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Mol Microbiol. 2017 Oct;106(1):142-156. doi: 10.1111/mmi.13757. Epub 2017 Aug 9.

Structural basis for substrate selection by the translocation and assembly module of the β-barrel assembly machinery.

Author information

1
Infection & Immunity Program, Biomedicine Discovery Institute and Department of Microbiology, Monash University, Clayton, VIC 3800, Australia.
2
School of Physics, Georgia Institute of Technology, Atlanta, GA 30332, USA.
3
School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.
4
Monash Biomedical Proteomics Facility, Biomedicine Discovery Institute and Department of Biochemistry & Molecular Biology, Monash University, Clayton, VIC 3800, Australia.
5
Medical Biochemistry and Molecular Biology, Saarland University, Homburg 66421, Germany.

Abstract

The assembly of proteins into bacterial outer membranes is a key cellular process that we are only beginning to understand, mediated by the β-barrel assembly machinery (BAM). Two crucial elements of that machinery are the core BAM complex and the translocation and assembly module (TAM), with each containing a member of the Omp85 superfamily of proteins: BamA in the BAM complex, TamA in the TAM. Here, we used the substrate protein FimD as a model to assess the selectivity of substrate interactions for the TAM relative to those of the BAM complex. A peptide scan revealed that TamA and BamA bind the β-strands of FimD, and do so selectively. Chemical cross-linking and molecular dynamics are consistent with this interaction taking place between the first and last strand of the TamA barrel domain, providing the first experimental evidence of a lateral gate in TamA: a structural element implicated in membrane protein assembly. We suggest that the lateral gates in TamA and BamA provide different environments for substrates to engage, with the differences observed here beginning to address how the TAM can be more effective than the BAM complex in the folding of some substrate proteins.

PMID:
28752534
PMCID:
PMC5607099
DOI:
10.1111/mmi.13757
[Indexed for MEDLINE]
Free PMC Article

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