A modular tethering complex for endosomal recycling.

How proteins migrate through the interconnected organelles of the endolysosomal system is poorly understood. A piece of the puzzle has been added with the identification of a complex of tethering factors that functions in the recycling of proteins towards the cell surface

Dry-heating makes hen egg white lysozyme an efficient foaming agent and enables its bulk aggregation.

International audienceDry-heating is considered to be one of the most promising approaches to improving the functionality of food proteins. It has been shown that even if only minor structural modifications occur during dry-heating, the foaming properties of proteins are highly improved. With the recent results obtained in the field of foam stabilization by nanoparticles or protein aggregates in mind, a study was undertaken on the impact of dry-heating of lysozyme, used as a model protein, on its foaming properties. This work highlighted the fact that dry-heated hen egg white lysozyme simultaneously exhibited enhanced foaming properties and aggregation capacity. Although the conditions that favored bulk aggregation (high ionic strength, pH, treatment duration, and protein concentration) also favored foaming properties, the large bulk aggregates were not essential to obtain the best functionality. It is envisaged that heat-treated lysozyme may self-associate at the air/water interface, stabilizing air bubbles

Heat treatment of ovalbumin powder: interfacial and foaming properties of the different molecular species generated.

International audienceDry heating is performed in egg product industries to pasteurise egg white powder. This treatment (55 to 80°C during a few days) is also used to improve egg white powder functional properties among other foaming properties. Several studies have shown this foaming properties' improvement with dry heating length (Kato et al, 1989; Baron et al, 2003; Van der Plancken et al, 2007; Talansier et al, 2009) that Kato et al (1989) attributed to protein surface hydrophobicity increase. However, during these treatments, soluble and insoluble covalent aggregates were also generated (Kato, 1989; Van der Plancken et al, 2007; Talansier et al, 2009) that may be involved in foaming properties improvement. Conclusions from such a complex protein solution as egg white are difficult to draw; this is the reason why we choose ovalbumin, the major egg white protein (54% of total protein amount) to identify the molecular species generated by dry heating that are responsible for foaming properties' improvement. Ovalbumin foaming properties are improved after dry heating (Kato, 1990a) and the protein undergoes some mild conformational changes close to the molten globule state as well as aggregation driven by hydrophobic interactions and disulfide bonding (Kato, 1990b; Matsudomi, 2001). The present study has been performed to identify the molecular species generated by dry heating responsible for foaming properties improvement. Most of the data of the literature were confirmed as we found that ovalbumin aggregated and that deamidation occurred. We also identified less negatively charged ovalbumin that we attributed to dephosphorylation. We performed surface pressure and ellipsometric angle measurement on dry heated ovalbumin but also on dephosphorylated, desamidated and aggregated forms. Dry heated ovalbumin shows faster adsorption kinetics to air water interface than non-treated one. However the equilibrium surface pressure and surface concentration are quite close. Shear elastic constant measurement showed far higher values for dry heated Ovalbumin. Foaming properties of the different molecular species were also measured when possible. This multidimensional approach helped in the understanding of the characteristic of the interfacial film that explain foaming properties

Strong improvement of interfacial properties can result from slight structural modifications of proteins: the case of native and dry-heated lysozyme.

International audienceIdentification of the key physicochemical parameters of proteins that determine their interfacial properties is still incomplete and represents a real stake challenge, especially for food proteins. Many studies have thus consisted in comparing the interfacial behavior of different proteins, but it is difficult to draw clear conclusions when the molecules are completely different on several levels. Here the adsorption process of a model protein, the hen egg-white lysozyme, and the same protein that underwent a thermal treatment in the dry state, was characterized. The consequences of this treatment have been previously studied: net charge and hydrophobicity increase and lesser protein stability, but no secondary and tertiary structure modification (Desfougères, Y.; Jardin, J.; Lechevalier, V.; Pezennec, S.; Nau, F. Biomacromolecules 2011, 12, 156-166). The present study shows that these slight modifications dramatically increase the interfacial properties of the protein, since the adsorption to the air-water interface is much faster and more efficient (higher surface pressure). Moreover, a thick and strongly viscoelastic multilayer film is created, while native lysozyme adsorbs in a fragile monolayer film. Another striking result is that completely different behaviors were observed between two molecular species, i.e., native and native-like lysozyme, even though these species could not be distinguished by usual spectroscopic methods. This suggests that the air-water interface could be considered as a useful tool to reveal very subtle differences between protein molecules