Herpes simplex virus type 1 DNA polymerase. Mechanism of inhibition by acyclovir triphosphate.
Acyclovir triphosphate (ACVTP) was a substrate for herpes simplex virus type 1 (HSV-1) DNA polymerase and was rapidly incorporated into a synthetic template-primer designed to accept either dGTP or ACVTP followed by dCTP. HSV-1 DNA polymerase was not inactivated by ACVTP, nor was the template-primer with a 3'-terminal acyclovir monophosphate moiety a potent inhibitor. Potent inhibition of HSV-1 DNA polymerase was observed upon binding of the next deoxynucleoside 5'-triphosphate coded by the template subsequent to the incorporation of acyclovir monophosphate into the 3'-end of the primer. The Ki for the dissociation of dCTP (the "next nucleotide") from this dead-end complex was 76 nM. In contrast, the Km for dCTP as a substrate for incorporation into a template-primer containing dGMP in place of acyclovir monophosphate at the 3'-primer terminus was 2.6 microM. The structural requirements for effective binding of the next nucleotide revealed that the order of potency of inhibition of a series of analogs was: dCTP much greater than arabinosyl-CTP greater than 2'-3'-dideoxy-CTP much greater than CTP, dCMP, dCMP + PPi. In the presence of the next required deoxynucleotide (dCTP), high concentrations of dGTP compete with ACVTP for binding and thus retard the formation of the dead-end complex. This results in a first-order loss of enzyme activity indistinguishable from that expected for a mechanism-based inactivator. The reversibility of the dead-end complex was demonstrated by steady-state kinetic analysis, analytical gel filtration, and by rapid gel filtration through Sephadex G-25. Studies indicated that potent, reversible inhibition by ACVTP and the next required deoxynucleoside 5'-triphosphate also occurred when poly(dC)-oligo(dG) or activated calf thymus DNA were used as the template-primer.
Reardon
J E
JE
Experimental Therapy Division, Wellcome Research Laboratories, Research Triangle Park, North Carolina 27709.
Spector
T
T
D000212:Acyclovir / Q000031:analogs & derivatives* / Q000494:pharmacology; D003854:Deoxyribonucleotides / Q000378:metabolism; D006367:HeLa Cells; D019384:Nucleic Acid Synthesis Inhibitors; D018139:Simplexvirus / Q000201:enzymology*; D013379:Substrate Specificity; D013698:Templates, Genetic
D003854:Deoxyribonucleotides; D019384:Nucleic Acid Synthesis Inhibitors; C025114:acyclovir triphosphate; D000212:Acyclovir