title: Ligand-induced changes in periplasmic loops in the lactose permease of Escherichia coli.
abstract: N- and C-terminal halves of lactose permease, each with a single-Cys residue in a periplasmic loop, were coexpressed, and cross-linking was studied in the presence or absence of ligand. A Cys residue at position 36 between transmembrane helices I and II (loop I/II) forms a disulfide spontaneously with a Cys residue at position 253, 254, 255, or 256 in loop VII/VIII. Moreover, in the presence of o-phenanthroline-copper, a Cys residue at position 42 in loop I/II forms a disulfide with a Cys residue at position 253, 254, 257, or 258 in loop VII/VIII. Changes in the rate of cross-linking are also observed in the presence of substrate, suggesting that ligand binding induces movement between loops I/II and VII/VIII such that positions 253-256 are brought closer to position 36 or 42, while positions 257 and 258 move away from position 42.
authors.affiliation: Howard Hughes Medical Institute, Department of Physiology, University of California, Los Angeles 90095-1662, USA.
authors.forename: J
authors.initials: J
authors.lastname: Sun
authors.forename: C R
authors.initials: CR
authors.lastname: Kemp
authors.forename: H R
authors.initials: HR
authors.lastname: Kaback
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D001692:Biological Transport; D003432:Cross-Linking Reagents; D003545:Cysteine / Q000235:genetics; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins; D005816:Genetic Complementation Test; D008024:Ligands; D008301:Maleimides; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics; D009004:Monosaccharide Transport Proteins; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics; D017433:Protein Structure, Secondary; D027981:Symporters; D013862:Thiogalactosides
chemical_list: D003432:Cross-Linking Reagents; D029968:Escherichia coli Proteins; C050221:LacY protein, E coli; D008024:Ligands; D008301:Maleimides; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D010446:Peptide Fragments; D027981:Symporters; D013862:Thiogalactosides; C075594:1,6-bismaleimidohexane; C031803:thiodigalactoside; C021499:lactose permease; D003545:Cysteine