K:Cl cotransport: emerging molecular aspects of a ouabain-resistant, volume-responsive transport system in red blood cells

Erythrocytes from teleosts to mammals, like man, possess a ouabain-resistant K flux component which is Cl-dependent and activated upon suspension of the cells into hyposmotic media. This volume-responsive K:Cl cotransporter may be synonymous with a Cl-dependent K pathway stimulated by chemical interventions such as SH group (thiol) alkylation or oxidation at cytoplasmic sites of the membrane. Based on a comparison of the response of the two activity expressions of probably the same molecule to ionic and metabolic perturbations a molecular model is proposed accommodating K:Cl flux activities under a variety of stimulatory and inhibitory influences. Physiologically, this pathway may be involved in the maturational cell volume reduction occurring between the stages of reticulocytes and the final erythrocytes as well as corresponsible for the expression of the low K steady state of certain animal red blood cells. The pathophysiological potential of this K:Cl transporter lies in the fact that, when activated, red blood cells dehydrate through K:Cl loss.     

Microbiome Influences Prenatal and Adult Microglia in a Sex-Specific Manner

1. Download high-res image (242KB)
2. Download full-size image

     

Stimulation of active potassium transport in LK sheep red cells by blood group-L-antiserum

Summary Anti-L serum prepared by immunization of a high-potassium-type (HK) (blood type MM) sheep with blood from a low-potassium-type (LK) (blood type ML) sheep contained an antibody which stimulated four- to sixfold K⁺-pump influx in LK (LL) sheep red cells. In long-termin vitro incubation experiments, LK sheep red cells sensitized with anti-L showed a net increase in K⁺ after two days of incubation at 37°C, whereas HK-nonimmune (NI)-serum-treated control cells lost K⁺. The antibody could be absorbed by LK (LL) sheep red cells but not by HK sheep red cells. Kinetic experiments showed that the concentration of external K⁺ ([K⁺]₀) required to produce halfmaximum stimulation of the pump ([Na⁺]₀=0, replaced by Mg⁺⁺) was the same (0.25 mM) in L-antiserum-treated or untreated LK cells. LK cells with different [K⁺]_i (Na⁺ replacement) were prepared by the p-chloromercuribenzene sulfonate (PCMBS) method. At [K⁺]₀=5 mM, pump influx decreased as [K⁺]_i increased from 1 to 70 mM in L-antiserum-treated LK cells, whereas LK cells treated with HK-NI-serum ceased to pump at [K⁺]_i=35 mM. Exposure to anti-L serum produced an almost twofold increase in the number of pump sites of LK cells as measured by the binding of tritiated ouabain by LK sheep red cells. These findings indicate that the formation of a complex between the L-antigen and its antibody stimulates active transport in LK sheep red cells both by changing the kinetics of the pump and by increasing the number of pump sites.     

Role of Phosphorylation in Moesin Interactions with PIP2-Containing Biomimetic Membranes

Moesin, a protein of the ezrin, radixin, and moesin family, which links the plasma membrane to the cytoskeleton, is involved in multiple physiological and pathological processes, including viral budding and infection. Its interaction with the plasma membrane occurs via a key phosphoinositide, the phosphatidyl(4,5)inositol-bisphosphate (PIP₂), and phosphorylation of residue T558, which has been shown to contribute, in cellulo, to a conformationally open protein. We study the impact of a double phosphomimetic mutation of moesin (T235D, T558D), which mimics the phosphorylation state of the protein, on protein/PIP₂/microtubule interactions. Analytical ultracentrifugation in the micromolar range showed moesin in the monomer and dimer forms, with wild-type (WT) moesin containing a slightly larger fraction (～30%) of dimers than DD moesin (10–20%). Only DD moesin was responsive to PIP₂ in its micellar form. Quantitative cosedimentation assays using large unilamellar vesicles and quartz crystal microbalance on supported lipid bilayers containing PIP₂ reveal a specific cooperative interaction for DD moesin with an ability to bind two PIP₂ molecules simultaneously, whereas WT moesin was able to bind only one. In addition, DD moesin could subsequently interact with microtubules, whereas WT moesin was unable to do so. Altogether, our results point to an important role of these two phosphorylation sites in the opening of moesin: since DD moesin is intrinsically in a more open conformation than WT moesin, this intermolecular interaction is reinforced by its binding to PIP₂. We also highlight important differences between moesin and ezrin, which appear to be finely regulated and to exhibit distinct molecular behaviors.     

A non-tree-based comprehensive study of metazoan Hox and ParaHox genes prompts new insights into their origin and evolution

Background  

Hox and the closely-related ParaHox genes, which emerged prior to the divergence between cnidarians and bilaterians, are the most well-known members of the ancient genetic toolkit that controls embryonic development across all metazoans. Fundamental questions relative to their origin and evolutionary relationships remain however unresolved. We investigate here the evolution of metazoan Hox and ParaHox genes using the HoxPred program that allows the identification of Hox genes without the need of phylogenetic tree reconstructions.     

Amino-Acid Co-Variation in HIV-1 Gag Subtype C: HLA-Mediated Selection Pressure and Compensatory Dynamics

Background

Despite high potential for HIV-1 genetic variation, the emergence of some mutations is constrained by fitness costs, and may be associated with compensatory amino acid (AA) co-variation. To characterize the interplay between Cytotoxic T Lymphocyte (CTL)-mediated pressure and HIV-1 evolutionary pathways, we investigated AA co-variation in Gag sequences obtained from 449 South African individuals chronically infected with HIV-1 subtype C.

Methodology/Principal Findings

Individuals with CTL responses biased toward Gag presented lower viral loads than individuals with under-represented Gag-specific CTL responses. Using methods that account for founder effects and HLA linkage disequilibrium, we identified 35 AA sites under Human Leukocyte Antigen (HLA)-restricted CTL selection pressure and 534 AA-to-AA interactions. Analysis of two-dimensional distances between co-varying residues revealed local stabilization mechanisms since 40% of associations involved neighboring residues. Key features of our co-variation analysis included sites with a high number of co-varying partners, such as HLA-associated sites, which had on average 55% more connections than other co-varying sites.

Conclusions/Significance

Clusters of co-varying AA around HLA-associated sites (especially at typically conserved sites) suggested that cooperative interactions act to preserve the local structural stability and protein function when CTL escape mutations occur. These results expose HLA-imprinted HIV-1 polymorphisms and their interlinked mutational paths in Gag that are likely due to opposite selective pressures from host CTL-mediated responses and viral fitness constraints.     

Pathological effects of the microsporidium Nosema ceranae on honey bee queen physiology (Apis mellifera)

Nosema ceranae, a microsporidian parasite originally described in the Asian honey bee Apis cerana, has recently been found to be cross-infective and to also parasitize the European honey bee Apis mellifera. Since this discovery, many studies have attempted to characterize the impact of this parasite in A. mellifera honey bees. Nosema species can infect all colony members, workers, drones and queens, but the pathological effects of this microsporidium has been mainly investigated in workers, despite the prime importance of the queen, who monopolizes the reproduction and regulates the cohesion of the society via pheromones. We therefore analyzed the impact of N. ceranae on queen physiology. We found that infection by N. ceranae did not affect the fat body content (an indicator of energy stores) but did alter the vitellogenin titer (an indicator of fertility and longevity), the total antioxidant capacity and the queen mandibular pheromones, which surprisingly were all significantly increased in Nosema-infected queens. Thus, such physiological changes may impact queen health, leading to changes in pheromone production, that could explain Nosema-induced supersedure (queen replacement).