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Reconstitution of Outer Membrane Protein Assembly from Purified Components

Science  14 May 2010:
Vol. 328, Issue 5980, pp. 890-892
DOI: 10.1126/science.1188919

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Bring Out the β-Barrel

The assembly of β-barrel membrane proteins, which are found in the outer membrane of Gram-negative bacteria and in the mitochondria and chloroplasts of eukaryotes, is poorly understood. Now Hagan et al. (p. 890, published online 8 April; see the Perspective by Stroud et al.) describe the development of a reconstituted system that recapitulates the process of assembly of β-barrel membrane proteins by the Escherichia coli Bam complex. The assembly of a protein substrate required the purified five-protein Bam complex and several subcomplexes and a chaperone, but did not require an external input of energy.

Abstract

β-barrel membrane proteins in Gram-negative bacteria, mitochondria, and chloroplasts are assembled by highly conserved multi-protein complexes. The mechanism by which these molecular machines fold and insert their substrates is poorly understood. It has not been possible to dissect the folding and insertion pathway because the process has not been reproduced in a biochemical system. We purified the components that fold and insert Escherichia coli outer membrane proteins and reconstituted β-barrel protein assembly in proteoliposomes using the enzymatic activity of a protein substrate to report on its folding state. The assembly of this protein occurred without an energy source but required a soluble chaperone in addition to the multi-protein assembly complex.

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