Journal Article Co-aggregation of ovalbumin and lysozyme

Iwashita, Kazuki  ,  Handa, Akihiro  ,  Shiraki, Kentaro

67pp.206 - 215 , 2017-06 , Elsevier
Hen egg white has excellent heat-induced gelation properties. However, the molecular mechanisms underlying the aggregation of egg white proteins have not been elucidated due to their complex composition. Here, we focused on the thermal co-aggregation process of the main component, ovalbumin (OVA), with well-studied lysozyme (LYZ) in terms of protein composition, aggregation rate, intermolecular forces, and morphology. Size exclusion chromatographic analysis of OVA–LYZ mixture by heat treatment at 70 °C indicated that the aggregation-rate constant of LYZ increased 64-fold in the presence of equimolar OVA. In contrast, the aggregation rate of OVA was not dependent on the presence of LYZ. Enzyme assay and SDS-PAGE analysis showed that LYZ forms precipitates with unfolded OVA via reversible non-covalent interactions and irreversible disulfide bonds. The unfolding of OVA triggers co-aggregation by exposure of the aggregation-prone region, followed by disulfide bond exchange between OVA and LYZ. LYZ links covalently to small OVA aggregates through disulfide bonds, leading to the hierarchical growth of OVA–LYZ aggregates with larger networks. These results provide information regarding the thermal co-aggregation of proteins in hen egg white.

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