The outer membrane (OM) of Gram-negative bacteria such as Escherichia coli contains lipoproteins and integral β-barrel proteins (outer-membrane proteins, OMPs) assembled into an asymmetrical lipid bilayer. Insertion of β-barrel proteins into the OM is mediated by a protein complex that contains the OMP BamA and four associated lipoproteins (BamBCDE). The mechanism by which the Bam complex catalyzes the assembly of OMPs is not known. We report here the isolation and characterization of a temperature-sensitive lethal mutation, bamAE373K, which alters the fifth polypeptide transport-associated domain and disrupts the interaction between the BamAB and BamCDE subcomplexes. Suppressor mutations that map to codon 197 in bamD restore Bam complex function to wild-type levels. However, these suppressors do not restore the interaction betweenBamA and BamD; rather, they bypass the requirement for stable holocomplex formation by activating BamD. These results imply that BamA and BamD interact directly with OMP substrates.
|Number of pages
|Proceedings of the National Academy of Sciences of the United States of America
|Published - Feb 28 2012
All Science Journal Classification (ASJC) codes
- Conditional lethal
- Membrane protein folding