Herpes simplex virus thymidine kinase Mut2 (HSV-TK Mut2)

Herpes simplex virus thymidine kinase Mut2 (HSV-TK Mut2) is an engineered mutant variant of the viral enzyme from herpes simplex virus type 1 (HSV-1), encoded by the UL23 gene, that catalyzes the transfer of the gamma-phosphate from ATP to thymidine and various nucleoside analogs, producing deoxythymidine monophosphate (dTMP) essential for viral DNA replication via the nucleoside salvage pathway.[1][3][5][6][9] This kinase exhibits broader substrate specificity than human TK1 or TK2, phosphorylating deoxythymidine, deoxycytidine, and antiviral prodrugs like acyclovir and ganciclovir, which are then further phosphorylated by cellular kinases into chain-terminating triphosphates that stall viral DNA synthesis.[3][5][6][7] Structurally, it forms a homodimeric α/β protein with five β-sheets, twelve α-helices per subunit, a conserved P-loop for ATP binding, and a substrate pocket accommodating analogs due to a cavity at the thymine base position 5.[1][3][4] In antiviral therapy, HSV-TK activates drugs selectively in infected cells, enhancing treatment of herpes infections.[5][6] In cancer gene therapy, Mut2 variants improve prodrug affinity (e.g., lower Km for GCV), enabling suicide gene approaches where transduced tumor cells are killed by ganciclovir-induced apoptosis, reducing off-target effects compared to wild-type TK.[5][7] Its nonessential role for viral replication in vitro but critical virulence in vivo neurons makes it ideal for attenuated vaccines and vectors.[6] Challenges include balancing efficacy with resistance and bystander killing in therapy.[5][6]

Other names

HSV-1 thymidine kinase Mut2Herpes simplex virus type 1 thymidine kinase mutant 2UL23 gene product Mut2

Phosphorylation of nucleoside analogs to toxic triphosphates, inhibiting viral DNA polymerase Activation of prodrugs in gene therapy, leading to tumor cell death via DNA synthesis inhibition