A phenomenological description of BslA assemblies across multiple length scales.
Bottom Line: Here we describe several self-assembled structures formed by BslA, both at interfaces and in bulk solution, over a range of length scales spanning from nanometres to millimetres.First, we observe transiently stable and highly elongated air bubbles formed in agitated BslA samples.Second, we describe elongated tubules formed by BslA interfacial films when shear stresses are applied in both a Langmuir trough and a rheometer.
Affiliation: School of Physics and Astronomy, University of Edinburgh, James Clerk Maxwell Building, Peter Guthrie Tait Road, Edinburgh EH9 3FD, UK.Show MeSH
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Mentions: We then studied the dissipation of BslA-stabilized bubbles under different solution conditions. First, we measured the turbidity decay as a function of pH. Figure 2a shows the decay curves obtained from these experiments. What is immediately notable is that pH has a strong influence on the formation and stability of the air bubbles. Figure 2b plots both decay times and maximum turbidity and shows that there is a peak in both observables at pH approximately 5.5. There is little bubble stabilization at acidic and basic pHs. Monomeric BslA in solution has an isoelectric point calculated to be 9.2. Therefore, it is curious that so little bubble stabilization occurs at basic pH (7–9). We ascribe this behaviour to a shift in the pI of BslA when bound to the air–water interface. Indeed, the pI of HFBII was found to shift when adsorbed to an air bubble . This pI change for adsorbed HFBII is thought to arise from the fact that a large proportion of the protein is no longer in contact with water, therefore only a fraction of the functional groups are ionizable. A shift in pI was also observed for emulsion films stabilized by β-lactoglobulin [32,33]. In this case, the shift was attributed to conformational changes that occur upon surface adsorption.Figure 2.
Affiliation: School of Physics and Astronomy, University of Edinburgh, James Clerk Maxwell Building, Peter Guthrie Tait Road, Edinburgh EH9 3FD, UK.