Structures of the β-barrel assembly machine recognizing outer membrane protein substrates.

Area of Science:

• Structural biology
• Molecular biology
• Biochemistry

Background:

• Beta-barrel outer membrane proteins (β-OMPs) are essential for Gram-negative bacteria.
• The β-barrel assembly machinery (BAM) complex facilitates β-OMP assembly.
• The precise mechanism of BAM-mediated assembly is not fully understood.

Purpose of the Study:

• To elucidate the structural mechanisms of the BAM complex during β-OMP assembly.
• To investigate the role of membrane environment and substrate interaction in BAM function.

Main Methods:

• X-ray crystallography to determine BAM complex structures in detergents and nanodisks.
• Structural analysis of BAM complex with bound β-OMP substrates.
• Functional analysis of substrate interactions.

Main Results:

• BAM complex structures reveal dynamic conformations modulated by membrane composition.
• Structures show the first β-strand of BamA (β1^BamA) interacting with the last β-strand of a β-OMP substrate.
• This interaction supports the β-signal hypothesis for β-OMP biogenesis.

Conclusions:

• The BAM complex is highly dynamic, with its conformation influenced by the surrounding membrane.
• The β1^BamA strand likely interacts with the terminal β-strand of incoming β-OMP substrates.
• This provides mechanistic insight into the initiation of β-OMP assembly.