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Protein Sci. 2018 Feb;27(2):451-462. doi: 10.1002/pro.3337. Epub 2017 Nov 17.

Liprotides assist in folding of outer membrane proteins.

Author information

1
Department of Molecular Biology and Genetics, Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Aarhus C, DK, 8000, Denmark.
2
Department of Chemistry, Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Aarhus C, 8000, Denmark.

Abstract

Proteins and lipids can form complexes called liprotides, in which the partially denatured protein forms a shell encasing a lipid core. This effectively stabilizes a lipid micelle in an aqueous solvent and suggests that liprotides may provide a suitable vessel for membrane proteins. Accordingly we have investigated if liprotides consisting of α-lactalbumin and oleate could aid folding of four different outer membrane proteins (OMPs) tOmpA, PagP, BamA, and OmpF. tOmpA was able to fold in the presence of the liprotide, and folding did not occur if only oleate or α-lactalbumin were added. Although the liprotides did not fold the other three OMPs on its own, it was able to assist their folding in the presence of vesicles. Incubation with liprotides before folding into vesicles increased the folding yield of the outer membrane proteins to a level higher than using micelles of the non-ionic surfactant DDM. Even though the liprotide was stable at both high urea concentrations and high pH, it failed to efficiently fold OmpA at high pH. Instead, optimal folding was seen at pH 8-9, suggesting that important changes in the liprotide occurred when increasing the pH. We conclude that an otherwise folding-inactive fatty acid can be activated when presented by a liprotide and thereby work as an in vitro chaperone for outer membrane proteins.

KEYWORDS:

BamA; OmpF; PagP; chaperone; folding; liprotide; outer membrane proteins; tOmpA

PMID:
29094406
PMCID:
PMC5775180
[Available on 2019-02-01]
DOI:
10.1002/pro.3337

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