scholarly journals Unique structural features in an Nramp metal transporter impart substrate-specific proton cotransport and a kinetic bias to favor import

2019 ◽  
Vol 151 (12) ◽  
pp. 1413-1429 ◽  
Author(s):  
Aaron T. Bozzi ◽  
Lukas B. Bane ◽  
Christina M. Zimanyi ◽  
Rachelle Gaudet
Keyword(s):  
Proton Transport ◽  
Metal Uptake ◽  
Deinococcus Radiodurans ◽  
Salt Bridge ◽  
Metal Transport ◽  
Natural Resistance ◽  
Transport Pathway ◽  
Directional Bias ◽  
Proton Cotransport ◽  
Stimulation Of

Natural resistance-associated macrophage protein (Nramp) transporters enable uptake of essential transition metal micronutrients in numerous biological contexts. These proteins are believed to function as secondary transporters that harness the electrochemical energy of proton gradients by “coupling” proton and metal transport. Here we use the Deinococcus radiodurans (Dra) Nramp homologue, for which we have determined crystal structures in multiple conformations, to investigate mechanistic details of metal and proton transport. We untangle the proton-metal coupling behavior of DraNramp into two distinct phenomena: ΔpH stimulation of metal transport rates and metal stimulation of proton transport. Surprisingly, metal type influences substrate stoichiometry, leading to manganese-proton cotransport but cadmium uniport, while proton uniport also occurs. Additionally, a physiological negative membrane potential is required for high-affinity metal uptake. To begin to understand how Nramp’s structure imparts these properties, we target a conserved salt-bridge network that forms a proton-transport pathway from the metal-binding site to the cytosol. Mutations to this network diminish voltage and ΔpH dependence of metal transport rates, alter substrate selectivity, perturb or eliminate metal-stimulated proton transport, and erode the directional bias favoring outward-to-inward metal transport under physiological-like conditions. Thus, this unique salt-bridge network may help Nramp-family transporters maximize metal uptake and reduce deleterious back-transport of acquired metals. We provide a new mechanistic model for Nramp proton-metal cotransport and propose that functional advantages may arise from deviations from the traditional model of symport.

scholarly journals Transmembrane helix 6b links proton- and metal-release pathways to drive conformational change in an Nramp transition metal transporter

2019 ◽  
Author(s):  
Aaron T. Bozzi ◽  
Anne L. McCabe ◽  
Benjamin C. Barnett ◽  
Rachelle Gaudet
Keyword(s):  
Transition Metal ◽  
Conformational Change ◽  
Metal Binding ◽  
Deinococcus Radiodurans ◽  
Transmembrane Helix ◽  
Metal Transport ◽  
Natural Resistance ◽  
Metal Release ◽  
Transport Pathway ◽  
Exit Route

ABSTRACTThe natural resistance-associated macrophage protein (Nramp) family encompasses transition metal and proton co-transporters found in organisms from bacteria to humans. Recent structures ofDeinococcus radiodurans(Dra)Nramp in multiple conformations revealed the intramolecular rearrangements required for alternating access. Here we demonstrate that two parallel cytoplasm-accessible networks of conserved hydrophilic residues in DraNramp—one lining the wide intracellular vestibule for metal release, the other forming a narrow proton-transport pathway—are essential for metal transport. We further show that mutagenic or post-translational modifications of transmembrane helix (TM) 6b, which structurally links these two pathways, impedes normal conformational cycling and metal transport. TM6b contains two highly conserved histidines, H232 and H237. Different mutagenic perturbations for H232, just below the metal-binding site along the proton-exit route, differentially affect DraNramp’s conformational state, suggesting H232 serves as a pivot point for conformational change. In contrast, any tested replacement for H237, lining the metal-exit route, locks the transporter in a transport-inactive outward-closed state. We conclude that these two histidines, and TM6b more broadly, help trigger the bulk rearrangement to the inward-open state upon metal binding and facilitate the return of the empty transporter to an outward-open state upon metal release.

scholarly journals Proton co-transport and voltage dependence enforce unidirectional metal transport in an Nramp transporter

2018 ◽  
Author(s):  
Aaron T. Bozzi ◽  
Lukas B. Bane ◽  
Christina M. Zimanyi ◽  
Rachelle Gaudet
Keyword(s):  
Metal Binding ◽  
Voltage Dependence ◽  
Mechanistic Model ◽  
Salt Bridge ◽  
Metal Transport ◽  
Natural Resistance ◽  
Metal Type ◽  
Proton Symport ◽  
Macrophage Protein ◽  
Stimulation Of

AbstractSecondary transporters harness electrochemical energy to move substrate through structurally-enforced co-substrate “coupling”. We untangle the “proton-metal coupling” behavior by a Natural resistance-associated macrophage protein (Nramp) transporter into two distinct phenomena: ΔpH stimulation of metal transport and metal stimulation of proton co-transport. Surprisingly, metal type dictates co-transport stoichiometry, leading to manganese-proton symport but cadmium uniport. Additionally, the membrane potential affects both the kinetics and thermodynamics of metal transport. A conserved salt-bridge network near the metal-binding site imparts voltage dependence and enables proton co-transport, properties that allow this Nramp transporter to maximize metal uptake and prevent deleterious back-transport of acquired metals. We provide a new mechanistic model for Nramp metal-proton symport in which, in addition to substrate gradients determining directionality as in canonical secondary transport, synergy between protein structure and physiological voltage enforces unidirectional substrate movement. Our results illustrate a functional advantage that arises from deviations from the traditional model of symport.

scholarly journals Transmembrane helix 6b links proton and metal release pathways and drives conformational change in an Nramp-family transition metal transporter

2019 ◽  
Vol 295 (5) ◽  
pp. 1212-1224 ◽  
Author(s):  
Aaron T. Bozzi ◽  
Anne L. McCabe ◽  
Benjamin C. Barnett ◽  
Rachelle Gaudet
Keyword(s):  
Transition Metal ◽  
Binding Site ◽  
Metal Binding ◽  
Transmembrane Helix ◽  
Metal Transport ◽  
Natural Resistance ◽  
Metal Release ◽  
Transport Pathway ◽  
Metal Binding Site ◽  
Exit Route

The natural resistance-associated macrophage protein (Nramp) family encompasses transition metal and proton cotransporters that are present in many organisms from bacteria to humans. Recent structures of Deinococcus radiodurans Nramp (DraNramp) in multiple conformations revealed the intramolecular rearrangements required for alternating access of the metal-binding site to the external or cytosolic environment. Here, using recombinant proteins and metal transport and cysteine accessibility assays, we demonstrate that two parallel cytoplasm-accessible networks of conserved hydrophilic residues in DraNramp, one lining the wide intracellular vestibule for metal release and the other forming a narrow proton transport pathway, are essential for metal transport. We further show that mutagenic or posttranslational modifications of transmembrane helix (TM) 6b, which structurally links these two pathways, impede normal conformational cycling and metal transport. TM6b contains two highly conserved histidines, His232 and His237. We found that different mutagenic perturbations of His232, just below the metal-binding site along the proton exit route, differentially affect DraNramp's conformational state, suggesting that His232 serves as a pivot point for conformational changes. In contrast, any replacement of His237, lining the metal exit route, locked the transporter in a transport-inactive outward-closed state. We conclude that these two histidines, and TM6b more broadly, help trigger the bulk rearrangement of DraNramp to the inward-open state upon metal binding and facilitate return of the empty transporter to an outward-open state upon metal release.

Evaluation of clinical efficacy of Derinat® in form of spray in practice of district therapist

2019 ◽  
Vol 1 (9) ◽  
pp. 38-46
Author(s):  
A. P. Babkin ◽  
A. A. Zuikova ◽  
O. N. Krasnorutskaya ◽  
Yu. A. Kotova ◽  
D. Yu. Bugrimov ◽  
...  
Keyword(s):  
Clinical Efficacy ◽  
Respiratory Diseases ◽  
Viral Infections ◽  
Pharmacological Action ◽  
The Body ◽  
Natural Resistance ◽  
Acute Respiratory Diseases ◽  
T Helpers ◽  
T Killers ◽  
Stimulation Of

The widespread worldwide spread of acute respiratory diseases is an urgent problem in health care. Expressed polyetiology of respiratory diseases does not allow to limit the use of specific vaccine preparations and dictates the need to use to combat them a variety of non-specific means that stimulate the natural resistance of the human body. The main pharmacological action of sodium deoxyribonucleate is the stimulation of phagocytic activity of T-helpers and T-killers, increasing the functional activity of neutrophils and monocytes/ macrophages, providing regeneration and repair processes in the epithelial component of antiviral protection of the body. Based on the above, the study of the clinical efficacy of Derinat® in the form of spray in the treatment of acute respiratory viral infections is relevant.

Stimulation of distal potassium secretion by low lumen chloride in the presence of barium

1985 ◽  
Vol 248 (5) ◽  
pp. F638-F649 ◽  
Author(s):  
D. H. Ellison ◽  
H. Velazquez ◽  
F. S. Wright
Keyword(s):  
Chloride Concentration ◽  
Distal Tubule ◽  
Perfusion Fluid ◽  
Transport Pathway ◽  
Luminal Membrane ◽  
Potassium Secretion ◽  
Transepithelial Voltage ◽  
Tubule Fluid ◽  
Stimulation Of

Potassium secretion into the renal distal tubule is increased when chloride in the tubule fluid is replaced by another anion. The present experiments were done to determine whether this increment in transported potassium traverses a conductive pathway from cell to lumen. Transport rates of potassium, sodium, chloride, and fluid by the renal distal tubule of rats were examined in vivo by continuous microperfusion. The effects of substituting gluconate for chloride in the presence and absence of 5 mM barium in the perfusion fluid were determined. When gluconate replaced chloride in the perfusion solutions, potassium secretion increased (by 44%) without a significant change in transepithelial voltage. Barium in the lumen increased the magnitude of the lumen-negative transepithelial voltage (by 30%) and reduced potassium secretion (by 56%) by inhibiting conductive potassium movement. Barium also decreased both sodium (by 51%) and chloride (by 37%) absorption. Barium did not reduce the stimulation of potassium secretion caused by reducing lumen chloride concentration. Potassium secretion increased (by 77%) when lumen chloride was reduced in the presence of 5 mM barium. We interpret these results by postulating that a cotransport mechanism linking potassium and chloride is present in the luminal membrane of distal tubule cells, that this mechanism operates in parallel with a conductive transport pathway for potassium, and that the K-Cl cotransport mechanism is not inhibited by barium.

scholarly journals Proton Transport Pathway in the ClC Cl−/H+ Antiporter

2009 ◽  
Vol 97 (1) ◽  
pp. 121-131 ◽  
Author(s):  
Dong Wang ◽  
Gregory A. Voth
Keyword(s):  
Proton Transport ◽  
Transport Pathway

The stimulation of sodium transport by aldosterone

1971 ◽  
Vol 262 (842) ◽  
pp. 323-332 ◽  
Keyword(s):  
Protein Synthesis ◽  
Active Transport ◽  
Sodium Transport ◽  
Apical Plasma Membrane ◽  
Transport Pathway ◽  
Receptor Sites ◽  
Rna And Protein Synthesis ◽  
Inhibitor Of Protein Synthesis ◽  
Stimulation Of

Aldosterone, the major sodium retaining hormone in man, will stimulate active transport of sodium across the urinary bladder of the toad, Bufo marinus in vitro , at physiological concentrations of the hormone.The in vitro action of aldosterone is mimicked by steroid hormones with known mineralocorticoid properties and it is competitively inhibited by other analogues, e.g. spironolactone and cortisone. Aldosterone is bound to physiological receptor sites within the transporting epithelial cells, chiefly within the nuclei, and is displaced from these binding sites specifically by structural analogues including other mineralocorticoids. Effects of aldosterone are dependent upon availability of metabolizable substrates to support the active transport of sodium. Although the stimulation of sodium transport by aldosterone can be specifically inhibited by actinomycin D, an inhibitor of RNA synthesis, and by puromycin, an inhibitor of protein synthesis, direct evidence of stimulation of new RNA and protein synthesis during the latent period with physiological concentrations of aldosterone is still lacking. It is possible, however, that the amounts of RNA and protein that are involved are too small to be detected by available techniques. Evidence is summarized which leads us to conclude that the increased sodium transport induced by aldosterone is the consequence of a reduced resistance of the apical plasma membrane of the transporting epithelia to the entry of sodium into the transport pathway.

scholarly journals Silicon Mechanisms to Ameliorate Heavy Metal Stress in Plants

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Abolghassem Emamverdian ◽  
Yulong Ding ◽  
Yinfeng Xie ◽  
Sirous Sangari
Keyword(s):  
Heavy Metals ◽  
Heavy Metal ◽  
Enzyme Activity ◽  
Metal Uptake ◽  
Ph Value ◽  
Anthropogenic Activities ◽  
Heavy Metal Stress ◽  
Heavy Metal Uptake ◽  
Stimulation Of

The increased contaminants caused by anthropogenic activities in the environment and the importance of finding pathways to reduce pollution caused the silicon application to be considered an important detoxification agent. Silicon, as a beneficial element, plays an important role in amelioration of abiotic stress, such as an extreme dose of heavy metal in plants. There are several mechanisms involved in silicon mediation in plants, including the reduction of heavy metal uptake by plants, changing pH value, formation of Si heavy metals, and stimulation of enzyme activity, which can work by chemical and physical pathways. The aim of this paper is to investigate the major silicon-related mechanisms that reduce the toxicity of heavy metals in plants and then to assess the role of silicon in increasing the antioxidant enzyme and nonenzyme activities to protect the plant cell.

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