Doxorubicin-driven reconfiguration of BSA-cushioned DPPC liposomes an integrated molecular-dynamics and AFM roadmap...

Albumin is abundant in plasma and can alter how amphipathic drugs interact with cell membranes, but the mechanical consequences of this interaction are not well understood. We combined atomic force microscopy (AFM) and atomistic molecular dynamics (MD) to quantify how bovine serum albumin (BSA) modulates doxorubicin (DOX) interactions with DPPC bilayers. MM-PBSA analysis applied to all-atom MD trajectories suggests moderate DOX binding to BSA (ΔG ≈ -4.5 kcal mol^-1), albeit with considerable uncertainty (±2.9 kcal mol^-1), dominated by dispersion contacts near Sudlow site I. BSA remains folded (backbone RMSD ≈ 0.33 nm), and the DOX-protein minimum heavy-atom contact distance stabilizes at 0.32 ± 0.01 nm. AFM measurements show that BSA-DOX increases bilayer stiffness and rupture resistance (apparent Young's modulus +≈79%; rupture force +≈45%), without measurable changes in bilayer thickness. Mass-density profiles place head-to-head distances between ≈3.6 and 4.6 nm. Dynamic cross-correlation maps reveal anticorrelated hinge blocks in BSA that dissipate ligand-induced stresses on the nanosecond timescale, linking internal protein dynamics to membrane mechanics. Collectively, these results indicate that albumin acts as a mechanically active, hinge-buffered interfacial scaffold that transiently buffers DOX at the membrane interface, redistributing interfacial interactions to stiffen the bilayer without global thickening.