Structural insights into the electrostatic interactions in human serum albumin dimerization patterns and dipyridamole interaction.

Human serum albumin (HSA) is a ubiquitous, multifunctional protein responsible for the body-wide distribution of both endogenous metabolites' nutrients and exogenous pharmaceuticals. Its inherent properties, mainly its ability to transcytosis and leak into the tissue lumens and having multiple ligand-binding sites, have rendered HSA an exploitable building block in nanoparticle-based drug delivery systems, particularly in cancer targeting. In this study, we present high-resolution crystallographic data (PDB ID: 9V61) supported structure revealing two distinct dimerization patterns of HSA, obtained under high-concentration crystallization conditions, in addition to results from dipyridamole dockings. Both dimer types demonstrate extensive interface areas and a significant number of electrostatic interactions. Comparative analysis with previously reported dimer structure (3JQZ) and other high-interface-area structures, (5Z0B, 8CKS) indicate similarities in contact regions, but unique residue-level differences in biophysical electrostatic bonding interactions. Interface surface area distribution and space group histograms further support the rarity and potential therapeutic relevance of the identified dimer forms. Importantly, these dimer configurations do not disrupt Sudlow's drug-binding sites, which is important as the dipyridamole docking analysis presents a strong affinity to Sudlow site I, not affecting their utility in engineered drug delivery. Our findings open new avenues for structure-based mutagenesis and nanoparticle design strategies centered on HSA dimerization dynamics.