title: Phospholipids as determinants of membrane protein topology. Phosphatidylethanolamine is required for the proper topological organization of the gamma-aminobutyric acid permease (GabP) of Escherichia coli.
abstract: Evidence is accumulating that the topological organization and hence function of some membrane proteins are not solely determined by the amino acid sequence of the protein but are also influenced by the lipid composition of the membrane. The gamma-aminobutyric acid (GABA) permease (GabP) of Escherichia coli has been found in this study to be affected both topologically and kinetically by membrane lipids. Using single cysteine accessibility methods with viable E. coli strains of natural lipid composition and those lacking phosphatidylethanolamine (PE), we have shown that the N-terminal hairpin of GabP is inverted relative to the membrane in PE-lacking cells, with a hinge point in transmembrane domain III. The rate of GABA transport is reduced by more than 99% in PE-lacking cells. The Michaelis constant for GABA transport is not greatly affected nor is the dependence of transport on energy. However, "transport specificity ratio" analysis demonstrated a clear transition state stability difference for GABA and nipecotic acid between the protein in PE-containing and PE-lacking cells. The patterns of observed effects are similar to those seen with the phenylalanine transporter of E. coli (Zhang, W., Bogdanov, M. Pi, J. Pittard, A. J., and Dowhan, W. (2003) J. Biol. Chem. 278, 50128-50135), also an amino acid/polyamine/organocation family member but quite distinct from those observed with lactose permease (Bogdanov, M., Heacock, P. N., and Dowhan, W. (2002) EMBO J. 21, 2107-2116), a major facilitator superfamily member. Therefore, by extending the studies of similarities and differences in lipid responses among and between family groups, we may identify elements within the proteins that facilitate lipid responsiveness.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Texas-Houston, Medical School and Graduate School of Biomedical Sciences, Houston, Texas 77030, USA. weiz@stanford.edu
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.forename: Heidi A
authors.initials: HA
authors.lastname: Campbell
authors.forename: Steven C
authors.initials: SC
authors.lastname: King
authors.forename: William
authors.initials: W
authors.lastname: Dowhan
mesh_terms: D001667:Binding, Competitive; D001692:Biological Transport; D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism*; D018360:Crystallography, X-Ray; D003545:Cysteine / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D050485:GABA Plasma Membrane Transport Proteins; D047468:Immunoprecipitation; D007700:Kinetics; D050356:Lipid Metabolism; D008055:Lipids / Q000737:chemistry; D026901:Membrane Transport Proteins / Q000378:metabolism; D008954:Models, Biological; D027361:Organic Anion Transporters / Q000378:metabolism / Q000502:physiology*; D010649:Phenylalanine / Q000737:chemistry; D010714:Phosphatidylethanolamines / Q000737:chemistry / Q000378:metabolism*; D010743:Phospholipids / Q000737:chemistry / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013997:Time Factors
chemical_list: D029968:Escherichia coli Proteins; D050485:GABA Plasma Membrane Transport Proteins; D008055:Lipids; D026901:Membrane Transport Proteins; D027361:Organic Anion Transporters; D010714:Phosphatidylethanolamines; D010743:Phospholipids; C513601:gabP protein, E coli; C483858:phosphatidylethanolamine; D010649:Phenylalanine; C021499:lactose permease; D003545:Cysteine