Novel Natural Inhibitors of CYP1A2 Identified by in Silico and in Vitro Screening

Inhibition of cytochrome P450 (CYP) is a major cause of herb–drug interactions. The CYP1A2 enzyme plays a major role in the metabolism of drugs in humans. Its broad substrate specificity, as well as its inhibition by a vast array of structurally diverse herbal active ingredients, has indicated the possibility of metabolic herb–drug interactions. Therefore nowadays searching inhibitors for CYP1A2 from herbal medicines are drawing much more attention by biological, chemical and pharmological scientists. In our work, a pharmacophore model as well as the docking technology is proposed to screen inhibitors from herbal ingredients data. Firstly different pharmaphore models were constructed and then validated and modified by 202 herbal ingredients. Secondly the best pharmaphore model was chosen to virtually screen the herbal data (a curated database of 989 herbal compounds). Then the hits (147 herbal compounds) were continued to be filtered by a docking process, and were tested in vitro successively. Finally, five of eighteen candidate compounds (272, 284, 300, 616 and 817) were found to have inhibition of CYP1A2 activity. The model developed in our study is efficient for in silico screening of large herbal databases in the identification of CYP1A2 inhibitors. It will play an important role to prevent the risk of herb–drug interactions at an early stage of the drug development process

Solution structure of the N-terminal dsRBD of Drosophila ADAR and interaction studies with RNA

Adenosine deaminases that act on RNA (ADAR) catalyze adenosine to inosine (A-to-I) editing in double-stranded RNA (dsRNA) substrates. Inosine is read as guanosine by the translation machinery; therefore A-to-I editing events in coding sequences may result in recoding genetic information. Whereas vertebrates have two catalytically active enzymes, namely ADAR1 and ADAR2, Drosophila has a single ADAR protein (dADAR) related to ADAR2. The structural determinants controlling substrate recognition and editing of a specific adenosine within dsRNA substrates are only partially understood. Here, we report the solution structure of the N-terminal dsRNA binding domain (dsRBD) of dADAR and use NMR chemical shift perturbations to identify the protein surface involved in RNA binding. Additionally, we show that Drosophila ADAR edits the R/G site in the mammalian GluR-2 pre-mRNA which is naturally modified by both ADAR1 and ADAR2. We then constructed a model showing how dADAR dsRBD1 binds to the GluR-2 R/G stem-loop. This model revealed that most side chains interacting with the RNA sugar-phosphate backbone need only small displacement to adapt for dsRNA binding and are thus ready to bind to their dsRNA target. It also predicts that dADAR dsRBD1 would bind to dsRNA with less sequence specificity than dsRBDs of ADAR2. Altogether, this study gives new insights into dsRNA substrate recognition by Drosophila ADAR