Role of Protein Unfolding in Monolayer Formation on Air−Water Interface

Abstract

Molecular exchange kinetics between a monolayer of antibody molecules formed on the air−water interface and the protein solution was studied by means of fluorescent labeling. It was shown that there is no inclusion of dissolved molecules in the previously formed monolayer during even 6 h of exposure regardless of monolayer surface density. The surface activity of IgG and horseradish peroxidase molecules was studied by means of surface compression isotherms, and the specific biological activity of the monolayers formed from these proteins was measured by enzyme and immunoassay techniques. It was shown that the surface activity of the proteins increases while specific biological activity decreases with exposure of the molecules on the water surface. Since the same effects were caused by denaturing agents, we propose that the surface activity of the proteins and the absence of surface−volume exchange are due to partial unfolding of the molecules which takes place on the water surface. Two models of the partial unfolding are discussed: complete denaturation of some part of the molecules and partial unfolding of each molecule. The process of surface denaturation was shown to be slow and controllable. One can achieve a pronounced increase of protein surface activity with low degradation of the specific biological activity of the monolayer; thus, it can be used in the practice of protein Langmuir film deposition.

Albumin binding and insertion into PS-b-PEO monolayers at air–water interface

“…The HSA layer thickness on control ODT-gold surface was 1.2 nm (Fig 7). This thickness was lower than 1.8 nm measured by SPR for an HSA monolayer on a similar substrate [17], but was similar to the results of HSA adsorption experiments carried out in a similar time frame [38,39].…”

“…Both HSA and FER, used in this study as models for small and large proteins, are known to adsorb readily from dilute solutions to a variety of interfaces [35][36][37][38][39]. Saturation adsorption of HSA and FER is approximately of 2.5 × 10 −7 and 6.3 × 10 −7 g/cm 2 , respectively [18,37].…”

Solid-State NMR Characterization of Gas Vesicle Structure

“…Gas vesicles function by forming an interface between the aqueous phase and the air inside the vesicle. In contrast, ordinary proteins function fully immersed in condensed aqueous or lipid phases, and tend to unfold on exposure to an air-liquid interface (51,52), with the hydrophobic core exposed to the air. On the other hand, extended b-sheets with an alternating polar-nonpolar amino acid sequence are stable at an air-water interface, as their amphipathic nature allows them to expose the hydrophobic side chains on one face to the air, and the hydrophilic side chains on the other face to the water.…”

Chemically Modified Human Immunoglobulin G: Hydrophobicity and Surface Activity at Air/Solution Interface

“…These values are close to those obtained by MacRitchie (27)(28)(29)(30) for the human ␥-globulin (110 -130 Å 2 ), but much smaller than those expected from the "T"-shaped structure of the IgG molecule (47) with the "cap" (F ab fragments) and "leg" (F c fragment), having ellipsoidal cross sections (142 ϫ 50 ϫ 40 and 85 ϫ 45 ϫ 38 Å, respectively). For comparison, ⌸-A curves for IgG give values of cross-sectional areas, compatible with its molecular dimensions (31)(32)(33)(34)(35)(36). The small values of ⌬A compared to the actual molecular size are a common phenomenon for many proteins at the air/water interface, irrespective of their molecular weights (1), and may be explained according to MacRitchie's assumption that the values obtained from the kinetic data reflect only the transition state configuration, with segments of several amino acid residues in contact with the surface (30).…”