Impact of holdase chaperones Skp and SurA on the folding of β-barrel outer-membrane proteins.
Chaperones increase the folding yields of soluble proteins by suppressing misfolding and aggregation, but how they modulate the folding of integral membrane proteins is not well understood. Here we use single-molecule force spectroscopy and NMR spectroscopy to observe the periplasmic holdase chaperones SurA and Skp shaping the folding trajectory of the large β-barrel outer-membrane receptor FhuA from Escherichia coli. Either chaperone prevents FhuA from misfolding by stabilizing a dynamic, unfolded state, thus allowing the substrate to search for structural intermediates. During this search, the SurA-chaperoned FhuA polypeptide inserts β-hairpins into the membrane in a stepwise manner until the β-barrel is folded. The membrane acts as a free-energy sink for β-hairpin insertion and physically separates transient folds from chaperones. This stabilization of dynamic unfolded states and the trapping of folding intermediates funnel the FhuA polypeptide toward the native conformation.
Department of Biosystems Science and Engineering, Eidgenössische Technische Hochschule Zürich, Basel, Switzerland.
Johannes
J
Thoma
Biozentrum, University of Basel, Basel, Switzerland.
Björn M
http://orcid.org/0000-0002-3135-7964
BM
Burmann
Biozentrum, University of Basel, Basel, Switzerland.
Sebastian
S
Hiller
Department of Biosystems Science and Engineering, Eidgenössische Technische Hochschule Zürich, Basel, Switzerland.
Daniel J
http://orcid.org/0000-0003-3075-0665
DJ
Müller
D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D001703:Biophysics; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D018625:Microscopy, Atomic Force; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000737:chemistry* / Q000378:metabolism*; D019696:Peptidylprolyl Isomerase / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D017510:Protein Folding; D013113:Spin Labels
D001425:Bacterial Outer Membrane Proteins; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C050900:FhuA protein, E coli; D018832:Molecular Chaperones; D013113:Spin Labels; C072721:Skp protein, E coli; C490900:SurA protein, E coli; D019696:Peptidylprolyl Isomerase