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J Biol Chem. 2018 Mar 2;293(9):3386-3398. doi: 10.1074/jbc.RA117.001231. Epub 2018 Jan 18.

The phospholipid-repair system LplT/Aas in Gram-negative bacteria protects the bacterial membrane envelope from host phospholipase A2 attack.

Author information

1
From the Center for Membrane Biology, Department of Biochemistry and Molecular Biology and.
2
the Departments of Biochemistry and Molecular Biology and.
3
the Department of Biochemistry, Duke University School of Medicine, Durham, North Carolina 27710, and.
4
Microbiology and Molecular Genetics, University of Texas McGovern Medical School, Houston, Texas 77030.
5
the Inflammation Program and Departments of Internal Medicine and Microbiology, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242.
6
From the Center for Membrane Biology, Department of Biochemistry and Molecular Biology and lei.zheng@uth.tmc.edu.

Abstract

Secretory phospholipases A2 (sPLA2s) are potent components of mammalian innate-immunity antibacterial mechanisms. sPLA2 enzymes attack bacteria by hydrolyzing bacterial membrane phospholipids, causing membrane disorganization and cell lysis. However, most Gram-negative bacteria are naturally resistant to sPLA2 Here we report a novel resistance mechanism to mammalian sPLA2 in Escherichia coli, mediated by a phospholipid repair system consisting of the lysophospholipid transporter LplT and the acyltransferase Aas in the cytoplasmic membrane. Mutation of the lplT or aas gene abolished bacterial lysophospholipid acylation activity and drastically increased bacterial susceptibility to the combined actions of inflammatory fluid components and sPLA2, resulting in bulk phospholipid degradation and loss of colony-forming ability. sPLA2-mediated hydrolysis of the three major bacterial phospholipids exhibited distinctive kinetics and deacylation of cardiolipin to its monoacyl-derivative closely paralleled bacterial death. Characterization of the membrane envelope in lplT- or aas-knockout mutant bacteria revealed reduced membrane packing and disruption of lipid asymmetry with more phosphatidylethanolamine present in the outer leaflet of the outer membrane. Moreover, modest accumulation of lysophospholipids in these mutant bacteria destabilized the inner membrane and rendered outer membrane-depleted spheroplasts much more sensitive to sPLA2 These findings indicated that LplT/Aas inactivation perturbs both the outer and inner membranes by bypassing bacterial membrane maintenance mechanisms to trigger specific interfacial activation of sPLA2 We conclude that the LplT/Aas system is important for maintaining the integrity of the membrane envelope in Gram-negative bacteria. Our insights may help inform new therapeutic strategies to enhance host sPLA2 antimicrobial activity.

KEYWORDS:

bacteria; bacterial resistance; lysophospholipid; membrane biogenesis; membrane envelope; membrane lipid; membrane structure; outer membrane asymmetry; phospholipase A; phospholipase A2; phospholipid turnover

PMID:
29348168
PMCID:
PMC5836115
DOI:
10.1074/jbc.RA117.001231
[Indexed for MEDLINE]
Free PMC Article

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