Human leukotriene A4 hydrolase/aminopeptidase (LTA4H) is a zinc metalloenzyme with a dual catalytic activity; conversion of LTA4 into LTB4 and degradation of chemotactic tripeptide Pro-Gly-Pro (PGP). Existing inhibitors, such as SC-57461A, block both catalytic activities of the enzyme, leading to drug failures. Recently, a novel compound, ARM1, was reported to selectively inhibit the hydrolase activity of LTA4H while sparing its aminopeptidase activity. However, the molecular understanding of such preferential inhibitory mechanism remains obscure. The discovery of ARM1 prompted us to further explore its binding theme and provide more insight into the structural and dual mechanistic features of LTA4H protein. To accomplish this, we embarked on wide range of computational tools, including comparative molecular dynamics (MDs) simulations and postdynamic analyses for LTA4H and in complex with ARM1, PGP, ARM1-PGP, and SC-57461A. MD analysis reveals that the binding of ARM1 exhibits a more stable active site and overall stable protein conformation when compared to the nonselective inhibitor SC-57461A. In addition, MM/GBSA-binding free energy calculation also reveals that ARM1 exhibit a lower binding affinity, when compared to the nonselective inhibitor SC-57461A - which is in a great agreement with experimental data. Per residue energy decomposition analysis showed that Phe314, Val367, Tyr378, Trp311, Pro382, and Leu369 are key residues critical for the selective inhibition of the epoxide hydrolase activity of LTA4H by ARM1. Findings from this report will not only provide more understanding into the structural, dynamic, and mechanistic features of LTA4H but would also assist toward the rational design of novel and selective hydrolase inhibitors of LTA4H as anti-inflammatory drugs.
Keywords: ARM1; dual LTA4H hydrolase/aminopeptidase; molecular dynamics; selective inhibition.