The Bacterial Hydrophobin BslA is a Switchable Ellipsoidal Janus Nanocolloid

Abstract

BslA is an amphiphilic protein that forms a highly hydrophobic coat around Bacillus subtilis biofilms, shielding the bacterial community from external aqueous solution.It has a unique structure featuring a distinct partition between hydrophilic and hydrophobic surfaces. This surface property is reminiscent of synthesized Janus colloids.By investigating the behavior of BslA variants at water-cyclohexane interfaces through a set of multi-scale simulations informed by experimental data, we show that BslA indeed represents a biological example of an ellipsoidal Janus nanoparticle, whose surface * To whom correspondence should be addressed † School of Physics and Astronomy, University of Edinburgh ‡ Division of Molecular Microbiology, College of Life Sciences, University of Dundee ¶ Physics, School of Science and Engineering, University of Dundee § Computational Biology, School of Life Sciences, University of Dundee 1 interactions are, moreover, readily switchable. BslA contains a local conformational toggle, which controls its global affinity for, and orientation at, water-oil interfaces.This adaptability, together with single-point mutations, enables the fine-tuning of its solvent and interfacial interactions, and suggests that BslA could be a basis for biotechnological applications.

Bifunctionality of a biofilm matrix protein controlled by redox state

“…BslA is therefore multifunctional across three different axes: (i) Dimerization (and/or tetramerization) contributes to hydrophobicity, whereas monomeric protein is sufficient for biofilm complex architecture; (ii) the cap-out form of the protein renders a surface layer hydrophobic, whereas we can infer that a cap-in form is present in the wetting protein layer at the base of the biofilm where the protein is exposed to water (11,13); and (iii) stable lateral interactions between BslA molecules, which can be measured in vitro, appear to be required for architectural complexity, whereas unstable lateral interactions (reflected in unstable film formation in vitro) nonetheless are sufficient to give rise to hydrophobicity if dimeric protein is present. We have previously elucidated a link between the behavior of the cap region and the strength of lateral interactions (13), such that these two functionalities appear to influence each other.…”

“…We have previously elucidated a link between the behavior of the cap region and the strength of lateral interactions (13), such that these two functionalities appear to influence each other. Conversely, the behavior of the cap region of BslA is functionally independent from the protein oligomerization state, because both monomeric and dimeric protein are able to flip between cap-in and -out conformations.…”

“…The hydrophobicity of the biofilm has been attributed to a small secreted protein named BslA (7,8), which works alongside the fibrous protein TasA (9,10) and the extracellular polysaccharide produced by the products of the epsA-O operon (5) to allow morphogenesis of the biofilm. Partial evidence of the mechanism used by BslA to confer hydrophobicity to the B. subtilis biofilm has been revealed (8,(11)(12)(13). Although transcription of bslA occurs uniformly within the population, secreted BslA is localized to the periphery of the biofilm, where it forms a hydrophobic layer at the airbiofilm surface (8,12).…”

Influence of biofilm surface layer protein A (BslA) on the gel structure of myofibril protein from chicken breast

“…Therefore, BslA represents a good example of biological ellipsoidal Janus nanoparticles, whose unique feature of surface interaction is readily switchable (the word ‘switchable’ indicates here that BslA may change its state when protein adsorb or desorbs to the interface). In addition, BslA contains a local conformational toggle, which controls its affinity in water and oil interfaces . This adaptability, coupled with single point mutations, enables the fine tuning of its solvent and interfacial interactions.…”

“…In addition, BslA contains a local conformational toggle, which controls its affinity in water and oil interfaces. 12 This adaptability, coupled with single point mutations, enables the fine tuning of its solvent and interfacial interactions. These unique features of BslA attracted this study for its application in food science for the first time.…”