Defining key roles for auxiliary proteins in an ABC transporter that maintains bacterial outer membrane lipid asymmetry
- National University of Singapore, Singapore
Abstract
In Gram-negative bacteria, lipid asymmetry is critical for the function of the outer membrane (OM) as a selective permeability barrier, but how it is established and maintained is poorly understood. Here, we characterize a non-canonical ATP-binding cassette (ABC) transporter in Escherichia coli that provides energy for maintaining OM lipid asymmetry via the transport of aberrantly localized phospholipids (PLs) from the OM to the inner membrane (IM). We establish that the transporter comprises canonical components, MlaF and MlaE, and auxiliary proteins, MlaD and MlaB, of previously unknown functions. We further demonstrate that MlaD forms extremely stable hexamers within the complex, functions in substrate binding with strong affinity for PLs, and modulates ATP hydrolytic activity. In addition, MlaB plays critical roles in both the assembly and activity of the transporter. Our work provides mechanistic insights into how the MlaFEDB complex participates in ensuring active retrograde PL transport to maintain OM lipid asymmetry.
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Author details
Funding
National University of Singapore (Start-up funding)
- Shu-Sin Chng
Ministry of Education - Singapore (Academic Research fund Tier 2 (MOE2013-T2-1-148))
- Shu-Sin Chng
National Research Foundation Singapore (NRFI2015-05)
- Markus R Wenk
Agency for Science, Technology and Research (BMRC-SERC 112 148 0006)
- Markus R Wenk
National University of Singapore (Life Science Institute)
- Markus R Wenk
Ministry of Education - Singapore (Academic Research Fund Tier 1)
- Shu-Sin Chng
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Copyright
© 2016, Thong et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Defining key roles for auxiliary proteins in an ABC transporter that maintains bacterial outer membrane lipid asymmetry
eLife 5:e19042.
https://doi.org/10.7554/eLife.19042
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