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Membrane protein architects: the role of the BAM complex in outer membrane protein assembly

Nature Reviews Microbiology volume 7, pages 206–214 (2009)Cite this article

Key Points

  • The Gram-negative outer membrane protein (OMP) family includes proteins that are associated with basic physiological functions, virulence and multidrug resistance, and therefore plays a fundamental part in the maintenance of cellular viability.

  • Understanding how these proteins are targeted and folded into this membrane is crucial, as it could offer important medical benefits. Compounds that inhibit key stages of this process would block key stages of OMP biogenesis, thereby inhibiting essential physiological, pathogenic and drug resistance functions, and could prove useful in combating diverse pathogens, including Pseudomonas aeruginosa, Neisseria meningitidis and Salmonella enterica.

  • OMP biogenesis in Gram-negative bacteria has, until recently, remained a largely unknown mechanism. However, over the past 3 years, a complex of proteins has been discovered that is known as the β-barrel assembly machinery (BAM) and is responsible for folding and inserting OMPs into the membrane.

  • Recent advances in our understanding of the molecular basis of OMP biogenesis in Gram-negative bacteria are discussed.

  • Emphasis is placed on analysis of the recently discovered component structures and accessory interactions, in particular with the periplasmic chaperones DegP, Skp and SurA, which are known to interact with OMPs.

  • The mechanisms that the BAM complex might use in the folding and insertion of OMPs into the membrane are also discussed.

Abstract

The folding of transmembrane proteins into the outer membrane presents formidable challenges to Gram-negative bacteria. These proteins must migrate from the cytoplasm, through the inner membrane and into the periplasm, before being recognized by the β-barrel assembly machinery, which mediates efficient insertion of folded β-barrels into the outer membrane. Recent discoveries of component structures and accessory interactions of this complex are yielding insights into how cells fold membrane proteins. Here, we discuss how these structures illuminate the mechanisms responsible for the biogenesis of outer membrane proteins.

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Figure 1: Schematic representation of outer membrane protein biogenesis in Escherichia coli.
Figure 2: Structures of the outer membrane protein assembly components.
Figure 3: DegP cage structures.

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Authors and Affiliations

  1. Cancer Research UK Institute for Cancer Studies, School of Cancer Sciences, Edgbaston, B15 2TT, Birmingham, UK

    Timothy J. Knowles & Michael Overduin

  2. Division of Immunity and Infection, University of Birmingham, Edgbaston, B15 2TT, Birmingham, UK

    Anthony Scott-Tucker & Ian R. Henderson

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  1. Timothy J. Knowles
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  2. Anthony Scott-Tucker
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Correspondence to Ian R. Henderson.

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DATABASES

Entrez Genome Project

Bordetella pertussis

Drosophila melanogaster

Neisseria gonorrhoeae

Neisseria meningitidis

Pseudomonas aeruginosa

Salmonella enterica

Streptomyces clavuligeris

Xanthomonas axonopodis pathovar citri

Glossary

Chaperone

A protein that facilitates the proper folding of other proteins.

Amphipathic

A molecule with both polar and non-polar portions in its structure.

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Knowles, T., Scott-Tucker, A., Overduin, M. et al. Membrane protein architects: the role of the BAM complex in outer membrane protein assembly. Nat Rev Microbiol 7, 206–214 (2009). https://doi.org/10.1038/nrmicro2069

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