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

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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.