Dataset Information

Extreme Dynamics in the BamA ?-Barrel Seam.

ABSTRACT: BamA is an essential component of the ?-barrel assembly machine (BAM) that is responsible for insertion and folding of ?-barrel outer membrane proteins (OMPs) in Gram-negative bacteria. BamA is an OMP itself, and its ?-barrel transmembrane domain is thought to catalyze OMP insertion and folding, although the molecular mechanism remains poorly understood. Crystal structures of BamA and complementary molecular dynamics simulations have shown that its ?-barrel seam (the interface between the first and last barrel strands) is destabilized. This has led to mechanistic models in which the BamA barrel seam functions as a lateral gate that opens and successively accepts ?-hairpins from a nascent OMP such that a nascent barrel can bud from BamA. Consistent with this model, disulfide locking of the BamA barrel seam is lethal in Escherichia coli. Here we show that disulfide locking of the BamA barrel has no effect on its ability to catalyze folding of a model OMP into liposomes. However, disulfide trapping experiments indicate that the BamA barrel is highly dynamic in the liposome membranes, with the ?-strands at the barrel seam undergoing "register sliding" by more than 14 Å both up and down the membrane. Remarkably, these extreme dynamics were also observed in the BamA barrel in the context of the native E. coli outer membrane. These results are consistent with a model in which the BamA barrel dynamics induce defects in the outer membrane that facilitate insertion of nascent OMPs.

SUBMITTER: Doerner PA

PROVIDER: S-EPMC5995120 | biostudies-literature | 2017 Jun

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Extreme Dynamics in the BamA β-Barrel Seam.

Doerner Pamela Arden PA Sousa Marcelo C MC

Biochemistry 20170612 24

BamA is an essential component of the β-barrel assembly machine (BAM) that is responsible for insertion and folding of β-barrel outer membrane proteins (OMPs) in Gram-negative bacteria. BamA is an OMP itself, and its β-barrel transmembrane domain is thought to catalyze OMP insertion and folding, although the molecular mechanism remains poorly understood. Crystal structures of BamA and complementary molecular dynamics simulations have shown that its β-barrel seam (the interface between the first ...[more]

PMID: 28569500

Similar Datasets

Project description:Most integral outer membrane proteins (OMPs) of Gram-negative bacteria, such as Escherichia coli, assume a β-barrel structure. The β-barrel assembly machine (Bam), a five-member complex composed of β-barrel OMP BamA and four associated lipoproteins, BamB, BamC, BamD, and BamE, folds and inserts OMPs into the outer membrane. The two essential proteins BamA and BamD interact to stabilize two subcomplexes, BamAB and BamCDE, and genetic and structural evidence suggests that interactions between BamA and BamD occur via an electrostatic interaction between a conserved aspartate residue in a periplasmic domain of BamA and a conserved arginine in BamD. In this work, we characterize charge-change mutations at these key BamA and BamD residues and nearby charged residues in BamA with respect to OMP assembly and Bam complex stability. We show that Bam complex stability does not correlate with function, that BamA and BamD must adopt at least two active conformational states during OMP assembly, and that these charged residues are not required for function. Rather, these charged residues are important for coordinating the activities of BamA and BamD to allow efficient OMP assembly. We present a model of OMP assembly wherein recognition and binding of unfolded OMP substrate by BamA and BamD induce a signaling interaction between the two proteins, causing conformational changes necessary for the assembly reaction to proceed. By analogy to signal sequence recognition by SecYEG, we believe these BamA-BamD interactions ensure that both substrate and complex are competent for OMP assembly before the assembly reaction commences.IMPORTANCE Conformational changes in the proteins of the β-barrel assembly machine (Bam complex) are associated with the folding and assembly of outer membrane proteins (OMPs) in Gram-negative bacteria. We show that electrostatic interactions between the two essential proteins BamA and BamD coordinate conformational changes upon binding of unfolded substrate that allow the assembly reaction to proceed. Mutations affecting this interaction are lethal not because they destabilize the Bam complex but rather because they disrupt this coordination. Our model of BamA-BamD interactions regulating conformation in response to proper substrate interaction is reminiscent of conformational changes the secretory (Sec) machinery undergoes after signal sequence recognition that ensure protein quality control.

Dataset Information

Extreme Dynamics in the BamA ?-Barrel Seam.

Publications

Extreme Dynamics in the BamA β-Barrel Seam.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets