Protein Adsorption onto Polyelectrolyte Layers: Effects of Protein Hydrophobicity and Charge Anisotropy

Abstract

Ellipsometry was used to investigate the influence of ionic strength (I) and pH on the adsorption of bovine serum albumin (BSA) or beta-lactoglobulin (BLG) onto preabsorbed layers of two polycations: poly(diallyldimethylammonium chloride) (PDADMAC) or poly(4-vinylpyridine bromide) quaternized with linear aliphatic chains of two (QPVP-C2) or five (QPVP-C5) carbons. Comparisons among results for the three polycations reveal hydrophobic interactions, while comparisons between BSA and BLG-proteins of very similar isoelectric points (pI)-indicate the importance of protein charge anisotropy. At pH close to pI, the ionic strength dependence of the adsorbed amount of protein (Gamma) displayed maxima in the range 10 < I < 25 mM corresponding to Debye lengths close to the protein radii. Visualization of protein charge by Delphi suggested that these ionic strength conditions corresponded to suppression of long-range repulsion between polycations and protein positive domains, without diminution of short-range attraction between polycation segments and locally negative protein domains, in a manner similar to the behavior of PE-protein complexes in solution. (1-4) This description was consistent with the disappearance of the maxima at pH either above or below pI. In the former case, Gamma values decrease exponentially with I(1/2), due to screening of attractions, while in the latter case adsorption of both proteins decreased at low I due to strong repulsion. Close to or below pI both proteins adsorbed more strongly onto QPVP-C5 than onto QPVP-C2 or PDADMAC due to hydrophobic interactions with the longer alkyl group. Above pI, the adsorption was more pronounced with PDADMAC because these chains may assume more loosely bound layers due to lower linear charge density.

β-Lactoglobulin (BLG) binding to highly charged cationic polymer-grafted magnetic nanoparticles: Effect of ionic strength

“…Increasing the salt concentration eventually raises the dipole moment and the dominant effect becomes to be charge patch mechanism caused by the charge anisotropy. As revealed by us before, BLG dimer contains region with a concentrated negative charges accounts for a strong dipole which differs from some other proteins with relative disperse charges such as BSA [24,40] . Therefore, in order to understand the behavior of the non-monotonic ionic strength dependence of binding, Delphi electrostatic modelling was used to visualize the potential contours of BLG.…”

Thermoresponsive behavior of micellar aggregates from end-functionalized PnBA-b-PNIPAM-COOH block copolymers and their complexes with lysozyme

“…Electrostatic interactions, entropic counterion release forces 5 and hydrophobic interactions take part in protein polyelectrolyte binding 6 .…”

A neutron reflection study of adsorbed deuterated myoglobin layers on hydrophobic surfaces

“…Protein adsorption on solid surfaces in contact with an aqueous environment has been a very active field of research for the last few decades: the understanding of the different aspects of the process is a crucial step for many practical applications with many ramifications in different disciplines, from the use of protein for colloid stabilization, development of surgical implants and biosensors, functioning of cell membranes to mention some [1,2]. The adsorption process is a complex phenomenon driven by surfaceprotein interactions -van der Waals forces, electrostatic and hydrophobic interactions [3,4].…”