Bulk Phase Behavior vs Interface Adsorption: Specific Multivalent Cation and Anion Effects on BSA Interactions

Abstract

Proteins are ubiquitous and play a critical role in many areas from living organisms to protein microchips. In humans, serum albumin has a prominent role in the foreign body response since it is the rst protein which will interact with e.g. an implant or stent. In this study, we focused on the inuence of salts (i.e., dierent cations (Y 3+ , La 3+ ) and anions (Cl − , I − )) on bovine serum albumin (BSA) in terms of its bulk behaviour, as well as its role of charges for the protein adsorption at the solid-liquid interface in order to understand and control the underlying molecular mechanisms and 1 interactions. This is part of our group's eort to gain a deep understanding of proteinprotein and protein-surface interactions in the presence of multivalent ions. In the bulk, we found not only multivalent cation-triggered phase transitions, but also a dependence on the anions. The induced attractive interactions were observed to increase from Cl − < NO − 3 < I − , resulting in iodide preventing re-entrant condensation and promoting liquidliquid phase separation in bulk. Using ellipsometry and a quartz-crystal microbalance with dissipation (QCM-D), we obtained insight into the growth of the protein adsorption layer thickness. Importantly, we found that phase transitions at the substrate can be triggered by certain interface properties, whether they exist in the bulk solution or not.Through the use of a hydrophilic, negatively charged surface (SiO 2 ), the direct binding of anions to the interface was prevented. Interestingly, this led to re-entrant adsorption even in the absence of re-entrant condensation in bulk. However, the overall amount of adsorbed protein was enhanced through stronger attractive protein-protein interactions in the presence of iodide salts. These ndings illustrate how carefully chosen surface properties and salts can directly steer the binding of anions and cations, which guide protein behaviour, thus paving the way for specic/triggered protein-protein, proteinsalt, and protein-surface interactions.

La3+ and Y3+ interactions with the carboxylic acid moiety at the liquid/vapour interface: identification of binding complexes, charge reversal, and detection limits.

“…Nevertheless, trivalent ions are known to play a central role in proteins and colloidal reactivity, being held responsible for crystallization phenomena, phase separation and surface charge reversion. [28][29][30] For example, the adsorption of Fe 3+ and La 3+ on bacterial and bovine serum albumin proteins was revealed to be strongly pH dependent at micromolar concentrations, [31,32] and caused a charge reversion of lipid surfaces starting from sub-micromolar LaCl3 concentrations. [33,34] The complexation of trivalent ions La 3+ and Fe 3+ to the specific carboxylic acid of a fatty acid monolayer has been probed by X-ray reflectivity, X-ray fluorescence, and more recently VSFS.…”

Ion-bridges and lipids drive aggregation of same-charge nanoparticles on lipid membranes

“…Thanks to the increasing ability to engineer NPs with the desired surface properties, and to the fundamental understanding of their behavior in the biological environment, NPs are gaining recognition as models to interpret protein-protein and membrane-protein interactions. Our conclusions may be especially relevant in those cases when protein aggregation is attributed to specific bridging interaction with ions [47][48][49][50] , not only in solution but also in the membrane environment 51 .…”

Electrification of water interface

“…The surface affinities of other divalent metal ions like Mn 2+ , Fe 2+ , and Cu 2+ were studied by surface tension measurement [60] and SFG spectroscopy [137]. Trivalent metal ions such as Fe 3+ , Al 3+ , La 3+ , and Y 3+ , have been studied in the context of charge reversal and re-entrant phase transition in protein solutions [176][177][178][179][180][181][182][183][184], but the surface affinity to the air/water interface remains unclear [65]. Some of these divalent and trivalent metal ions are transition metals, and they easily form ion complexes by coordinating various ligand molecules.…”