Dilatational Rheology of BSA Conformers at the Air/Water Interface

Abstract

To elucidate the role of protein conformation at the air/water interface, we measured the interfacial dilatational rheology of bovine serum albumin (BSA) and β-casein adsorbed over long time periods using a modified dynamic pendant-drop tensiometer. Companion long-time dynamic surface pressure and ellipsometry measurements are also reported. BSA has well-characterized structural isomers (conformers) whose structural transitions depend on solution pH. It is, therefore, possible to establish a connection between protein structure and interfacial rheology without the ambiguity of comparing different proteins. We also studied β-casein to verify the conclusions obtained from BSA. Adsorbed BSA and β-casein protein layers are primarily elastic with the dilatational elastic modulus arising from two contributions: (1) conformational rearrangement following adsorption that leads to formation of an interconnected, samplespanning interfacial protein network (i.e., an interfacial gel), and (2) the intrinsic structural stability of the individual protein units within the network. The latter component is most important to the interfacial dilatational modulus and explains why adsorbed layers of rigid, globular proteins are more elastic than those of flexible, random-coil proteins. We identify a new surface elasticity relaxation mechanism at the interface due to interprotein conformational rearrangement that is enhanced by electrostatic screening.

Temperature is key to yield and stability of BSA stabilized microbubbles

“…At ionic strength of 0.4 M and higher Dibbern, Toublan, and Suslick (2006) observed a decrease in microbubble yield. It has been described in literature (Noskov, Mikhailovskaya, Lin, Loglio, & Miller, 2010;Pereira, Theodoly, Blanch, & Radke, 2003) that a high surface coverage and a more rigid airewater interface at pH close the isoelectric point, or upon salt addition, can be attributed to both the charge and the conformation of the molecules. A decreased repulsion between molecules appears to result in a higher coverage at the airewater interface (Pereira et al, 2003).…”

“…It has been described in literature (Noskov, Mikhailovskaya, Lin, Loglio, & Miller, 2010;Pereira, Theodoly, Blanch, & Radke, 2003) that a high surface coverage and a more rigid airewater interface at pH close the isoelectric point, or upon salt addition, can be attributed to both the charge and the conformation of the molecules. A decreased repulsion between molecules appears to result in a higher coverage at the airewater interface (Pereira et al, 2003). Furthermore, at pH around the isoelectric point and at high ionic strength BSA molecules are in a native, more compact conformation, allowing a more efficient filling of the available space (Noskov et al, 2010).…”

Power-law rheology in the bulk and at the interface: quasi-properties and fractional constitutive equations

“…Two common examples of surface active materials are Acacia gum solutions and BSA solutions, which form the focus of the present study. The surface characteristics of BSA solutions at the air-water interface have been studied extensively using multiple techniques, and it is well established that these solutions form rigid viscoelastic interfaces [43,[53][54][55]. On the other hand, although some interfacial studies have been performed on Acacia gum solutions [49,56,57], there is comparatively less literature available for these solutions.…”

Active Interfacial Shear Microrheology of Aging Protein Films

“…Rheology is intimately coupled to the organization and interactions of the molecules making up these monolayers [4–13]. However, monolayer shear viscosity, especially during adsorption, remains largely unexplored due to the difficulty of decoupling the properties of the two-dimensional interfacial film from those of the three-dimensional fluid [9, 14].…”