Barn Lipoproteins Assemble BamA in Vitro

The Barn machine assembles beta-barrel membrane proteins into the outer membranes of Gram-negative bacteria. The central component of the Barn complex, BamA, is a beta-barrel that is conserved in prokaryotes and eukaryotes. We have previously reported an in vitro assay for studying the assembly of beta-barrel proteins by the Barn complex and now apply this assay to identify the specific components that are required for BamA assembly. We establish that BamB and BamD, two lipoprotein components of the complex, bind to the unfolded BamA substrate and are sufficient to accelerate its assembly into the membrane.