Air-Water Interfacial Adsorption of the Chaperone Protein DNAJB6b

Aberrant protein aggregation into amyloid fibrils is often catalyzed by interfaces. Therefore, it is important to characterize the surface activity of chaperone proteins having the ability to suppress amyloid formation. The air-water interface is of large practical significance in experimental setups used to study aggregation kinetics in vitro, but in addition, the binding of chaperones to hydrophobic patches on their clients may also be considered as a consequence of interfacial interactions. Here, we have studied the air-water interfacial adsorption of the human chaperone protein DNAJB6b by using hanging drop tensiometry. The dynamic surface tension exhibited a characteristic pattern in a concentration-dependent manner. First, there was an induction period during which the surface tension was close to that of the buffer and then the surface tension quite suddenly decreased, followed by a final semistable regime. DNAJB6b formed an apparently irreversibly adsorbed and elastic surface layer on the timescale of the experiments (about 2 h). The collapse of the surface layer and micelle-like clustering of DNAJB6b in the bulk likely both limit the highest attainable surface pressure. We developed a theoretical model that could successfully reproduce the main features of the results. In addition to the relevance for this specific chaperone system, the adsorption behavior of DNAJB6b was similar to that of other proteins. Thus, the framework for the model we propose might also be significant for protein adsorption in general.