Computational Rationale for the Selective Inhibition of the Herpes Simplex Virus Type 1 Uracil-DNA Glycosylase Enzyme

The herpes simplex virus uracil-DNA glycosylase (hsvUNG) enzyme is responsible for the reactivation of the virus from latency and efficient viral replication in nerve tissue. The lack of uracil-DNA glycosylase enzyme in human neurons and the continuous deamination of cytosine create an environment where the presence of viral uracil-DNA glycosylase is a necessity for the proliferation of the virus. A series of 6-(4-alkylanilino)-uracil inhibitors has been developed that selectively and strongly binds to the hsvUNG enzyme while weakly binding to human uracil-DNA glycosylase (hUNG). Here, by using a combination of sequence and structural comparisons between the two enzymes along with free energy of binding computations and principal component analysis of the ligands, we investigate and rationalize the inhibitory effect of the 6-(4-alkylanilino)-uracil series as a function of alkyl chain length on the hsvUNG. The results of these computations corroborate the experimental finding that the inhibitor with an octyl aliphatic chain selectively binds hsvUNG best. More importantly we find that 6-(4-octylanilino)-uracils selective inhibition of hsvUNG over hUNG is due to the combination of the solution preconfigured bent conformation of that specific chain length and the position of HIS92 (absent in hUNG) just outside hsvUNGs hydrophobic gorge lying adjacent to its uracil binding pocket. The similarities between the uracil binding pockets in hsvUNG and hUNG obfuscate an understanding of the preferential inhibition of the virus enzyme. However, the differences in the enzymes shallow hydrophobic grooves adjacent to the binding pockets, such as the gorge we identify here, rationalizes 6-(4-alkylanilino)-uracil with an octyl chain length as an excellent pharmacophore template for hsvUNG inhibitor design.