No abstract

Toxoplasma gondii an obligate intracellular parasite causes toxoplasmosis in homeothermic animals. Host invasion of this parasite is mediated by the formation of Moving Junction (MJ) complex which encompasses a network of microneme and Rhoptry Neck proteins (RONs) 2/4/5/8. Among these proteins, RON4 is the only cytosolic secretory protein that is considered as a crucial member, as it directly facilitates the motility of MJ complex by interacting with host tubulin. It is also prominently localized at the host-pathogen interface during the invasion, thus projecting it as a potential drug target. The structure of RON4 is yet to be crystallized. Hence, in this study, fold recognition and Free Energy Landscape sampling was performed to predict the plausible 3D structure of RON4. Further, its interacting pattern with the reported crystal structure of human tubulin was analyzed using molecular docking. Subsequently, a β-tubulin based inhibitory peptides were derived based on its interacting interface observed in RON4-β-tubulin docked complex. Following which, a stepwise validation of these peptides for various physico-chemical properties and its homology with antimicrobial peptides were also screened. The peptide (RT_pep) surpassing all these validation filters was modeled and its stability was analysed by Molecular Dynamics simulation. To validate further, the stable conformation of the RT_pep was docked to RON4. Finally, essential molecular dynamics simulation was conducted to determine the stability and atomic motions of native RON4 and also to decipher its association with β-tubulin and RT_pep. All these analyses cumulatively suggest the therapeutic potential of RT_pep in targeting toxoplasmosis.

The conventional use of antibiotics for the treatment of infectious keratitis currently faces two major challenges: poor drug penetration and the emergence of antibiotic resistance in microbial strains. Cell-penetrating peptides (CPPs) with antimicrobial properties have the potential to address these challenges. However, their mode of action, mechanism of uptake, and interaction potential have not been explored in detail. In this study, we probed the mechanism of uptake and interaction potential of our previously designed peptides (VRF005 and VRF007). Our results showed that VRF005 undergoes direct translocation and induces a rough membrane surface, whereas VRF007 undergoes clathrin-mediated endocytic uptake. The gel shift assay showed that VRF005 is bound to genomic DNA, whereas VRF007 is bound to chitin and β-D-glucan. Gene expression studies revealed the effect of peptide VRF005 on Candida albicans transcription. Molecular docking and simulations showed that VRF005 forms noncovalent interactions (such as H-bonding and water bridges) with natamycin. It exhibited synergistic antifungal activity in the colony-forming assay. VRF005, functionalized in the polycaprolactone fiber matrix, showed sustained delivery and antifungal activity.

Heparanase (HPSE) is an endo-β-D-glucuronidase that has diverse functions in mammals which includes cell survival, cell adhesion and cell migration. HPSE features both enzymatic and non-enzymatic functionalities in a pH dependent manner. Hence, in this study, an extensive molecular dynamics simulation, molecular docking, protein Angular dispersion analysis were performed for apo form and holo forms to understand its conformational changes at varied pH conditions. On comparative conformational analysis of apo and holo forms, it was inferred that the HSPE has undergone pH dependent structural changes, thereby affecting the binding of Heparan sulfate proteoglycan (HSPG). Moreover, HPSE also showed favourable structural changes for optimal binding of HSPG at pH 5.0 and 6.0, as inferred from functional flap displacements within HPSE. Thus, this study provides significant insights on optimal pH for HPSE to exhibit its enzymatic activity. The outcome of this study shall aid in ideal lead generation for targeting HPSE mediated disease conditions.

Fig S1. (a) Snapshot of membrane system of Porin embedded in bilayer lipid of DMPC, and the structure over view and it is seen in cylindrical shape; (b) view of Porin from extracellular side of pore channel.