Structural and mechanistic diversity of secondary transporters

Recent reports on the three-dimensional structure of secondary transporters have dramatically increased our knowledge of the translocation mechanism of ions and solutes. The structures of five transporters at atomic resolution have yielded four different folds and as many different translocation mechanisms. The structure of the glutamate transporter homologue Glt(Ph) confirmed the role of pore-loop structures as essential parts of the translocation mechanism in one family of secondary transporters. Biochemical evidence for pore-loop structures in several other families suggest that they might be common in secondary transporters, adding to the structural and mechanistic diversity of secondary transporters

Loop VIII/IX of the Na+-citrate transporter CitS of Klebsiella pneumoniae folds into an amphipathic surface helix

The sodium ion-dependent citrate transporter CitS of Klebsiella pneumoniae is a member of, the 2-hydroxycarboxylate transporter (2HCT) family whose members transport divalent citrate in symport with two sodium ions. Profiles of the hydrophobic moment suggested the presence of an amphipathic helical structure in the cytoplasmic loop between transmembrane segments (TMSs) VIII and IX (the AH loop) in all members of the family. Cysteine-scanning mutagenesis was used to study the secondary structure of the AH loop. We have mutated 20 successive residues into cysteine residues, characterized each of the mutants for its transport activity, and determined the accessibility of the residues. Three of the mutants, G324C, F331C, and F332C, had very low citrate transport activity, and two others, I321C and S333C, exhibited significantly decreased activity after treatment of right-side-out membranes with membrane permeable thiol reagent N-ethylmaleimide (NEM), but not with membrane impermeable 4-acetamido-4 '-maleimidylstilbene-2,2 '-disulfonic acid (AmdiS) and [2-(trimethylammonium)ethyl]methanethiosulfonate (MTSET). No protection against NEM was observed with citrate or sodium ions. Labeling of the cysteine residues in the 20 mutants with the fluorescent probe fluorescein 5-maleimide, in membrane vesicles with an inverted orientation, resulted in a clear periodicity in the accessibility of the residues. Residues expected to be at the hydrophobic face of the putative alpha-helix were not accessible for the label, whereas those at the hydrophilic face were easily accessed and labeled. Pretreatment of whole cells and inside-out membranes expressing the mutants with the membrane impermeable reagent AmdiS confirmed the cytoplasmic localization of the AH region. It is concluded that the loop between TMSs VIII and IX folds into an amphipathic surface helix

Accessibility of cysteine residues in a cytoplasmic loop of CitS of Klebsiella pneumoniae is controlled by the catalytic state of the transporter

The citrate transporter CAS of Klebsiella pneumoniae is a secondary transporter that transports citrate in symport with two sodium ions and one proton. Treatment of CAS with the alkylating, agent N-ethylmaleimide resulted in a complete loss of transport activity. Treatment of mutant proteins in which the five endogenous cysteine residues were mutated into serines in different combinations revealed that two cysteine residues located in the C-terminal cytoplasmic loop, Cys-398 and Cys-414, were responsible for the inactivation. Labeling with the membrane impermeable methanethiosulfonate derivatives MTSET and MTSES in right-side-out membrane vesicles showed that the cytoplasmic loop was accessible from the periplasmic side of the membrane. The membrane impermeable but more bulky maleimide AmdiS did not inactivate the transporter in right-side-out membrane vesicles. Inactivation by N-ethylmaleimide, MTSES, and MTSET was prevented by the presence of the co-ion Na+. Protection was obtained upon binding 2 Na+, which equals the transport stoichiometry. In the absence of Na+, the substrate citrate had no effect on the inactivation by permeable or impermeable thiol reagents. In contrast, when subsaturating concentrations of Na+ were present, citrate significantly reduced inactivation suggesting ordered binding of the substrate and co-ion; citrate is bound after Na+. In the presence of the proton motive force, the reactivity of the Cys residues was increased significantly for the membrane permeable N-ethylmaleimide, while no difference was observed for the membrane impermeable thiol reagents. The results are discussed in the context of a model for the opening and closing of the translocation pore during turnover of the transporter

Secondary transporters of the 2HCT family contain two homologous domains with inverted membrane topology and trans re-entrant loops

The 2-hydroxycarboxylate transporter (2HCT) family of secondary transporters belongs to a much larger structural class of secondary transporters termed ST3 which contains about 2000 transporters in 32 families. The transporters of the 2HCT family are among the best studied in the class. Here we detect weak sequence similarity between the N- and C-terminal halves of the proteins using a sensitive method which uses a database containing the N- and C-terminal halves of all the sequences in ST3 and involves BLAST searches of each sequence in the database against the whole database. Unrelated families of secondary transporters of the same length and composition were used as controls. The sequence similarity involved major parts of the N- and C-terminal halves and not just a small stretch. The membrane topology of the homologous N- and C-terminal domains was deduced from the experimentally determined topology of the members of the 2HCT family. The domains consist of five transmembrane segments each and have opposite orientations in the membrane. The N terminus of the N-terminal domain is extracellular, while the N terminus of the C-terminal domain is cytoplasmic. The loops between the fourth and fifth transmembrane segment in each domain are well conserved throughout the class and contain a high fraction of residues with small side chains, Gly, Ala and Ser. Experimental work on the citrate transporter CitS in the 2HCT family indicates that the loops are re-entrant or pore loops. The re-entrant loops in the N- and C-terminal domains enter the membrane from opposite sides (trans-re-entrant loops). The combination of inverted membrane topology and trans-re-entrant loops represents a new fold for secondary transporters and resembles the structure of aquaporins and models proposed for Na+/Ca2+ exchangers

Przedsiębiorstwa z kapitałem zagranicznym na tle przedsiębiorstw bez kapitału zagranicznego w województwie kujawsko-pomorskim

W artykule podjęto próbę zabrania głosu w dyskusji na temat oceny znaczenia kapitału zagranicznego dla gospodarki województwa kujawsko-pomorskiego poprzez przedstawienie przedsiębiorstw z kapitałem zagranicznym na tle przedsiębiorstw wyłącznie z polskim kapitałem. Celem opracowania jest porównanie przedsiębiorstw z kapitałem zagranicznym z przedsiębiorstwami bez kapitału zagranicznego z województwa kujawsko-pomorskiego pod względem: zasobów kapitałowych, zatrudnienia, nakładów inwestycyjnych oraz osiąganych wyników finansowych.This article is a trial of taking share in discussion about the importance of foreign capital for the economy of Kujawsko-Pomorskie voivodship through the presentation of companies with foreign capital against companies without foreign capital. The aim of this paper is to compare the companies with foreign capital and companies without foreign capital from Kujawsko-Pomorskie voivodship with regard to: capital resources, employment, investment outlays and financial results

Bezpośrednie inwestycje zagraniczne w województwie kujawsko-pomorskim

The inflow of foreign direct investment to kujawsko-pomorskie voivodship make chance to complete shortage of own investment possibilities in economy of region. In that paper is described the structure of foreign direct investment in kujawsko-pomorskie voivodship in 1999–2006 and the companies with foreign capital in this voivodship. There are presented also  problems  connected  with  foreign  direct  investment  and  labor  market  in  kujawsko-pomorskie voivodship.Napływ bezpośrednich inwestycji zagranicznych do województwa kujawsko-pomorskiego stwarza możliwość uzupełnienia niedoborów własnych możliwości inwestycyjnych w gospodarce regionu. W artykule opisano strukturę bezpośrednich inwestycji zagranicznych w województwie kujawsko-pomorskim w latach 1999–2006, a także przedsiębiorstwa z udzia-łem kapitału zagranicznego w tym województwie. Poruszone zostały również zagadnienia związane z bezpośrednimi inwestycjami zagranicznymi i rynkiem pracy w województwie kujawsko-pomorskim

Pharmacotherapy of heart failure A.D. 2023. Expert opinion of Working Group on Cardiovascular Pharmacotherapy, Polish Cardiac Society

Heart failure (HF) remains one of the most common causes of hospitalization and mortality among Polish patients. The position of the Section of Cardiovascular Pharmacotherapy presents the currently applicable options for pharmacological treatment of HF based on the latest European and American guidelines from 2021–2022 in relation to Polish healthcare conditions. Treatment of HF varies depending on its clinical presentation (acute/chronic) or left ventricular ejection fraction. Initial treatment of symptomatic patients with features of volume overload is based on diuretics, especially loop drugs. Treatment aimed at reducing mortality and hospitalization should include drugs blocking the renin-angiotensin-aldosterone system, preferably angiotensin receptor antagonist/neprilysin inhibitor, i.e. sacubitril/valsartan, selected beta-blockers (no class effect — options include bisoprolol, metoprolol succinate, or vasodilatory beta-blockers — carvedilol and nebivolol), mineralocorticoid receptor antagonist, and sodium-glucose cotransporter type 2 inhibitor (flozin), constituting the 4 pillars of pharmacotherapy. Their effectiveness has been confirmed in numerous prospective randomized trials. The current HF treatment strategy is based on the fastest possible implementation of all four mentioned classes of drugs due to their independent additive action. It is also important to individualize therapy according to comorbidities, blood pressure, resting heart rate, or the presence of arrhythmias. This article emphasizes the cardio- and nephroprotective role of flozins in HF therapy, regardless of ejection fraction value. We propose practical guidelines for the use of medicines, profile of adverse reactions, drug interactions, as well as pharmacoeconomic aspects. The principles of treatment with ivabradine, digoxin, vericiguat, iron supplementation, or antiplatelet and anticoagulant therapy are also discussed, along with recent novel drugs including omecamtiv mecarbil, tolvaptan, or coenzyme Q10 as well as progress in the prevention and treatment of hyperkalemia. Based on the latest recommendations, treatment regimens for different types of HF are discussed

Temperature Effects Explain Continental Scale Distribution of Cyanobacterial Toxins

Insight into how environmental change determines the production and distribution of cyanobacterial toxins is necessary for risk assessment. Management guidelines currently focus on hepatotoxins (microcystins). Increasing attention is given to other classes, such as neurotoxins (e.g., anatoxin-a) and cytotoxins (e.g., cylindrospermopsin) due to their potency. Most studies examine the relationship between individual toxin variants and environmental factors, such as nutrients, temperature and light. In summer 2015, we collected samples across Europe to investigate the effect of nutrient and temperature gradients on the variability of toxin production at a continental scale. Direct and indirect effects of temperature were the main drivers of the spatial distribution in the toxins produced by the cyanobacterial community, the toxin concentrations and toxin quota. Generalized linear models showed that a Toxin Diversity Index (TDI) increased with latitude, while it decreased with water stability. Increases in TDI were explained through a significant increase in toxin variants such as MC-YR, anatoxin and cylindrospermopsin, accompanied by a decreasing presence of MC-LR. While global warming continues, the direct and indirect effects of increased lake temperatures will drive changes in the distribution of cyanobacterial toxins in Europe, potentially promoting selection of a few highly toxic species or strains.Peer reviewe

Structural and functional features of the Na+-citrate transporter CitS of Klebsiella pneumoniae

One of the essential structures required by every living organism is a membrane that encompasses the cytoplasm (the contents of the cell). Membranes, not only have a very important role in sustaining contacts with the outside world, but also in protecting the cell against it. Whilst membranes have to be quite resistant to the stressful environment surrounding the cell, they also have to enable uptake of substrates and extrusion of waste products. .... Zie: Summary