Classifying β-Barrel Assembly Substrates by Manipulating Essential Bam Complex Members

Abstract

The outer membrane (OM) of Gram-negative bacteria, such as Escherichia coli, serves as a selective permeability barrier that prevents the uptake of toxic molecules and antibiotics. Integral β-barrel proteins (OMPs) are assembled by the β-barrel assembly machine (Bam), components of which are conserved in mitochondria, chloroplasts, and all Gram-negative bacteria, including many clinically relevant pathogenic species. Bam is essential for OM biogenesis and accommodates a diverse array of client proteins; however, a mechanistic model that accounts for the selectivity and broad substrate range of Bam is lacking. Here, we show that the assembly of multimeric OMPs is more strongly affected than that of monomeric OMPs when essential Bam complex components are limiting, suggesting that multiple Bam complexes are needed to assemble multimeric proteins.