Outer membrane β-barrel protein folding is physically controlled by periplasmic lipid head groups and BamA.
Outer membrane β-barrel proteins (OMPs) are crucial for numerous cellular processes in prokaryotes and eukaryotes. Despite extensive studies on OMP biogenesis, it is unclear why OMPs require assembly machineries to fold into their native outer membranes, as they are capable of folding quickly and efficiently through an intrinsic folding pathway in vitro. By investigating the folding of several bacterial OMPs using membranes with naturally occurring Escherichia coli lipids, we show that phosphoethanolamine and phosphoglycerol head groups impose a kinetic barrier to OMP folding. The kinetic retardation of OMP folding places a strong negative pressure against spontaneous incorporation of OMPs into inner bacterial membranes, which would dissipate the proton motive force and undoubtedly kill bacteria. We further show that prefolded β-barrel assembly machinery subunit A (BamA), the evolutionarily conserved, central subunit of the BAM complex, accelerates OMP folding by lowering the kinetic barrier imposed by phosphoethanolamine head groups. Our results suggest that OMP assembly machineries are required in vivo to enable physical control over the spontaneously occurring OMP folding reaction in the periplasm. Mechanistic studies further allowed us to derive a model for BamA function, which explains how OMP assembly can be conserved between prokaryotes and eukaryotes.
T. C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218.
Dennis
D
Gessmann
Yong Hee
YH
Chung
Emily J
EJ
Danoff
Ashlee M
AM
Plummer
Clifford W
CW
Sandlin
Nathan R
NR
Zaccai
Karen G
KG
Fleming
D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D055162:Biocatalysis; D002462:Cell Membrane / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D007700:Kinetics; D008055:Lipids / Q000737:chemistry*; D008954:Models, Biological; D019897:Periplasm / Q000378:metabolism*; D010649:Phenylalanine / Q000378:metabolism; D010714:Phosphatidylethanolamines / Q000378:metabolism; D010715:Phosphatidylglycerols / Q000378:metabolism; D017510:Protein Folding; D017433:Protein Structure, Secondary
D001425:Bacterial Outer Membrane Proteins; C503914:BamA protein, E coli; D029968:Escherichia coli Proteins; D008055:Lipids; D010714:Phosphatidylethanolamines; D010715:Phosphatidylglycerols; C483858:phosphatidylethanolamine; D010649:Phenylalanine
beta-barrel transmembrane protein; membrane protein folding