View source for Part:BBa K404315

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<h2>Tymidine kinase</h2>
Thymidine kinase (TK) (EC 2.7.1.21) is known to be involved in the salvage pathway of nucleosides to nucleotides (Andrei et al. 2005). Due to its broader spectrum for different substrates, herpes simplex virus thymidine kinase (HSV-TK) is widely used in gene therapy approaches instead of endogenous thymidine kinases (Black et al. 1996). The transgenic introduced HSV-TK monophosphrylates nucleosides or nucleoside analogs such as ganciclovir (GCV) or acyclovir (AVC) followed by further phosphorylation through cellular kinases to nucleoside triphsphosphates. Incorporation of nucleotide analogs such as ganciclovir triphosphate or acyclovir triphosphates leads to DNA chain termination (Reardon 1989) and finally results in cell death. Genetic modifications of the active site represented by a tripeptide motif in thymidine kinase increases the substrate affinity of HSV-TK towards GCV and ACV (Black et al. 1996). Two promising mutant HSV-TKs have been found by large mutagenesis screenings modifying several amino acids and conducting sensitivity assays for ganciclovir and acyclovir (Black et al. 2001). 
SR39
In contrast to the TK30 mutant, the modified thymidine kinase SR39 obtained from a semi-random (SR) mutagenesis screening contains five modifications listed in Table 1 and provides further specificity for nucleoside analogs ganciclovir and acyclovir. <br>
<h2>Mouse guanylate kinase</h2>
Guanylate kinases (GMKs) are involved in the salvage pathway of mono-phosphorylated guanosine (GMP) nucleosides to GDP therefore being essential in nucleotide maturation (Stolworthy & Black 2001). By introducing transgenic thymidine kinases (TKs) into tumor cells, a bottleneck occurs by overexpression of mono-phosphorylated intermediates. To overcome the accumulation of these non-toxic molecules, Willmon, Krabbenhoft, & Black (2006) fused the herpes simplex virus thymidine kinase (HSV-TK) to the guanylate kinase from M. musculus and demonstrated enhanced tumor killing in vitro.<br>


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===Usage and Biology===

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<span class='h3bb'>Sequence and Features</span>
<partinfo>BBa_K404315 SequenceAndFeatures</partinfo>


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===Functional Parameters===
<partinfo>BBa_K404315 parameters</partinfo>
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<h2>References</h2>
Andrei G, Balzarini J, Fiten P "Characterization of herpes simplex virus type 1 thymidine kinase mutants selected under a single round of high-dose brivudin." Journal of virology. 2005;79(9):5863-9.<br>
Black ME, Newcomb TG, Wilson HM, Loeb La. "Creation of drug-specific herpes simplex virus type 1 thymidine kinase mutants for gene therapy." Proceedings of the National Academy of Sciences of the United States of America. 1996;93(8):3525-9<br>
Black ME, Kokoris MS, Sabo P. "Herpes simplex virus-1 thymidine kinase mutants created by semi-random sequence mutagenesis improve prodrug-mediated tumor cell killing." Cancer research. 2001;61(7):3022-6 <br>
Ardiani a, Sanchez-Bonilla M, Black ME " Fusion enzymes containing HSV-1 thymidine kinase mutants and guanylate kinase enhance prodrug sensitivity in vitro and in vivo." Cancer gene therapy. 2010;17(2):86-96<br>
Sekulic, N. et al., 2002. Structural characterization of the closed conformation of mouse guanylate kinase. The Journal of biological chemistry, 277(33), 30236-43. Available at: http://www.ncbi.nlm.nih.gov/pubmed/12036965. <br>
Stolworthy, T.S. & Black, M.E., 2001. The mouse guanylate kinase double mutant E72Q/D103N is a functional adenylate kinase. Protein engineering, 14(11), 903-9. Available at: http://www.ncbi.nlm.nih.gov/pubmed/11742110. <br>
Willmon, C.L., Krabbenhoft, E. & Black, M.E., 2006. A guanylate kinase/HSV-1 thymidine kinase fusion protein enhances prodrug-mediated cell killing. Gene therapy, 13(17), 1309-12. Available at: http://www.ncbi.nlm.nih.gov/pubmed/16810197.<br>