title: Reversible topological organization within a polytopic membrane protein is governed by a change in membrane phospholipid composition.
abstract: Once inserted, transmembrane segments of polytopic membrane proteins are generally considered stably oriented due to the large free energy barrier to topological reorientation of adjacent extramembrane domains. However, the topology and function of the polytopic membrane protein lactose permease of Escherichia coli are dependent on the membrane phospholipid composition, revealing topological dynamics of transmembrane domains after stable membrane insertion (Bogdanov, M., Heacock, P. N., and Dowhan, W. (2002) EMBO J. 21, 2107-2116). In this study, we show that the high affinity phenylalanine permease PheP shares many similarities with lactose permease. PheP assembled in a mutant of E. coli lacking phosphatidylethanolamine (PE) exhibited significantly reduced active transport function and a complete inversion in topological orientation of the N terminus and adjoining transmembrane hairpin loop compared with PheP in a PE-containing strain. Introduction of PE following the assembly of PheP triggered a reorientation of the N terminus and adjacent hairpin to their native orientation associated with regain of wild-type transport function. The reversible orientation of these secondary transport proteins in response to a change in phospholipid composition might be a result of inherent conformational flexibility necessary for transport function or during protein assembly.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Texas, Medical School, Houston, Texas 77030, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.forename: Mikhail
authors.initials: M
authors.lastname: Bogdanov
authors.forename: Jing
authors.initials: J
authors.lastname: Pi
authors.forename: A James
authors.initials: AJ
authors.lastname: Pittard
authors.forename: William
authors.initials: W
authors.lastname: Dowhan
mesh_terms: D026921:Amino Acid Transport Systems, Neutral / Q000737:chemistry*; D001426:Bacterial Proteins / Q000737:chemistry*; D001693:Biological Transport, Active; D015153:Blotting, Western; D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism; D003545:Cysteine / Q000737:chemistry; D004926:Escherichia coli / Q000201:enzymology; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins / Q000737:chemistry*; D008954:Models, Biological; D009004:Monosaccharide Transport Proteins; D009154:Mutation; D010649:Phenylalanine / Q000737:chemistry; D010714:Phosphatidylethanolamines / Q000737:chemistry; D010743:Phospholipids / Q000737:chemistry*; D011233:Precipitin Tests; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D027981:Symporters; D013997:Time Factors
chemical_list: D026921:Amino Acid Transport Systems, Neutral; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C050221:LacY protein, E coli; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D010714:Phosphatidylethanolamines; D010743:Phospholipids; D027981:Symporters; C069320:phenylalanine-specific permease, E coli; D010649:Phenylalanine; C021499:lactose permease; D003545:Cysteine