Inhibition of the β-barrel assembly machine by a peptide that binds BamD

The protein complex that assembles integral membrane beta-barrel proteins in the outer membranes of Gram-negative bacteria is an attractive target in the development of new antibiotics. This complex, the beta-barrel assembly machine (Bam), contains two essential proteins, BamA and BamD. We have identified a peptide that inhibits the assembly of beta-barrel proteins in vitro by characterizing the interaction of BamD with an unfolded substrate protein. This peptide is a fragment of the substrate protein and contains a conserved amino acid sequence. We have demonstrated that mutations of this sequence in the full-length substrate protein impair the protein's assembly, implying that BamD's interaction with this sequence is an important part of the assembly mechanism. Finally, we have found that in vivo expression of a peptide containing this sequence causes growth defects and sensitizes Escherichia coli to antibiotics to which they are normally resistant. Therefore, inhibiting the binding of substrates to BamD is a viable strategy for developing new antibiotics directed against Gram-negative bacteria.