Moderate conformational impact of citrate on ovotransferrin considerably increases its capacity to self-assemble at the interface

Abstract

We have compared the behavior of ovotransferrin at the air-solution interface in the presence of a monovalent ion (acetate), or a divalent ion (citrate), the latter being known to induce conformational changes of this protein upon interaction with its iron-binding sites. We have characterised the adsorption layer at the air-water interface in terms of homogeneity, surface concentration excess and rheological properties at pH 4.0. Besides we have investigated the bulk conformation in the presence of the two anions. In the presence of citrate only, interfacial layers display well-defined domains of higher overall surface concentration suggesting multilayers adsorption. Citrate also induces higher helical content and stabilizes the protein against thermal denaturation. Hence we propose that these changes are involved in the propensity of ovotransferrin to self-assemble at the air-water interface resulting in thick and heterogeneous interfacial layer.

Protein Transport upon Advection at the Air/Water Interface: When Charge Matters

“…56,57 Far from these conditions, for single-protein systems, multilayer adsorption at the air−water interface has essentially been observed under conditions of minimal repulsion at the isoelectric point pH 34 or at high ionic strength 58 in the presence of protein aggregates in the bulk solution 59 or in the presence of denaturant. 60 Far from the isoelectric point pH, multilayers formed by single-protein solutions were only mentioned for positively charged lysozyme at pH 7.0, 2,19 for positively charged ovotransferin 51 and for negatively charged beta and kappa casein 21 while the propensity of ovalbumin to form multilayers when carrying a net positive charge, shown in this report, has never been mentioned before to our knowledge.…”

“…Far from the isoelectric point pH, multilayers formed by single-protein solutions were only mentioned for positively charged lysozyme at pH 7.0, , for positively charged ovotransferin and for negatively charged beta and kappa casein while the propensity of ovalbumin to form multilayers when carrying a net positive charge, shown in this report, has never been mentioned before to our knowledge.…”

“…Such asymmetry cannot be tested for lysozyme which is positively charged at all experimental pH (with its pI being about 10.7). However, this trend has been evidenced on ovotransferrin, which forms multilayers when positively charged 51 and monolayers when negatively charged. 52 All of these results and observations together suggest that protein−protein interaction is repulsive (or at least not attractive) for negatively charged ovalbumin and prevents the formation of multilayers after the formation of the first interfacial layer, despite the advection flow which brings proteins toward the interface.…”

“…Such asymmetry cannot be tested for lysozyme which is positively charged at all experimental pH (with its p I being about 10.7). However, this trend has been evidenced on ovotransferrin, which forms multilayers when positively charged and monolayers when negatively charged …”

Cold-Set Emulsion Gels Costabilized by Kidney Bean Protein Isolate and Basil Seed Gum as Astaxanthin Carriers: Improved Stability and Bioaccessibility

“…Since the gel strength was related to the size and the number of oil droplets, the increase of oil fraction was beneficial to the filling of oil droplets in a gel matrix. 33 Second, sodium citrate weakened the electrostatic repulsion between protein molecules and promoted protein self-assembly, 34 thereby enhancing the electrostatic and hydrophobic interactions between KPI molecules to induce the formation of cold-set gel. Additionally, the pH of the emulsion was lowered below the isoelectric point of the KPI by the addition of GDL, which led to the isoelectric flocculation of the emulsion droplets and promoted the formation of the gel structure.…”