Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.1 (protein kinase)
 81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Investigations in numerous laboratories have characterized a salt transport system, present in many animal cell types, which catalyzes the transmembrane transport of NaCl and KCl in a tightly coupled process. The system is inhibited by loop diuretics such as furosemide and bumetanide. This transport system has been designated the loop diuretic-sensitive NaCl/KCl symporter. It has been implicated in transepithelial salt secretion and absorption as well as in cell volume regulation, and it may be defective in patients suffering from essential hypertension. This review serves to evaluate research conducted to date regarding the mechanism, mode of regulation, and physiological significance of the transport system. Ion binding specificities and absolute binding constants for all three naturally occurring ions have been determined in one cell system, the MDCK kidney epithelial cell line. In that same cell line, substrate binding was shown to exhibit apparent cooperativity. although a few reports suggest unidirectional transport of ions via this system under certain conditions, the consensus of reports indicates fully reversible, bidirectional salt transport with the direction of net flux determined by the magnitudes of the gradients of the three transported ions. Growth of cells in media containing a low concentration of K+ (less than 0.25 mM) allows selection of mutants lacking or defective in the symporter. Kinetic analyses with the MDCK cell line have shown that the symporter catalyzes accelerative exchange transport. However, exchange transport of one ion in the absence of one of the other two ionic substrates has not been documented. Comparison with other well-characterized transmembrane transport systems has shown that the characteristics of the NaCl/KCl symporter most resemble those of two-species facilitators (chemiosmotically-coupled symporters) found in prokaryotes and eukaryotes alike. these two-species facilitators consist of a single transmembrane protein and may function by a carrier-type mechanism as originally proposed by Peter Mitchell. A molecular model for the NaCl/KCl symporter is presented and discussed. Activation of symport activity requires ATP and probably occurs by a protein kinase-catalyzed mechanism. In some cell types activation is cyclic AMP dependent. ATP hydrolysis is not stoichiometric with transport. Phosphorylation of an integral membrane protein with an apparent size of 240 000 daltons correlates with activation of transport. It is postulated that this protein is the loop diuretic-sensitive NaCl/KCl symporter.
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PMID:Mechanism, regulation and physiological significance of the loop diuretic-sensitive NaCl/KCl symport system in animal cells. 632 61

Neuronal Cdk5 activator (Nck5a) differs from other cyclin-dependent kinase (Cdk) activators in that its amino acid sequence is only marginally similar to the cyclin consensus sequence. Nevertheless, computer modeling has suggested that Nck5a contains the cyclin-fold motif recently identified in the crystal structure of cyclin A. In the present study, a number of truncation mutants and substitution mutants of the Nck5a were produced and tested for the Cdk5 activation and Cdk5 binding activity. The active domain of Nck5a determined by using the truncation mutants consists of the region spanning residues 150 to 291. The size of Nck5a active domain is essentially the same as that of cyclin A required for Cdk2 activation (Lees, E. M., and Harlow, E. (1993) Mol. Cell. Biol. 13, 1194-1201). The change, or the lack of change, in Cdk5 activation activity observed with a number of substitution mutants may be understood on the basis of structure and function relationship of cyclin A. These results provide support to the previous suggestion (Brown, N. R., Noble, M. E. M., Endicott, J. A., Garman, E. F., Wakatsuki, S., Mitchell, E., Rasmussen, B., Hunt, T., and Johnson, L. N. (1995) Structure 3, 1235-1247) that the activation domain of Nck5a adopts a conformation similar to that of cyclin A. They also provide a partial answer to the question of how Nck5a, a non-cyclin, activates a cyclin-dependent kinase.
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PMID:Cyclin-dependent kinase 5 (Cdk5) activation domain of neuronal Cdk5 activator. Evidence of the existence of cyclin fold in neuronal Cdk5a activator. 913 76

Binding of cyclic nucleotide to or autophosphorylation of cGMP-dependent protein kinase (PKG) activates this kinase, but the molecular mechanism of activation for either process is unknown. Activation of PKG by cGMP binding produces a conformational change in the enzyme (Chu, D.-M., Corbin, J. D., Grimes, K. A., and Francis, S. H. (1997) J. Biol. Chem. 272, 31922-31928; Zhao, J., Trewhella, J., Corbin, J., Francis, S., Mitchell, R., Brushia, R., and Walsh, D. (1997) J. Biol. Chem. 272, 39129-31936). In the present studies, activation of type Ibeta PKG by either autophosphorylation or cGMP-binding alone causes (i) an electronegative charge shift on ion exchange chromatography, (ii) a similar increase ( approximately 3.5 A) in the Stokes radius as determined by gel filtration chromatography, and (iii) a similar decrease in the mobility of the enzyme on native gel electrophoresis. Consistent with these results, cGMP binding increases the rate of phosphoprotein phosphatase-1 catalyzed dephosphorylation of PKG which is autophosphorylated only at Ser-63 (not activated); however, dephosphorylation of PKG that is highly autophosphorylated (activated) is not stimulated by cGMP. The combined results suggest that activation of PKG by either autophosphorylation or cGMP binding alone produces a similar apparent elongation of the enzyme, implying that either process activates the enzyme by a similar molecular mechanism.
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PMID:Activation by autophosphorylation or cGMP binding produces a similar apparent conformational change in cGMP-dependent protein kinase. 960 83