Substrate selectivity of lysophospholipid transporter LplT involved in membrane phospholipid remodeling in Escherichia coli [Membrane Biology]

November 26th, 2015 by Lin, Y., Bogdanov, M., Tong, S., Guan, Z., Zheng, L.

Lysophospholipid transporter (LplT) was previously found to be primarily involved in 2-acyl lyso-PE recycling in gram-negative bacteria. This work identifies the potent role of LplT in maintaining membrane stability and integrity in the E.coli envelope. Here we demonstrate the involvement of LplT in the recycling of three major bacterial phospholipids using a combination of an in vitro lysophospholipid binding assay using purified protein and transport assays with E.coli spheroplasts. Our results show that lyso-PE and lyso-PG, but not lyso-PC, are taken up by LplT for reacylation by acyltransferase/acyl-ACP synthetase (Aas) on the inner leaflet of the membrane. We also found a novel cardiolipin hydrolysis reaction by phospholipase A2 to form diacylated cardiolipin progressing to the completely deacylated head group. These two distinct cardiolipin derivatives were both translocated with comparable efficiency to generate tri-acylated cardiolipin by Aas, demonstrating the first evidence of cardiolipin remodeling in bacteria. These findings support that a fatty acid chain is not required for LplT transport. We found that LplT cannot transport lyso-PA and its substrate binding was not inhibited by either orthophosphate or glycerol-3-phosphate, indicating that either a glycerol or ethanolamine head group is the chemical determinant for substrate recognition. Diacyl forms of PE, PG or the tetra-acylated form of cardiolipin could not serve as competitive inhibitor in vitro. Based on an evolutionary structural model, we propose a sideways sliding mechanism to explain how a conserved membrane-embedded α-helical interface excludes diacylphospholipids from the LplT binding site to facilitate efficient flipping of lysophospholipid across the cell membrane.
  • Posted in Journal of Biological Chemistry, Publications
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