title: Protease homolog BepA (YfgC) promotes assembly and degradation of β-barrel membrane proteins in Escherichia coli.
abstract: Gram-negative bacteria are equipped with quality-control systems for the outer membrane (OM) that sense and cope with defective biogenesis of its components. Accumulation of misfolded outer membrane proteins (OMPs) in Escherichia coli leads to activation of σ(E), an essential alternative σ factor that up-regulates transcription of multiple genes required to preserve OM structure and function. Disruption of bepA (formerly yfgC), a σ(E)-regulated gene encoding a putative periplasmic metalloprotease, sensitizes cells to multiple drugs, suggesting that it may be involved in maintaining OM integrity. However, the specific function of BepA remains unclear. Here, we show that BepA enhances biogenesis of LptD, an essential OMP involved in OM transport and assembly of lipopolysaccharide, by promoting rearrangement of intramolecular disulfide bonds of LptD. In addition, BepA possesses protease activity and is responsible for the degradation of incorrectly folded LptD. In the absence of periplasmic chaperone SurA, BepA also promotes degradation of BamA, the central OMP subunit of the β-barrel assembly machinery (BAM) complex. Interestingly, defective oxidative folding of LptD caused by bepA disruption was partially suppressed by expression of protease-active site mutants of BepA, suggesting that BepA functions independently of its protease activity. We also show that BepA has genetic and physical interaction with components of the BAM complex. These findings raised the possibility that BepA maintains the integrity of OM both by promoting assembly of OMPs and by proteolytically eliminating OMPs when their correct assembly was compromised.
authors.affiliation: Institute for Virus Research, Kyoto University, Kyoto 606-8507, Japan.
authors.forename: Shin-ichiro
authors.initials: S
authors.lastname: Narita
authors.forename: Chigusa
authors.initials: C
authors.lastname: Masui
authors.forename: Takehiro
authors.initials: T
authors.lastname: Suzuki
authors.forename: Naoshi
authors.initials: N
authors.lastname: Dohmae
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Akiyama
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000096:biosynthesis* / Q000378:metabolism; D004926:Escherichia coli; D029968:Escherichia coli Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D047468:Immunoprecipitation; D045726:Metalloproteases / Q000235:genetics / Q000378:metabolism*; D033903:Periplasmic Proteins / Q000378:metabolism; D017510:Protein Folding; D059748:Proteolysis; D012808:Sigma Factor / Q000378:metabolism*
chemical_list: D001425:Bacterial Outer Membrane Proteins; C503914:BamA protein, E coli; D029968:Escherichia coli Proteins; C475958:LptD protein, E coli; D033903:Periplasmic Proteins; D012808:Sigma Factor; C063202:sporulation-specific sigma factors; C584537:BepA protein, E coli; D045726:Metalloproteases
keywords: disulfide bond formation; extracytoplasmic function sigma factor; peptidase M48; protein quality control; tetratricopeptide repeat (TPR) motif