Nucleoside monophosphate kinases structure

Vonrhein et al. 1995] Vonrhein, C., Schlauderer, G.J., Schulz, G.E. Movie of the structural changes during a catalytic cycle of nucleoside monophosphate kinases. Structure 3 (1995) 483-490. 

Yan, H. Tsai, M.-D. Nucleoside monophosphate kinases structure, mechanism, and substrate specificity. Adv. EnzymoL Relat. Areas Mol. Biol., 73, 103-134 (1999)... 

Bucurenci, N. Sakamoto, H. Briozzo, P. Palibroda, N. Serina, L. Sarfati, R.S. Labesse, G. Briand, G. Danchin, A. Barzu, O. Gilles, A.M. CMP kinase from Escherichia coli is structurally related to other nucleoside monophosphate kinases. J. Biol. Chem., 271, 2856-2862 (1996)... 

Briozzo, P. Golinelli-Pimpaneau, B. Gilles, A.M. Gaucher, J.R Burlacu-Miron, S. Sakamoto, H. Janin, J. Barzu, O. Structures of Escherichia coli CMP kinase alone and in complex with CDP a new fold of the nucleoside monophosphate binding domain and insights into cytosine nucleotide specificity. Structure, 6, 1517-1527 (1998)... 

Adenylate kinase performs the essential function of recovering AMP formed by many enzymatic processes and converting it to ADP (Eq. 6-65) which can be reconverted to ATP by oxidative or substrate level phosphorylation. The enzyme is present in all organisms. In vertebrates different isoenzymes function in the cytosol, mitochondrial intermembrane space, and mitochondrial matrix.862 863 A group of other nucleotide and deoxynucleotide kinases convert nucleoside monophosphates into diphosphates.864 865 Some of them, e.g., uridylate kinase are similar in structure and properties to adenylate kinase.866 867 Another member of the adenylate kinase family is phosphoribulokinase, an important photosynthetic enzyme (see Fig. 17-14, step a).868... 

Aciclovir is a member of a group of nucleoside derivatives termed acyclonucleosides, in that there is an incomplete sugar ring. The structural relationship to 2 -deoxyguanosine should be very clear. Aciclovir is converted into its monophosphate by the viral enzyme thymidine kinase - some viruses also possess enzymes that facilitate their replication in the host cell. The viral enzyme turns out to be much more effective than that of the host cell, and conversion is, therefore, mainly in infected cells. The monophosphate is subsequently converted into the triphosphate hy the host cell enzymes. Aciclovir triphosphate inhibits viral DNA polymerase, much more so than it does the host enzyme, and so terminates DNA replication. 

Acyclovir (ACV) is not a true nucleoside, because the guanine residue is attached to an open-chain structure, but it mimics deoxyribose well enough for the compound to be accepted as a substrate by a thymidine kinase specified by certain herpes-type viruses. The normal thymidine kinase in mammalian cells does not recognize ACV as a substrate, however, so only virus-infected cells convert ACV to its monophosphate. Once the first phosphate has been added, the second phosphate is added by cellular guanylate kinase several other cellular kinases can add the third phosphate. The triphosphate is a more potent inhibitor of the viral DNA polymerases than of cellular DNA polymerases and also inactivates the former but not the latter. The net result is that ACV has been an effective treatment of, and prophylaxis for, genital herpes. Also it can result in dramatic relief of pain associated with shingles caused by reactivation of latent varicella-zoster virus, and has been successful in many patients with herpes encephalitis. 

THYMIDINE KINASE (TK) An enzyme involved in the utilization of the nucleoside thymidine (which ultimately becomes part of the structure of DNA) catalyzes the phosphorylation of thymidine to thymidine monophosphate mutants that lack TK are resistant to the toxic effects of several thymidine analogues, including bromodeoxy-uridine and trifluorothymidine selection of these drug-resistant mutants provides the basis of several... 

An interesting alternative to amines derived from amino acids is based on the 4-chlorobutyl system as reflected in structure 66. After reduction and loss of the nitrofuryl group, cyclization of the butyl group delivers the active nucleotide, as shown by the preservation of activity in cells deficient in the kinase that generates FdUMP [143] or AraC monophosphate from the corresponding nucleosides [144]. 

Bios5mthetic pathways of naturally occurring cytokinins are illustrated in Fig. 29.5. The first step of cytokinin biosynthesis is the formation of A -(A -isopentenyl) adenine nucleotides catalyzed by adenylate isopentenyltransferase (EC 2.5.1.27). In higher plants, A -(A -isopentenyl)adenine riboside 5 -triphosphate or A -(A -isopentenyl)adenine riboside 5 -diphosphate are formed preferentially. In Arabidopsis, A -(A -isopentenyl)adenine nucleotides are converted into fraws-zeatin nucleotides by cytochrome P450 monooxygenases. Bioactive cytokinins are base forms. Cytokinin nucleotides are converted to nucleobases by 5 -nucleotidase and nucleosidase as shown in the conventional purine nucleotide catabolism pathway. However, a novel enzyme, cytokinin nucleoside 5 -monophosphate phosphoribo-hydrolase, named LOG, has recently been identified. Therefore, it is likely that at least two pathways convert inactive nucleotide forms of cytokinin to the active freebase forms that occur in plants [27, 42]. The reverse reactions, the conversion of the active to inactive structures, seem to be catalyzed by adenine phosphoiibosyl-transferase [43] and/or adenosine kinase [44]. In addition, biosynthesis of c/s-zeatin from tRNAs in plants has been demonstrated using Arabidopsis mutants with defective tRNA isopentenyltransferases [45]. 

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