Camille Loupiac

Structure of calcium and zinc pectinate films investigated by FTIR spectroscopy.

Calcium and zinc pectinate gels were prepared using a method which allowed calcium or zinc to diffuse from the cross-linking solution through a dialysis membrane to form a gel with amidated low-methoxyl pectin. The gel thus obtained was then dried, and the film structure was studied using FTIR spectroscopy as a function of the cation content (0%, 5%, 10%, and 15% w/v). Important consideration was given to the three functional groups (amide, carboxyl ester, and carboxylate groups) present in the pectin. When the zinc content was increased, the three wavenumber values corresponding to these three functional groups did not change significantly, while for calcium pectinate, the three wavenumber values were shifted profoundly when the amount of calcium ions changed. These results confirm that calcium ions could form stable interactions with carboxylate groups as described by the eggbox model [Grant, G.T.; Morris, E.R.; Rees, D.A.; Smith, P.J.C.; Tho, D. FEBS Lett.1973, 32, 195-198] while the lower coordination number of zinc does not permit a structured gel to develop.

Myoglobin on Silica: A Case Study of the Impact of Adsorption on Protein Structure and Dynamics

If protein structure and function changes upon adsorption are well documented, modification of adsorbed protein dynamics remains a blind spot, despite its importance in biological processes. The adsorption of metmyoglobin on a silica surface was studied by isotherm measurements, microcalorimetry, circular dichroïsm, and UV-visible spectroscopy to determine the thermodynamic parameters of protein adsorption and consequent structure modifications. The mean square displacement and the vibrational densities of states of the adsorbed protein were measured by elastic and inelastic neutron scattering experiments. A decrease of protein flexibility and depletion in low frequency modes of myoglobin after adsorption on silica was observed. Our results suggest that the structure loss itself is not the entropic driving force of adsorption.

Probing protein-membrane interactions using solid supported membranes.

Tethered bilayer lipid membranes have been used as a model system to mimic the interactions between the whey protein β-lactoglobulin and a lipid interface. The approach allowed for a detailed study of the lipid-protein interactions, the results being of possible importance in food and cosmetic applications. For such applications, lipid-protein interactions and the interfacial behavior are vital factors in controlling and manipulating process conditions such as emulsion stabilization and gelification. Lipid composition as well as the structural properties of the protein governed their interactions, which were probed by a combination of surface plasmon spectroscopy, neutron reflectivity, and electrochemical impedance spectroscopy. Comparison of results obtained using native and a partially unfolded protein indicated that the protein preferentially forms loosely packed layers at the lipid interface.

Protein-lipid interactions at the air-water interface.

Protein-lipid interactions play an important role in a variety of fields, for example in pharmaceutical research, biosensing, or food science. However, the underlying fundamental processes that govern the interplay of lipids and proteins are often very complex and are therefore studied using model systems. Here, Langmuir monolayers were used to probe the interaction of a model protein with lipid films at the air-water interface. The protein beta-lactoglobulin (beta lg) is the major component in bovine milk serum, where it coexists with the milk fat globular membrane. During homogenization of milk, beta lg adsorbs to the interface of lipid fat globules and stabilizes the oil-in-water emulsion. pH and ionic strength of the subphase had a significant effect on the surface activity of the protein. Additionally, by using lipids with different charges, it could be shown that the interactions between beta lg and a phospholipid layer were driven by hydrophobic as well as by electrostatic interactions. beta lg preferentially interacted with phospholipids in an unfolded state. This could be either achieved by denaturation at the air-water interface or due to electrostatic interactions that weaken the intramolecular forces of the protein.