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Journal of Bioenergetics and... Dec 1993The lactose permease of Escherichia coli is a paradigm for polytopic membrane transport proteins that transduce free energy stored in an electrochemical ion gradient... (Review)
Review
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.
Topics: Amino Acid Sequence; Biological Transport; Cell Membrane; Cysteine; Escherichia coli; Escherichia coli Proteins; Membrane Transport Proteins; Molecular Sequence Data; Monosaccharide Transport Proteins; Mutagenesis, Site-Directed; Protein Conformation; Protein Structure, Secondary; Spectrometry, Fluorescence; Symporters
PubMed: 8144491
DOI: 10.1007/BF00770250 -
Sub-cellular Biochemistry 2019Transport of solutes across biological membranes is essential for cellular life. This process is mediated by membrane transport proteins which move nutrients, waste... (Review)
Review
Transport of solutes across biological membranes is essential for cellular life. This process is mediated by membrane transport proteins which move nutrients, waste products, certain drugs and ions into and out of cells. Secondary active transporters couple the transport of substrates against their concentration gradients with the transport of other solutes down their concentration gradients. The alternating access model of membrane transporters and the coupling mechanism of secondary active transporters are introduced in this book chapter. Structural studies have identified typical protein folds for transporters that we exemplify by the major facilitator superfamily (MFS) and LeuT folds. Finally, substrate binding and substrate translocation of the transporters LacY of the MFS and AdiC of the amino acid-polyamine-organocation (APC) superfamily are described.
Topics: Amino Acid Transport Systems; Biological Transport; Membrane Transport Proteins
PubMed: 31214990
DOI: 10.1007/978-3-030-18768-2_9 -
Biochimica Et Biophysica Acta Jul 1992
Review
Topics: Bacterial Proteins; Biological Transport; Chromosome Deletion; Escherichia coli; Escherichia coli Proteins; Genetic Complementation Test; Membrane Proteins; Membrane Transport Proteins; Monosaccharide Transport Proteins; Symporters
PubMed: 1633187
DOI: No ID Found -
Comptes Rendus Biologies Jun 2005More than 20% of the genes sequenced thus far appear to encode polytopic transmembrane proteins involved in a multitude of critical functions, particularly energy and... (Review)
Review
More than 20% of the genes sequenced thus far appear to encode polytopic transmembrane proteins involved in a multitude of critical functions, particularly energy and signal transduction. Many are important with regard to human disease (e.g., depression, diabetes, drug resistance), and many drugs are targeted to membrane transport proteins (e.g., fluoxetine and omeprazole). However, the number of crystal structures of membrane proteins, especially ion-coupled transporters, is very limited. Recently, an inward-facing conformer of the Escherichia coli lactose permease (LacY), a paradigm for the Major Facilitator Superfamily, which contains almost 4000 members, was solved at about 3.5 A in collaboration with Jeff Abramson and So Iwata at Imperial College London. This intensively studied membrane transport protein is composed of two pseudo-symmetrical 6-helix bundles with a large internal cavity containing bound sugar and open to the cytoplasm only. Based on the structure and a large body of biochemical and biophysical evidence, a mechanism is proposed in which the binding site is alternatively accessible to either side of the membrane.
Topics: Amino Acid Sequence; Binding Sites; Biological Transport; Escherichia coli; Escherichia coli Proteins; Membrane Transport Proteins; Models, Molecular; Molecular Sequence Data; Monosaccharide Transport Proteins; Protein Structure, Secondary; Protons; Symporters
PubMed: 15950162
DOI: 10.1016/j.crvi.2005.03.008 -
Research in Microbiology 1990The cellobiose (cel) operon of Escherichia coli was recently sequenced and shown to consist of five genes, celABCDF (Parker and Hall, 1990). We have shown that the CelA,... (Review)
Review
The cellobiose (cel) operon of Escherichia coli was recently sequenced and shown to consist of five genes, celABCDF (Parker and Hall, 1990). We have shown that the CelA, CelB and CelC proteins possess amino acid sequences which are homologous to different domains of the lactose permease of Staphylococcus aureus. CelB corresponds to the integral membrane portion of the permease (IIcel) while CelC (IIIcel) and CelA (IVcel) correspond to the two cytoplasmic domains which appear to comprise the first and second phosphorylation sites in the permease, respectively. The cellobiose permease is the only one of several homologous sequenced permeases of the phosphoenolpyruvate:sugar phosphotransferase system which has its three known functional domains residing on distinct polypeptide chains.
Topics: Amino Acid Sequence; Cellobiose; Escherichia coli; Lactose; Membrane Transport Proteins; Molecular Sequence Data; Sequence Alignment; Staphylococcus aureus
PubMed: 2092358
DOI: 10.1016/0923-2508(90)90079-6 -
Society of General Physiologists Series 1993
Review
Topics: Aspartic Acid; Cations, Monovalent; Escherichia coli; Glutamates; Glutamic Acid; Melibiose; Membrane Transport Proteins; Monosaccharide Transport Proteins; Mutation; Protein Conformation; Symporters
PubMed: 8099233
DOI: No ID Found -
Current Opinion in Structural Biology Aug 2004Structural knowledge of the major facilitator superfamily has dramatically increased during the past year with the emergence of the structures of three members of this... (Review)
Review
Structural knowledge of the major facilitator superfamily has dramatically increased during the past year with the emergence of the structures of three members of this family of transporters. All three structures reveal 12 transmembrane helices forming two distinct domains, and could imply that members of this superfamily have preserved both secondary and tertiary structure elements during evolution.
Topics: Binding Sites; Escherichia coli; Escherichia coli Proteins; Membrane Transport Proteins; Models, Molecular; Monosaccharide Transport Proteins; Protein Structure, Tertiary; Protein Transport; Structure-Activity Relationship; Substrate Specificity; Symporters
PubMed: 15313234
DOI: 10.1016/j.sbi.2004.07.005 -
Journal of Bacteriology Oct 1993Lactose permease mutants, which were previously isolated in sugar specificity studies, were screened for their abilities to transport the trisaccharide maltotriose. Six...
Lactose permease mutants, which were previously isolated in sugar specificity studies, were screened for their abilities to transport the trisaccharide maltotriose. Six multiple mutants (e.g., five double mutants and one triple mutant) were identified as forming fermentation-positive colonies on maltotriose MacConkey plates and were also shown to grow on maltotriose minimal plates. All of these multiple mutants contained a combination of two or three amino acid substitutions at position 177, 236, 306, or 322 within the permease. In contrast, none of the corresponding single mutants at these locations were observed to exhibit an enhanced rate of maltotriose transport. In whole-cell assays, the multiple mutants were shown to transport relatively long alpha-nitrophenylglucoside (alpha NPG) molecules. In certain cases, alpha NPG molecules containing up to four glucose residues in addition to the nitrophenyl group were shown to be transported to a significant degree. Overall, the abilities of lactose permease mutants to transport maltotriose and long alpha NPGs are discussed with regard to the dimensions of the sugar and the mechanism of sugar transport.
Topics: Biological Transport; Carbohydrate Sequence; Escherichia coli; Escherichia coli Proteins; Fermentation; Kinetics; Membrane Transport Proteins; Molecular Sequence Data; Monosaccharide Transport Proteins; Oligosaccharides; Plasmids; Point Mutation; Substrate Specificity; Symporters
PubMed: 8407799
DOI: 10.1128/jb.175.19.6269-6275.1993 -
Research in Microbiology 1990
Review
Topics: ATP-Binding Cassette Transporters; Adenosine Triphosphate; Amino Acid Transport Systems, Basic; Arsenates; Bacterial Proteins; Biological Transport, Active; Carbonyl Cyanide m-Chlorophenyl Hydrazone; Genes, Bacterial; Histidine; Maltose; Membrane Proteins; Membrane Transport Modulators; Membrane Transport Proteins; Models, Biological; Monosaccharide Transport Proteins; Proton-Translocating ATPases
PubMed: 2177913
DOI: 10.1016/0923-2508(90)90009-f -
Trends in Biochemical Sciences Aug 1990The polytopic membrane protein lac permease harnesses energy from the electrochemical H+ gradient to transport beta-galactosidases against a concentration gradient.... (Review)
Review
The polytopic membrane protein lac permease harnesses energy from the electrochemical H+ gradient to transport beta-galactosidases against a concentration gradient. Although high-resolution structural information is still lacking, the permease is thought to possess 12 membrane-spanning alpha-helical segments. Various experimental strategies, including site-directed mutagenesis, have been employed to probe the function of this membrane protein at the molecular level.
Topics: Amino Acid Sequence; Biological Transport; Escherichia coli; Escherichia coli Proteins; Galactosides; Glycosides; Membrane Transport Proteins; Molecular Sequence Data; Monosaccharide Transport Proteins; Symporters
PubMed: 2204157
DOI: 10.1016/0968-0004(90)90020-c