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The adsorption and unfolding kinetics determines the folding state of proteins at the air-water interface and thereby the equation of state

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Author: Wierenga, P.A. · Egmond, M.R. · Voragen, A.G.J. · Jongh, H.H.J.de
Type:article
Date:2006
Institution: TNO Kwaliteit van Leven
Source:Journal of Colloid and Interface Science, 2, 299, 850-857
Identifier: 239372
doi: doi:10.1016/j.jcis.2006.03.016
Keywords: Nutrition · Food technology · Air-water interface · Protein adsorption · Surface denaturation · Surface equation of state · Adsorption · Cytology · Equations of state · Interfaces (materials) · Molecules · Surface properties · Air-water interface · Protein adsorption · Surface denaturation · Surface equation of state · Proteins · beta lactoglobulin · cytochrome c · ovalbumin · water · adsorption · air · article · ellipsometry · kinetics · mathematical analysis · pressure · priority journal · protein folding · protein processing · protein stability · protein structure · surface property · Adsorption · Air · Calorimetry · Cytochromes c · Drug Stability · Kinetics · Lactoglobulins · Ovalbumin · Pressure · Protein Conformation · Protein Denaturation · Protein Folding · Proteins · Surface Properties · Urea · Water

Abstract

Unfolding of proteins has often been mentioned as an important factor during the adsorption process at air-water interfaces and in the increase of surface pressure at later stages of the adsorption process. This work focuses on the question whether the folding state of the adsorbed protein depends on the rate of adsorption to the interface, which can be controlled by bulk concentration. Therefore, the adsorption of proteins with varying structural stabilities at several protein concentrations was studied using ellipsometry and surface tensiometry. For β-lactoglobulin the adsorbed amount (Γ) needed to reach a certain surface pressure (Π) decreased with decreasing bulk concentration. Ovalbumin showed no such dependence. To verify whether this difference in behavior is caused by the difference in structural stability, similar experiments were performed with cytochrome c and a destabilized variant of this protein. Both proteins showed identical Π - Γ, and no dependence on bulk concentration. From this work it was concluded that unfolding will only take place if the kinetics of adsorption is similar or slower than the kinetics of unfolding. The latter depends on the activation energy of unfolding (which is in the order of 100-300 kJ/mol), rather than the free energy of unfolding (typically 10-50 kJ/mol). © 2006 Elsevier Inc. All rights reserved.