Decoding the <i>in-silico</i> structure of isopentenyl Diphosphate Delta-Isomerase protein from <i>Cassia angustifolia</i> Vahl

Senna (<i>Cassia angustifolia</i> Vahl.) is an important medicinal plant used in traditional and modern systems medicine to manage constipation. While various treatment strategies exist, there is growing interest in utilizing traditional herbal medicines like Indian Senna as a natural alternative. Though Isopentenyl Diphosphate Delta-Isomerase (IDI) has been proven to be one of the key enzymes in the sennoside biosynthesis pathway, characterization of it remains largely unexplored. This study aims to bridge the knowledge gap by investigating IDI, an important enzyme involved in sennoside biosynthesis in plants. The study retrieved the coding DNA sequence (CDS) of IDI from Senna transcriptome and successfully cloned and sequenced the gene. Physicochemical properties and secondary structure analysis unveiled protein characteristics, while homology modelling and molecular docking of DMAPP and IPP ligands assessed binding patterns and interactions with caIDI. Notably, Lys37, Arg72, Lys76, Cys88, Ser89, His90, and Lys113 residues engaged with DMAPP, and Arg72, Lys76, Lys113, Ser89, and His90 residues interacted with IPP. Molecular dynamics simulations affirmed protein-ligand complex stability. IPP established sustained hydrogen bonds with Arg72, Ser89, and Lys113; DMAPP sustained interactions with Lys37, Arg72, Ser89, His90 and Lys113. His41, Glu148, Glu150 engaged with magnesium ion; Val77, Thr78 showed dual interactions with IPP, indicating its substrate binding roles. These findings enhance IDI understanding in Indian Senna which not only plays vital role in isoprenoid biosynthesis but also anthraquinone biosynthesis like sennosides.