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Ribosome Inactivating Proteins (RIPs) act by irreversibly depurinating the 28S rRNA ricin-sarcin loop (SRL) of the eukaryotic ribosome resulting in protein synthesis inhibition. In general, they consist of two variants: Type I which is single chained (∼30 kDa), and Type II, a more toxic variant which is a Type I N-glycosidase chain covalently linked to a lectin chain. These proteins are believed to play a pivotal role in defence mechanisms. Intriguingly, non-toxic variants of such toxic proteins do exist in nature. To explore their mode of action, in the present study we have selected three toxic (Ricin, Ebulin and HmRIP) as well as two non-toxic (BGSL and SGSL) RIPs and performed molecular docking and molecular dynamic simulations with the SRL loop. This study throws light on the structural stability and plasticity of the toxic and non-toxic RIP complexes. Furthermore, analysis of the active site cavity volume and binding free energy calculations reveal that the SRL, particularly the specific adenine (A4605), is relatively unstable in the case of non-toxic RIPs which is also supported by the free binding energy calculations, and the pocket size analysis indicates the abnormal increase in active site cavity volume of non-toxic RIPs with time. This first-of-its-kind comprehensive study of toxic and non-toxic RIPs gives insights about the mode of action and the dynamic nature of their interaction with the SRL loop. These observations will be helpful in the development of toxoids against RIPs and also in designing novel therapeutic approaches against human diseases.

Plant species from the genus Andrographis were used in Ayurveda and in other folklore medicines for treating ailments for centuries. In this study, we have hypothesized to evaluate the secondary metabolites as potent anti-inflammatory agents from the genus Andrographis. A library of secondary metabolites of the said genus was curated from the PubChem database and was subjected to energy minimization using UCSF Chimera software employing the AMBER force field. Initially, molecular docking was performed to evaluate the binding affinity of the curated library against the enzymes cyclooxygenase-1 (COX-1), cyclooxygenase-2 (COX-2), and 5-Lipoxygenase (5-LOX) using AutoDock Vina. This resulted in shortlisting of two metabolites Echioidinin 5-O-glucoside was bound and 5,2',6'-Trihydroxy-6,7,8-trimethoxy flavone 2'-O-glucoside with high binding affinity than standard drugs Ibuprofen and Zileuton. In addition, molecular dynamic simulation studies confirm that these compounds form relatively more stable complexes than standard drugs with the above-said enzymes. The free binding energy values using MMGBSA of the above said ligands with COX-1, COX-2, and 5-LOX were found to be -49.18 kcal/mol, -38.60 kcal/mol, and -54.27 kcal/mol respectively, Whereas the standards have -21.77 kcal/mol, -9.96 kcal/mol, and -10.29 kcal/mol. Moreover, the in-silico ADMET analysis confirms the druggability of the shortlisted compounds. Later, this work will act as a base for in-vitro and in-vivo experimental studies to validate the anti-inflammatory potential of the same.Communicated by Ramaswamy H. Sarma.