Theoretical evaluation and improvement on the potency of the rhodanine-based inhibitors for human serotonin N-acetyltransferase

Human serotonin N-acetyltransferase (hAANAT), included in the melatonin biosynthesis, plays a pivotal role in the regulation of the biological clock and the daily rhythm. In this research, a reliable model of hAANAT was first constructed by the homology modelling method. Then the inhibition mode of two representative rhodanine-based inhibitors was explored by molecular dynamics simulations and energy analyses. The results show that the inhibitor class could share a similar inhibition mechanism in which the carboxyl moiety is positioned in the Ac-CoA binding region while the other end spans the serotonin binding pocket. The interaction between the inhibitor's carboxyl and the enzyme seems to be more important according to the decomposition of binding free energy. Based on the proposed inhibition mode, the inhibitor's improvement was carried out to obtain a more potent compound. The newly designed inhibitor, with the larger binding free energy, exhibits the stronger interaction with the related residues of the enzyme by the added chemical groups. This work will shed light on the inhibition mechanism of the rhodanine-based inhibitors and promote the development of a new drug targeting hAANAT.