Interfacial properties of NTAIL, an intrinsically disordered protein
Updated 12-10-2017 08:42
|Biophysical Journal (2017) in press|
|Anaïs Bénarouche, Johnny Habchi, Alain Cagna, Ofelia Maniti, Agnès Girard-Egrot, Jean-François Cavalier, Sonia Longhi and Frédéric Carrière|
Intrinsically disordered proteins (IDPs) lack stable secondary and tertiary structure under physiological conditions in the absence of their biological partners and thus exist as dynamic ensembles of interconverting conformers, often highly soluble in water. However, in some cases, IDPs such as the ones involved in neurodegenerative diseases can form protein aggregates and their aggregation process may be triggered by the interaction with membranes. While the interfacial behaviour of globular proteins has been extensively studied, experimental data on IDPs at the air/water (A/W) and water/lipid interfaces are scarce. We studied here the intrinsically disordered C-terminal domain of the Hendra virus nucleoprotein (NTAIL) and compared its interfacial properties to those of lysozyme that is taken as a model globular protein of similar molecular mass. Adsorption of NTAIL at the A/W interface was studied in the absence and presence of phospholipids using Langmuir films, polarization modulated-infrared reflection–absorption spectroscopy (PM-IRRAS) and an automated drop tensiometer for interfacial tension and elastic modulus determination with oscillating bubbles. NTAIL showed a significant surface activity, with a higher adsorption capacity at the A/W interface and penetration into egg phosphatidylcholine monolayer compared to lysozyme. While lysozyme remains folded upon compression of the protein layer at the A/W interface and shows a quasi-pure elastic behaviour, NTAIL shows a much higher molecular area and forms a highly viscoelastic film with a high dilational modulus. A new disorder-to-order transition is thus observed for the NTAIL protein that folds into an anti-parallel beta-sheet at the A/W interface and presents strong intermolecular interactions.