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Environment International May 2019Arsenic is a non-essential, environmentally ubiquitous toxic metalloid. In response to this pervasive environmental challenge, organisms evolved mechanisms to confer... (Review)
Review
Arsenic is a non-essential, environmentally ubiquitous toxic metalloid. In response to this pervasive environmental challenge, organisms evolved mechanisms to confer resistance to arsenicals. Inorganic pentavalent arsenate is taken into most cells adventitiously by phosphate uptake systems. Similarly, inorganic trivalent arsenite is taken into most cells adventitiously, primarily via aquaglyceroporins or sugar permeases. The most common strategy for tolerance to both inorganic and organic arsenicals is by efflux that extrude them from the cytosol. These efflux transporters span across kingdoms and belong to various families such as aquaglyceroporins, major facilitator superfamily (MFS) transporters, ATP-binding cassette (ABC) transporters and potentially novel, yet to be discovered families. This review will outline the properties and substrates of known arsenic transport systems, the current knowledge gaps in the field, and aims to provide insight into the importance of arsenic transport in the context of the global arsenic biogeocycle and human health.
Topics: Animals; Arsenic; Arsenicals; Biological Transport; Humans; Membrane Transport Proteins
PubMed: 30852446
DOI: 10.1016/j.envint.2019.02.058 -
Bacteriological Reviews Sep 1957
Topics: Bacteria; Enzymes; Membrane Transport Proteins; Osmosis; Permeability
PubMed: 13471457
DOI: 10.1128/br.21.3.169-194.1957 -
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 -
Proceedings of the National Academy of... Oct 2023Bacteria produce a structural layer of peptidoglycan (PG) that enforces cell shape, resists turgor pressure, and protects the cell. As bacteria grow and divide, the...
Bacteria produce a structural layer of peptidoglycan (PG) that enforces cell shape, resists turgor pressure, and protects the cell. As bacteria grow and divide, the existing layer of PG is remodeled and PG fragments are released. Enterics such as go to great lengths to internalize and reutilize PG fragments. is estimated to break down one-third of its cell wall, yet only loses ~0 to 5% of meso-diaminopimelic acid, a PG-specific amino acid, per generation. Two transporters were identified early on to possibly be the primary permease that facilitates PG fragment recycling, i) AmpG and ii) the Opp ATP binding cassette transporter in conjunction with a PG-specific periplasmic binding protein, MppA. The contribution of each transporter to PG recycling has been debated. Here, we have found that AmpG and MppA/Opp are differentially regulated by carbon source and growth phase. In addition, MppA/Opp is uniquely capable of high-affinity scavenging of muropeptides from growth media, demonstrating that AmpG and MppA/Opp allow for different strategies of recycling PG fragments. Altogether, this work clarifies environmental contexts under which utilizes distinct permeases for PG recycling and explores how scavenging by MppA/Opp could be beneficial in mixed communities.
Topics: Membrane Transport Proteins; Escherichia coli; Peptidoglycan; Bacterial Proteins; Bacteria; Cell Wall
PubMed: 37871219
DOI: 10.1073/pnas.2308940120 -
International Journal of Molecular... Mar 2021Active transport of sugars into bacteria occurs through symporters driven by ion gradients. is the most well-studied proton sugar symporter, whereas is the most... (Review)
Review
Active transport of sugars into bacteria occurs through symporters driven by ion gradients. is the most well-studied proton sugar symporter, whereas is the most characterized sodium sugar symporter. These are members of the major facilitator (MFS) and the amino acid-Polyamine organocation (APS) transporter superfamilies. While there is no structural homology between these transporters, they operate by a similar mechanism. They are nano-machines driven by their respective ion electrochemical potential gradients across the membrane. has 12 transmembrane helices (TMs) organized in two 6-TM bundles, each containing two 3-helix TM repeats. has a core structure of 10 TM helices organized in two inverted repeats (TM 1-5 and TM 6-10). In each case, a single sugar is bound in a central cavity and sugar selectivity is determined by hydrogen- and hydrophobic- bonding with side chains in the binding site. In vSGLT, the sodium-binding site is formed through coordination with carbonyl- and hydroxyl-oxygens from neighboring side chains, whereas in the proton (HO) site is thought to be a single glutamate residue (Glu325). The remaining challenge for both transporters is to determine how ion electrochemical potential gradients drive uphill sugar transport.
Topics: Binding Sites; Biological Transport, Active; Escherichia coli Proteins; Glucose; Lactose; Membrane Transport Proteins; Models, Molecular; Monosaccharide Transport Proteins; Protein Conformation; Sodium-Glucose Transport Proteins; Sugars; Symporters
PubMed: 33808202
DOI: 10.3390/ijms22073572 -
International Journal of Molecular... Oct 2018In over 40 years of research on the cellular uptake of auxin it is somewhat chastening that we have elaborated so little on the original kinetic descriptions of auxin... (Review)
Review
In over 40 years of research on the cellular uptake of auxin it is somewhat chastening that we have elaborated so little on the original kinetic descriptions of auxin uptake by plant cells made by Rubery and Sheldrake in 1974. Every aspect of that seminal work has been investigated in detail, and the uptake activity they measured is now known to be attributed to the AUX1/LAX family of permeases. Recent pharmacological studies have defined the substrate specificity of AUX1, biochemical studies have evaluated its permeability to auxin in plant cell membranes, and rigourous kinetic studies have confirmed the affinity of AUX1 for IAA and synthetic auxins. Advances in genome sequencing have provided a rich resource for informatic analysis of the ancestry of AUX1 and the LAX proteins and, along with models of topology, suggest mechanistic links to families of eukaryotic proton co-transporters for which crystal structures have been presented. The insights gained from all the accumulated research reflect the brilliance of Rubery and Sheldrake's early work, but recent biochemical analyses are starting to advance further our understanding of this vitally important family of auxin transport proteins.
Topics: Biological Transport, Active; Cell Membrane; Indoleacetic Acids; Membrane Transport Proteins; Plants
PubMed: 30380696
DOI: 10.3390/ijms19113391 -
Journal of Bacteriology Apr 2021Mycobacteria possess Mce transporters that import lipids and are thought to function analogously to ATP-binding cassette (ABC) transporters. However, whereas ABC...
Mycobacteria possess Mce transporters that import lipids and are thought to function analogously to ATP-binding cassette (ABC) transporters. However, whereas ABC transporters import substrates using a single solute-binding protein (SBP) to deliver a substrate to permease proteins in the membrane, mycobacterial Mce transporters have a potential for six SBPs (MceA to MceF) working with a pair of permeases (YrbEA and YrbEB), a cytoplasmic ATPase (MceG), and multiple Mce-associated membrane (Mam) and orphaned Mam (Omam) proteins to transport lipids. In this study, we used the model mycobacterium to study the requirement for individual Mce, Mam, and Omam proteins in Mce4 transport of cholesterol. All of the Mce4 and Mam4 proteins we investigated were required for cholesterol uptake. However, not all Omam proteins, which are encoded by genes outside loci, proved to contribute to cholesterol import. OmamA and OmamB were required for cholesterol import, while OmamC, OmamD, OmamE, and OmamF were not. In the absence of any single Mce4, Mam4, or Omam protein that we tested, the abundance of Mce4A and Mce4E declined. This relationship between the levels of Mce4A and Mce4E and these additional proteins suggests a network of interactions that assemble and/or stabilize a multiprotein Mce4 transporter complex. Further support for Mce transporters being multiprotein complexes was obtained by immunoprecipitation-mass spectrometry, in which we identified every single Mce, YrbE, MceG, Mam, and Omam protein with a role in cholesterol transport as associating with Mce4A. This study represents the first time any of these Mce4 transporter proteins has been shown to associate. How lipids travel between membranes of diderm bacteria is a challenging mechanistic question because lipids, which are hydrophobic molecules, must traverse a hydrophilic periplasm. This question is even more complex for mycobacteria, which have a unique cell envelope that is highly impermeable to molecules. A growing body of knowledge identifies Mce transporters as lipid importers for mycobacteria. Here, using protein stability experiments and immunoprecipitation-mass spectrometry, we provide evidence for mycobacterial Mce transporters existing as multiprotein complexes.
Topics: Adenosine Triphosphatases; Bacterial Proteins; Biological Transport; Cholesterol; Membrane Transport Proteins; Multiprotein Complexes; Mycobacterium smegmatis; Operon
PubMed: 33649150
DOI: 10.1128/JB.00685-20 -
Research in Microbiology 2019The transport of peptides in microorganisms plays an important role in their physiology and behavior, both as a nutrient source and as a proxy to sense their... (Review)
Review
The transport of peptides in microorganisms plays an important role in their physiology and behavior, both as a nutrient source and as a proxy to sense their environment. This latter function is evidenced in Gram-positive bacteria where cell-cell communication is mediated by small peptides. Here, we highlight the importance of the oligopeptide permease (Opp) systems in the various major processes controlled by signaling peptides, such as sporulation, virulence and conjugation. We underline that the functioning of these communication systems is tightly linked to the developmental status of the bacteria via the regulation of opp gene expression by transition phase regulators.
Topics: ATP-Binding Cassette Transporters; Bacterial Proteins; Biological Transport; Gene Expression Regulation, Bacterial; Gram-Positive Bacteria; Membrane Transport Proteins; Peptide Termination Factors; Quorum Sensing; Signal Transduction
PubMed: 31376485
DOI: 10.1016/j.resmic.2019.07.004 -
Proceedings of the National Academy of... May 1997
Review
Topics: Amino Acid Sequence; Bacteria; Bacteriorhodopsins; Biological Transport, Active; Carrier Proteins; Cell Membrane; Escherichia coli; Escherichia coli Proteins; Membrane Transport Proteins; Monosaccharide Transport Proteins; Symporters
PubMed: 9159101
DOI: 10.1073/pnas.94.11.5508 -
Scientific Reports Sep 2018The sugar transporter Lactose permease (LacY) of Escherichia coli has become a prototype to understand the underlying molecular details of membrane transport. Crystal...
The sugar transporter Lactose permease (LacY) of Escherichia coli has become a prototype to understand the underlying molecular details of membrane transport. Crystal structures have trapped the protein in sugar-bound states facing the periplasm, but with narrow openings unable to accommodate sugar. Therefore, the molecular details of sugar uptake remain elusive. In this work, we have used extended simulations and metadynamics sampling to explore a putative sugar-uptake pathway and associated free energy landscape. We found an entrance at helix-pair 2 and 11, which involved lipid head groups and residues Gln 241 and Gln 359. Furthermore, the protein displayed high flexibility on the periplasmic side of Phe 27, which is located at the narrowest section of the pathway. Interactions to Phe 27 enabled passage into the binding site, which was associated with a 24 ± 4 kJ/mol binding free energy in excellent agreement with an independent binding free energy calculation and experimental data. Two free energy minima corresponding to the two possible binding poses of the lactose analog β-D-galactopyranosyl-1-thio-β-D-galactopyranoside (TDG) were aligned with the crystal structure-binding pocket. This work outlines the chemical environment of a putative periplasmic sugar pathway and paves way for understanding substrate affinity and specificity in LacY.
Topics: Cell Membrane; Lipid Bilayers; Membrane Transport Proteins; Molecular Dynamics Simulation; Periplasm; Protein Conformation; Protein Transport; Thermodynamics
PubMed: 30254312
DOI: 10.1038/s41598-018-32624-7