Site-directed mutagenesis clarifies the substrate position within the three-dimensional model of the active site of herpes simplex virus type-1 thymidine kinase.
Site-directed mutagenesis was used to experimentally verify the 3D model of the active site of herpes simplex virus type-1 thymidine kinase (HSV 1 TK) obtained by homology modelling. For this purpose, D215 and K317 were replaced by R and G, respectively, at homologous positions in the aciclovir-insensitive bovine herpes virus type-1 thymidine kinase (BHV 1 TK). Wild-type and mutated enzymes were expressed in Escherichia coli using a gene fusion vector and purified to homogeneity. While both mutants had the same Km value for thymidine as the recombinant wild-type enzyme (0.2 microM), Vmax was decreased to 20-25% of the original wild-type value. The recombinant wild-type enzyme was inhibited by the substrate analogue aciclovir with a Ki of 146 microM. Both mutants were able to phosphorylate aciclovir to about the same extent as the wild-type enzyme. These findings suggest that neither D215 nor K317 are directly involved in substrate binding. Therefore, a rearrangement of the 3D model is suggested, concerning the assignment of the substrate-binding site and co-substrate-binding site at the right and left side of the phosphate-binding loop, respectively.
Department of Pharmacy, ETH Zürich, Switzerland.
M
M
Michael
J
J
Fetzer
G
G
Folkers
D001483:Base Sequence; D001665:Binding Sites; D004795:Enzyme Stability; D018259:Herpesvirus 1, Human / Q000201:enzymology* / Q000235:genetics; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009838:Oligodeoxyribonucleotides; D010766:Phosphorylation; D013379:Substrate Specificity; D013936:Thymidine / Q000378:metabolism; D013937:Thymidine Kinase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
D009838:Oligodeoxyribonucleotides; D013937:Thymidine Kinase; D013936:Thymidine