Adsorption of modified HIV-1 capsid p24 protein onto thermosensitive and cationic core-shell poly(styrene)-poly(N-isopropylacrylamide) particles

The adsorption of HIV-1 capsid p24 protein bearing six histidine residues (named RH24) onto well-characterized thermosensitive and cationic poly(styrene)-poly(N-isopropylacrylamide) core-shell particles was investigated as a function of temperature, pH, incubation time, and salinity. The maximum amount of adsorbed RH24 was observed when the temperature was above the lower critical solution temperature (LCST) of the hydrogel, whereas a negligible adsorbed amount occurred below the LCST. Adsorption isotherms were then determined above the LCST and exhibited well-defined plateaus, which were pH and ionic strength dependent. Isotherm data were tentatively discussed using the Freundlich power law, from which the standard free enthalpy of protein adsorption was estimated. The adsorption behavior of protein was mainly governed by hydrophobic interactions above the LCST; however, differences between the two latexes gave evidence that electrostatic forces also played a significant role.