ABSTRACT
We present a model system to demonstrate that the positioning of biomolecules (membrane proteins) in a nonnative, complex thin film environment can be regulated by the phase behavior of film components. Partial separation between an amphiphilic polymer and a lipid drives the protein to a fluid phase, mechanically more similar to a cellular bilayer.
Subject(s)
1,2-Dipalmitoylphosphatidylcholine/analogs & derivatives , Lipid Bilayers/chemistry , Membrane Proteins/chemistry , Oxazoles/chemistry , Polymers/chemistry , Porins/chemistry , 1,2-Dipalmitoylphosphatidylcholine/chemistry , Fluorescent Dyes , Microscopy, Atomic Force , Phase Transition , Succinimides , Surface-Active Agents/chemistryABSTRACT
An easy route to planar solid-supported polymer membranes by vesicle spreading is described. Pre-organized poly(butadiene)-block-poly(ethylene oxide)(PB-PEO) assemblies were spread on two different supports, i.e. strongly hydrophilic glass surfaces and ultrasmooth gold substrates. Polymer membranes were produced on a hydrophilic support by spreading hydroxyl-functionalized polymer vesicles, while covalently immobilized polymer membranes were obtained by spreading LA-functionalized polymer vesicles on gold substrates. Covalently bound membranes were further incubated with the peptide polymyxin B. Interactions with the polymer membrane were detected by EIS. These systems are of great interest to fundamental membrane science and have potential in technological applications, such as drug screening and (bio)sensing.
Subject(s)
Butadienes/chemistry , Gold/chemistry , Membranes, Artificial , Polyethylene/chemistry , Polymyxin B/chemistry , Biosensing Techniques/methods , Drug Evaluation, Preclinical/methods , Surface PropertiesABSTRACT
The interaction of the proteins bovine serum albumin (BSA), lysozyme (Lys), lactoferrin (Lf), and fibronectin (Fn) with surfaces of protein-resistant poly(ethylene oxide) (PEO) and protein-adsorbing poly(acrylic acid) (PAA) fabricated by plasma-enhanced chemical vapor deposition has been studied with quartz crystal microbalance with dissipation monitoring (QCM-D). We focus on several parameters which are crucial for protein adsorption, i.e., the isoelectric point (pI) of the proteins, the pH of the solution, and the charge density of the sorbent surfaces, with the zeta-potential as a measure for the latter. The measurements reveal adsorption stages characterized by different segments in the plots of the dissipation vs frequency change. PEO remains protein-repellent for BSA, Lys, and Lf at pH 4-8.5, while weak adsorption of Fn was observed. On PAA, different stages of protein adsorption processes could be distinguished under most experimental conditions. BSA, Lys, Lf, and Fn generally exhibit a rapid initial adsorption phase on PAA, often followed by slower processes. The evaluation of the adsorption kinetics also reveals different adsorption stages, whereas the number of these stages does not always correspond to the structurally different phases as revealed by the D- f plots. The results presented here, together with information obtained in previous studies by other groups on the properties of these proteins and their interaction with surfaces, allow us to develop an adsorption scenario for each of these proteins, which takes into account electrostatic protein-surface and protein-protein interaction, but also the pH-dependent properties of the proteins, such as shape and exposure of specific domains.
