Session: Basic Research in Colloids, Surfactants and Interfaces:

Interactions between proteins and surfactants play an important role in food processing, pharmaceuticals, cleaning agents, protein purification, and the characterization of membrane proteins. Characterizing these interactions and the structure of protein-surfactant complexes is necessary for proper product formation and development as they can affect enzyme activity, emulsion and foam formation and stability. While ionic surfactants, such as sodium dodecyl sulfate (SDS), are known to perturb protein tertiary and secondary structure at low concentrations, the effects of nonionic surfactants, such as lauryldimethylamine oxide (LDAO), on protein stability have been less studied. We investigated the impact of LDAO on the structure of β-Lactoglobulin (βLG) using a variety of biophysical techniques. Pyrene fluorescence and pendant drop tensiometry shows that the critical micelle concentration (CMC) of LDAO, 1.6 mM, is unaffected by the presence of βLG. Low concentrations of LDAO, below the CMC, have weak surfactant interactions with βLG, causing minimal change in structure. At and above the CMC of LDAO, protein-surfactant complexes form and loss of tertiary structure is observed. Secondary structure of βLG remains until a concentration of 20 mM is reached, much above the CMC for LDAO. SAXS analysis revealed a similar change in globular structure above the LDAO CMC. This indicates presence of LDAO micelles is important for denaturation and follows an unfolding mechanism different from that seen in ionic surfactants. Currently, mixtures of nonionic and ionic surfactants are being assessed for changes in CMC as well as through interactions with βLG.

Jason Berberich

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