Density functional theory based probe of the affinity interaction of saccharide ligands with extra-cellular sialic acid residues

Changes in glycosylation pattern leads to malignant transformations among the cells. In combination with upregulated actions of sialyltransferases, it ultimately leads to differential expression of sialic acid (SA) at cell surface. Given its negative charge and localization to extracellular domain, SA has been exploited for the development of targeted theranostics using approaches, such as, cationization and appending recognition saccharides on carrier surface. In this study, we have performed quantum mechanical calculations based on density functional theory (DFT) to study the interaction of saccharides with extracellular SA. Gradient-corrected DFT with the three parameter function (B3) was utilized for the calculation of Lee-Yang-Parr (LYP) correlation function. Atomic charge, vibrational frequencies and energy of the optimized structures were calculated through B3LYP. Our calculations demonstrate a stronger galactose-sialic acid interaction at tumour-relevant low pH and hyperthermic condition. These results support the application of pH responsive delivery vehicles and targeted hyperthermic chemotherapy for eradicating solid tumour deposits. These studies, conducted a priori, can guide the formulation scientists over appropriate choice of ligands and their applications in the design of 'smart' theranostic tools.

Binding forces between a novel Schiff base palladium(II) complex and two carrier proteins: human serum albumi and β-lactoglobulin

Ligand binding studies on carrier proteins are crucial in determining the pharmacological properties of drug candidates. Here, a new palladium(II) complex was synthesized and characterized. The in vitro binding studies of this complex with two carrier proteins, human serum albumin (HSA), and β-lactoglobulin (βLG) were investigated by employing biophysical techniques as well as computational modeling. The experimental results showed that the Pd(II) complex interacted with two carrier proteins with moderate binding affinity (K_b ≈ .5 × 10⁴ M^-1 for HSA and .2 × 10³ M^-1 for βLG). Binding of Pd(II) complex to HSA and βLG caused strong fluorescence quenching of both proteins through static quenching mechanism. In two studied systems hydrogen bonds and van der Waals forces were the major stabilizing forces in the drug-protein complex formation. UV-Visible and FT-IR measurements indicated that the binding of above complex to HSA and βLG may induce conformational and micro-environmental changes of two proteins. Protein-ligand docking analysis confirmed that the Pd(II) complex binds to residues located in the subdomain IIA of HSA and site A of βLG. All these experimental and computational results suggest that βLG and HSA might act as carrier protein for Pd(II) complex to deliver it to the target molecules.