethyl phosphates by phosphitylation with N,)V-diisopropyl-fi(s-(2-cyanoethyl)phosphoramidite (92) and subsequent oxidation with 3-chlorobenzoic acid. Each of the monophosphates was activated with carbonyidiimidazole and condensed with adenosine diphosphate to give the desired triphosphate. These ATP analogues can be used for the rapid release (by flash photolysis) of ATP in biological systems. The 8-azido-3 -0-anthraniloyl derivatives of 2 -dADP (93) and 2 -dATP (94) have been prepared in seven steps from 8-azido-2 -deoxyadenosine. These compounds are of interest as fluorescent and photoactivatable probes for the nucleotide binding site of kinases and cyclases. In particular, (94) was shown to be a competitive inhibitor of Bordetella pertussis adenylate cyclase and the observed K- (74 pM) was close to tiiat predicted from the K- value of 3 -0-anthraniloyl-2 -dATP. ... 

Stewart, R.G., VanRruggen, R., Ellefson, D.D. and Wolfe, A.J. (1998). TNP-ATP and TNP-ADP as probes of the nucleotide binding site of CheA, the histidine protein kinase in the chemotaxis signal transduction pathway of Escherichia coli. Biochemistry 37,12 269-12 279. 

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