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Nat Chem Biol. 2015 Dec;11(12):981-7. doi: 10.1038/nchembio.1939. Epub 2015 Oct 19.

Mapping the energy landscape for second-stage folding of a single membrane protein.

Author information

1
National Creative Research Initiative Center for Single-Molecule Systems Biology, KAIST, Daejeon, South Korea.
2
Department of Physics, KAIST, Daejeon, South Korea.
3
Department of Chemistry and Biochemistry, University of California-Los Angeles, Los Angeles, California, USA.

Abstract

Membrane proteins are designed to fold and function in a lipid membrane, yet folding experiments within a native membrane environment are challenging to design. Here we show that single-molecule forced unfolding experiments can be adapted to study helical membrane protein folding under native-like bicelle conditions. Applying force using magnetic tweezers, we find that a transmembrane helix protein, Escherichia coli rhomboid protease GlpG, unfolds in a highly cooperative manner, largely unraveling as one physical unit in response to mechanical tension above 25 pN. Considerable hysteresis is observed, with refolding occurring only at forces below 5 pN. Characterizing the energy landscape reveals only modest thermodynamic stability (ΔG = 6.5 kBT) but a large unfolding barrier (21.3 kBT) that can maintain the protein in a folded state for long periods of time (t1/2 ∼3.5 h). The observed energy landscape may have evolved to limit the existence of troublesome partially unfolded states and impart rigidity to the structure.

PMID:
26479439
PMCID:
PMC4986997
DOI:
10.1038/nchembio.1939
[Indexed for MEDLINE]
Free PMC Article

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