Mucin−Electrolyte Interactions at the Solid−Liquid Interface Probed by QCM-D

Abstract

The interaction between mucin and ions has been investigated by employing the quartz crystal microbalance technique with measurement of energy dissipation. The study was partially aimed at understanding the adsorption of mucin on surfaces with different chemistry, and for this purpose, surfaces exposing COOH, OH, and CH(3) groups were prepared. Mucin adsorbed to all three types of functionalized gold surfaces. Adsorption to the hydrophobic surface and to the charged hydrophilic surface (COOH) occured with high affinity despite the fact that in the latter case both mucin and the surface were negatively charged. On the uncharged hydrophilic surface exposing OH groups, the adsorption of mucin was very low. Another aim was to elucidate conformational changes induced by electrolytes on mucin layers adsorbed on hydrophobic surfaces from 30 mM NaNO(3). To this end, we investigated the effect of three electrolytes with increasing cation valance: NaCl, CaCl(2) and LaCl(3). At low NaCl concentrations, the preadsorbed layer expands, whereas at higher concentrations of NaCl the layer becomes more compact. This swelling/compacting of the mucin layer is fully reversible for NaCl. When the mucin layer instead is exposed to CaCl(2) or LaCl(3), compaction is observed at 1 mM. For CaCl(2), this process is only partially reversible, and for LaCl(3), the changes are irreversible within the time frame of the experiment. Finally, mucin interaction with the DTAB cationic surfactant in an aqueous solution of different electrolytes was evaluated with turbidimetry measurements. It is concluded that the electrolytes used in this work screen the association between mucin and DTAB and that the effect increases with increasing cation valency.

Influence of ionic strength changes on the structure of pre-adsorbed salivary films. A response of a natural multi-component layer

“…Upon decrease in ionic strength of solvents, where Debye electrostatic screening length becomes larger, the negatively charged oligosaccharide units repel each other stronger, which results in an overall extension of the glycosylated domains. Our results for ionic strengths down to 1 mM NaCl are consistent with studies on purified mucins, where similar degrees of swelling due to decreases in ionic strength have been observed [10,14]. Such effects are expected to be reversible, which was observed previously for simple polyelectrolytes, for example with QCM-D technique by Dutta et al [30].…”

“…The responsiveness of the salivary film is reported in terms of changes in adsorbed mass of salivary proteins, film thickness, hydration, and film viscoelasticity. We compare the results with those reported for model protein layers consisting of purified mucin [10,14], and we discuss mechanism behind observed differences.…”

Comparison of the adsorption kinetics and surface arrangement of “as received” and purified bovine submaxillary gland mucin (BSM) on hydrophilic surfaces

“…This repulsion is however partly screened by the relatively high salt concentration used in this study with a Debye screening length of approximately 10 Å. Lindh et al have previously shown that the presence of electrolytes enhances the adsorption of BSM on negatively charged substrates, due to a decreased BSM-surface charge repulsion [11]. Furthermore, experimental data have shown that substantially more BSM adsorbs to a negatively charged polar substrate compared to an uncharged polar OH-terminated thiol surface [9]. It is therefore reasonable to assume that adsorption of BSM towards a silica/mica substrate is governed by electrostatics and that the driving force for adsorption on negatively charged surfaces is due to the positively charged amine groups of BSM as suggested in a recent report [9].…”

“…A wide range of mucins isolated from different regions and species [7] has been studied in terms of adsorption to solid surfaces. Thus, it has been shown that the adsorbed mucin layer structure depends on the mucin source [8], solution conditions [9,10] and type of substrate [11,9,12] (non polar, polar and polarcharged). Besides mucin there are a large number of other smaller proteins present in mucous with important functions.…”

A miniaturized flow reaction chamber for use in combination with QCM-D sensing

“…Quartz crystal microbalance with dissipation monitoring (QCM-D) (Rodahl and Kasemo 1996) is a sensing method that during the last 10 years has become widely used for characterizing various biointerfaces and biomolecular interactions, in academy, as well as in industry (Feldötö et al 2008;Modin et al 2006;Peh et al 2007;Richter et al 2006). In particular, surface-supported phospholipid bilayers (SLBs) and similar structures are widely explored as model systems to mimic cell membranes (Cho et al 2007;Pfeiffer and Höök 2004;Radler et al 1995;Richter et al 2006;Richter et al 2007;Rossi and Chopineau 2007;Thid et al 2008;Trepout et al 2007).…”