Analysis of Transmembrane ß-Barrel Proteins by Native and Semi-native Polyacrylamide Gel Electrophoresis.

Membrane-embedded ß-barrel proteins are important regulators of the outer membrane permeability barrier of Gram-negative bacteria. ß-barrels are highly structured domains formed by a series of antiparallel ß-strands. Each ß-strand is locked in position by hydrogen bonds between its polypeptide backbone and those of the two neighbouring strands in the barrel structure. Some transmembrane ß-barrel proteins form larger homo- or hetero-multimeric complexes that accomplish specific functions. In this chapter, we describe native and semi-native polyacrylamide gel electrophoresis (PAGE) methods to characterize the organization of transmembrane ß-barrel proteins. We illustrate blue native (BN)-PAGE as an analytical method to assess the formation of protein complexes. Furthermore, we describe a heat-modifiability assay via semi-native PAGE as a rapid method to investigate the folding of transmembrane ß-barrels.

Lipoprotein DolP supports proper folding of BamA in the bacterial outer membrane promoting fitness upon envelope stress.

In Proteobacteria, integral outer membrane proteins (OMPs) are crucial for the maintenance of the envelope permeability barrier to some antibiotics and detergents. In Enterobacteria, envelope stress caused by unfolded OMPs activates the sigmaE (σE) transcriptional response. σE upregulates OMP biogenesis factors, including the ß-barrel assembly machinery (BAM) that catalyses OMP folding. Here we report that DolP (formerly YraP), a σE-upregulated and poorly understood outer membrane lipoprotein, is crucial for fitness in cells that undergo envelope stress. We demonstrate that DolP interacts with the BAM complex by associating with outer membrane-assembled BamA. We provide evidence that DolP is important for proper folding of BamA that overaccumulates in the outer membrane, thus supporting OMP biogenesis and envelope integrity. Notably, mid-cell recruitment of DolP had been linked to regulation of septal peptidoglycan remodelling by an unknown mechanism. We now reveal that, during envelope stress, DolP loses its association with the mid-cell, thereby suggesting a mechanistic link between envelope stress caused by impaired OMP biogenesis and the regulation of a late step of cell division.