Interfacial self-assembly of a bacterial hydrophobin

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Bacteria in nature predominantly exist in biofilms.
• Bacillus subtilis biofilms are characterized by wrinkled morphology and hydrophobicity.
• The protein BslA is crucial for these biofilm properties, forming a surface coat.

Purpose of the Study:

• To elucidate the distinct mechanism of action for BslA in interfacial stabilization.
• To investigate the structural basis for BslA's function, comparing it to hydrophobins.
• To understand how BslA's structure responds to environmental interfaces.

Main Methods:

• Protein structure analysis (crystal structure of BslA).
• Biophysical techniques to study protein conformation and refolding at interfaces.
• Site-directed mutagenesis to probe the role of specific amino acids (e.g., leucine to lysine substitution).

Main Results:

• BslA possesses a large, surface-exposed hydrophobic patch, similar to hydrophobins, but lacks sequence/structural similarity.
• In aqueous solution, BslA's hydrophobic cap is shielded via a random coil conformation, ensuring solubility.
• At an interface, BslA refolds, exposing hydrophobic residues and forming a 2D rectangular lattice that stabilizes the interface.
• Mutating a key hydrophobic residue disrupted lattice formation and interfacial stabilization.

Conclusions:

• BslA employs a novel, environmentally responsive mechanism for interfacial stabilization distinct from hydrophobins.
• This mechanism involves a conformational change from a soluble random coil to an ordered, self-assembled structure at interfaces.
• BslA's structural plasticity is key to its role in Bacillus subtilis biofilm architecture and stability.