Extreme Dynamics in the BamA β-Barrel Seam

Area of Science:

• Molecular biology
• Structural biology
• Biochemistry

Background:

• BamA (β-barrel assembly machine) is essential for outer membrane protein biogenesis in Gram-negative bacteria.
• BamA's β-barrel domain is proposed to catalyze outer membrane protein insertion and folding.
• Previous models suggested BamA's barrel seam acts as a lateral gate for nascent proteins.

Purpose of the Study:

• To investigate the role of BamA's barrel seam dynamics in outer membrane protein folding.
• To determine if locking the BamA barrel seam affects its catalytic activity.
• To elucidate the molecular mechanism of outer membrane protein insertion.

Main Methods:

• Disulfide locking and trapping experiments to analyze BamA barrel dynamics.
• Liposome-based assays to study the folding of a model outer membrane protein.
• Analysis of BamA barrel dynamics in both liposomes and the native Escherichia coli outer membrane.

Main Results:

• Disulfide locking of the BamA barrel did not impair its ability to fold a model outer membrane protein in liposomes.
• BamA's β-strands at the barrel seam showed significant "register sliding" dynamics (>14 Å) in liposomes.
• Similar extreme dynamics of the BamA barrel were observed in the native E. coli outer membrane.

Conclusions:

• BamA's barrel seam does not function as a static gate but is highly dynamic.
• These dynamics likely induce defects in the outer membrane, facilitating nascent outer membrane protein insertion.
• The findings challenge previous models and propose a new mechanism for outer membrane protein biogenesis involving BamA's inherent flexibility.