title: Interfacial self-assembly of a bacterial hydrophobin.
abstract: The majority of bacteria in the natural environment live within the confines of a biofilm. The Gram-positive bacterium Bacillus subtilis forms biofilms that exhibit a characteristic wrinkled morphology and a highly hydrophobic surface. A critical component in generating these properties is the protein BslA, which forms a coat across the surface of the sessile community. We recently reported the structure of BslA, and noted the presence of a large surface-exposed hydrophobic patch. Such surface patches are also observed in the class of surface-active proteins known as hydrophobins, and are thought to mediate their interfacial activity. However, although functionally related to the hydrophobins, BslA shares no sequence nor structural similarity, and here we show that the mechanism of action is also distinct. Specifically, our results suggest that the amino acids making up the large, surface-exposed hydrophobic cap in the crystal structure are shielded in aqueous solution by adopting a random coil conformation, enabling the protein to be soluble and monomeric. At an interface, these cap residues refold, inserting the hydrophobic side chains into the air or oil phase and forming a three-stranded β-sheet. This form then self-assembles into a well-ordered 2D rectangular lattice that stabilizes the interface. By replacing a hydrophobic leucine in the center of the cap with a positively charged lysine, we changed the energetics of adsorption and disrupted the formation of the 2D lattice. This limited structural metamorphosis represents a previously unidentified environmentally responsive mechanism for interfacial stabilization by proteins.
authors: School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom;
authors: Keith M
authors: KM
authors: Bromley
authors: School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom;
authors: Ryan J
authors: RJ
authors: Morris
authors: Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom; and.
authors: Laura
authors: L
authors: Hobley
authors: School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom;
authors: Giovanni
authors: G
authors: Brandani
authors: Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom; and.
authors: Rachel M C
authors: RM
authors: Gillespie
authors: School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom;
authors: Matthew
authors: M
authors: McCluskey
authors: Division of Computational Biology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom.
authors: Ulrich
authors: U
authors: Zachariae
authors: School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom;
authors: Davide
authors: D
authors: Marenduzzo
authors: Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom; and cait.macphee@ed.ac.uk n.r.stanleywall@dundee.ac.uk.
authors: Nicola R
authors: NR
authors: Stanley-Wall
authors: School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom; cait.macphee@ed.ac.uk n.r.stanleywall@dundee.ac.uk.
authors: Cait E
authors: CE
authors: MacPhee
mesh_terms: D001412:Bacillus subtilis / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D055550:Protein Stability; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
chemical_list: D001426:Bacterial Proteins
keywords: Bacillus subtilis; BslA; bacterial hydrophobin; biofilm; interfacial self-assembly