Dynamical and morphological studies on the adsorption and penetration of human serum albumin into phospholipid monolayers at the air/water interface

Abstract

The dynamic adsorption and penetration of human serum albumin (HSA) into the monolayers of five biologically important surfactants—DSPC, DPPC, DMPC, DMPE and DMPA—were systematically studied using Brewster angle microscopy, film balance and pendent drop techniques. Isotherms after different adsorption times show that the presence of HSA changed the monolayer phase behavior (e.g. the shifts of the LE→LC phase transition in the mixed phospholipid/HSA monolayers). Apparent inhomogeneous phases—‘honey-comb’ (J. Mol. Liq., 2001, 90, 149), ‘block’ or ‘stripe’ shape phases are formed due to the adsorption and penetration of HSA into these phospholipid monolayers at the air/water interface. Both the phase behavior changes and the morphological changes were confirmed by our recent structure studies in DPPA/HSA and DPPS/HSA monolayers using X-ray diffraction at grazing incidence, which directly shows that HSA penetration can change the tilt angle of phospholipids. It was found that the adsorption and penetration of HSA strongly depends on the phospholipid head-group structure and the physical state of the phospholipid films. The latter played a dominant role by providing enough space for the penetration of HSA and affecting the hydrophobic interactions of HSA with the aliphatic chains of phospholipids in monolayers at the air/water interface. In general, HSA penetrates more efficiently and quickly into monolayers of phospholipids in liquid state (e.g. DMPC compared to DSPC) and with unprotected charges (e.g. PA compared to PE and PC).