title: What's new with lactose permease.
abstract: The lactose permease of Escherichia coli is a paradigm for polytopic membrane transport proteins that transduce free energy stored in an electrochemical ion gradient into work in the form of a concentration gradient. Although the permease consists of 12 hydrophobic transmembrane domains in probable alpha-helical conformation that traverse the membrane in zigzag fashion connected by hydrophilic "loops", little information is available regarding the folded tertiary structure of the molecule. In a recent approach site-directed fluorescence labeling is being used to study proximity relationships in lactose permease. The experiments are based upon site-directed pyrene labeling of combinations of paired Cys replacements in a mutant devoid of Cys residues. Since pyrene exhibits excimer fluorescence if two molecules are within about 3.5A, the proximity between paired labeled residues can be determined. The results demonstrate that putative helices VIII and IX are close to helix X. Taken together with other findings indicating that helix VII is close to helices X and XI, the data lead to a model that describes the packing of helices VII to XI.
authors.affiliation: Howard Hughes Medical Institute, Department of Physiology, University of California Los Angeles 90024-1662.
authors.forename: H R
authors.initials: HR
authors.lastname: Kaback
authors.forename: K
authors.initials: K
authors.lastname: Jung
authors.forename: H
authors.initials: H
authors.lastname: Jung
authors.forename: J
authors.initials: J
authors.lastname: Wu
authors.forename: G G
authors.initials: GG
authors.lastname: Privé
authors.forename: K
authors.initials: K
authors.lastname: Zen
mesh_terms: D000595:Amino Acid Sequence; D001692:Biological Transport; D002462:Cell Membrane / Q000201:enzymology; D003545:Cysteine; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000378:metabolism*; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence; D027981:Symporters
chemical_list: D029968:Escherichia coli Proteins; C050221:LacY protein, E coli; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D027981:Symporters; C021499:lactose permease; D003545:Cysteine