title: Lysophospholipid flipping across the Escherichia coli inner membrane catalyzed by a transporter (LplT) belonging to the major facilitator superfamily.
abstract: The transfer of phospholipids across membrane bilayers is protein-mediated, and most of the established transporters catalyze the energy-dependent efflux of phospholipids from cells. This work identifies and characterizes a lysophospholipid transporter gene (lplT, formally ygeD) in Escherichia coli that is an integral component in the 2-acylglycerophosphoethanolamine (2-acyl-GPE) metabolic cycle for membrane protein acylation. The lplT gene is adjacent to and in the same operon as the aas gene, which encodes the bifunctional enzyme 2-acyl-GPE acyltransferase/acyl-acyl carrier protein synthetase. In some bacteria, acyltransferase/acyl-ACP synthetase (Aas) and LplT homologues are fused in a single polypeptide chain. 2-Acyl-GPE transport to the inside of the cell was assessed by measuring the Aas-dependent formation of phosphatidylethanolamine. The Aas-dependent incorporation of [3H]palmitate into phosphatidylethanolamine was significantly diminished in deltalplT mutants, and the LplT-Aas transport/acylation activity was independent of the proton motive force. The deltalplT mutants accumulated acyl-GPE in vivo and had a diminished capacity to transport exogenous 2-acylglycerophosphocholine into the cell. Spheroplasts prepared from wild-type E. coli transported and acylated fluorescent 2-acyl-GPE with an apparent K(d) of 7.5 microM, whereas this high-affinity process was absent in deltalplT mutants. Thus, LplT catalyzes the transbilayer movement of lysophospholipids and is the first example of a phospholipid flippase that belongs to the major facilitator superfamily.
authors.affiliation: Division of Biological Sciences, University of California at San Diego, La Jolla, California 92093-0116, USA.
authors.forename: Edgar M
authors.initials: EM
authors.lastname: Harvat
authors.forename: Yong-Mei
authors.initials: YM
authors.lastname: Zhang
authors.forename: Can V
authors.initials: CV
authors.lastname: Tran
authors.forename: Zhongge
authors.initials: Z
authors.lastname: Zhang
authors.forename: Matthew W
authors.initials: MW
authors.lastname: Frank
authors.forename: Charles O
authors.initials: CO
authors.lastname: Rock
authors.forename: Milton H
authors.initials: MH
authors.lastname: Saier
mesh_terms: D019730:Carbon-Sulfur Ligases / Q000502:physiology*; D002384:Catalysis; D002462:Cell Membrane / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000502:physiology*; D005227:Fatty Acids / Q000378:metabolism; D008051:Lipid Bilayers / Q000378:metabolism*; D008246:Lysophospholipids / Q000378:metabolism*; D049294:Phospholipid Transfer Proteins / Q000502:physiology*
chemical_list: D029968:Escherichia coli Proteins; D005227:Fatty Acids; D008051:Lipid Bilayers; C000608268:LplT protein, E coli; D008246:Lysophospholipids; D049294:Phospholipid Transfer Proteins; D019730:Carbon-Sulfur Ligases; C018749:long-chain-fatty-acid-(acyl-carrier-protein) ligase