Electrostatic Compensation Restores Trafficking of the Autosomal Recessive Retinitis Pigmentosa E150K Opsin Mutant to the Plasma Membrane

Rhodopsin is the rod photoreceptor G protein-coupled receptor responsible for capturing light. Mutations in the gene encoding this protein can lead to a blinding disease called retinitis pigmentosa, which is inherited frequently in an autosomal dominant manner. The E150K opsin mutant associated with rarely occurring autosomal recessive retinitis pigmentosa localizes to trans-Golgi network membranes rather than to plasma membranes of rod photoreceptor cells. We investigated the molecular mechanisms underlying opsin retention in the Golgi apparatus. Electrostatic calculations reveal that the E150K mutant features an overall accumulation of positive charges between helices H-IV and H-II. Human E150K and several other closely related opsin mutants were then expressed in HEK-293 cells. Spectral characteristics and functional biochemistry of each mutant were analyzed after reconstitution with the cis-retinoid chromophore. UV-visible spectra and rhodopsin/transducin activation assays revealed only minor differences between the purified wild type control and rhodopsin mutants. However, partial restoration of the surface electrostatic charge in the compensatory R69E/E150K double mutant rescues the plasma membrane localization of opsin. These findings emphasize the fundamental importance of electrostatic interactions for appropriate membrane trafficking of opsin and advance our understanding of the pathophysiology of autosomal recessive retinitis pigmentosa due to the E150K mutation.     

Polysialic acid can mediate membrane interactions by interacting with phospholipids

Polysialic acid (polySia) is expressed on the surface of neural cells, neuroinvasive bacterial cells and several tumor cells. PolySia chains attached to NCAM can influence both trans interactions between membranes of two cells and cis interactions. Here, we report on the involvement of phospholipids in regulation of membrane interactions by polySia. The pH at the surface of liposomes, specific molecular area of phosphatidylcholine molecules, phase transition of DPPC bilayers, cyclic voltammograms of BLMs, and electron micrographs of phosphatidylcholine vesicles were studied after addition of polysialic acid free in solution. The results indicate that polySia chains can associate with phosphatidylcholine bilayers, incorporate into the polar part of a phospholipid monolayer, modulate cis interactions between phosphatidylcholine molecules, and facilitate trans interactions between apposing phospholipid vesicles. These observations imply that polySia attached to NCAM or to lipids can behave similarly.     

Polychaete fauna associated with holdfasts of the large brown alga Himantothallus grandifolius in Admiralty Bay, King George Island, Antarctic

The polychaete community associated with holdfasts of the brown alga Himantothallus grandifolius in Admiralty Bay has been studied. It is the first study of its kind in this area and only the second in the Antarctic. Samples were collected in the summer season of 1979/1980 from a depth range of 10–75 m. Seventy-eight species were found on 19 holdfasts. The community was dominated by Brania rhopalophora and Neanthes kerguelensis. Analysis of similarity showed that polychaete fauna associated with this habitat did not show any partitioning related to depth. Regression analysis showed that densities of both species and individuals decreased with increased holdfast volume. A positive correlation was found between the number of individuals and holdfast volume. Polychaetes from 10 feeding guilds were found with dominance of macrophagous motile herbivores and sessile filter feeders. The complex habitat provided by holdfasts is a shelter for a rich polychaete fauna and may function as important protection from disturbance in the shallow areas of Admiralty Bay.     

Molecular characteristics of community-associated methicillin-resistant Staphylococcus aureus strains for clinical medicine

Infections caused by methicillin-resistant S. aureus strains are mainly associated with a hospital setting. However, nowadays, the MRSA infections of non-hospitalized patients are observed more frequently. In order to distinguish them from hospital-associated methicillin-resistant S. aureus (HA-MRSA) strains, given them the name of community-associated methicillin-resistant S. aureus (CA-MRSA). CA-MRSA strains most commonly cause skin infections, but may lead to more severe diseases, and consequently the patient’s death. The molecular markers of CA-MRSA strains are the presence of accessory gene regulator (agr) of group I or III, staphylococcal cassette chromosome mec (SCCmec) type IV, V or VII and genes encoding for Panton–Valentine leukocidin (PVL). In addition, CA-MRSA strains show resistance to β-lactam antibiotics. Studies on the genetic elements of CA-MRSA strains have a key role in the unambiguous identification of strains, monitoring of infections, improving the treatment, work on new antimicrobial agents and understanding the evolution of these pathogens.     

Neuroprotective action of FK-506 (tacrolimus) after seizures induced with pilocarpine: quantitative and topographic elemental analysis of brain tissue

In the present work, X-ray fluorescence microscopy with a synchrotron source for the exciting radiation was applied for topographic and quantitative elemental analysis of rat brain tissue in pilocarpine-induced epilepsy and neuroprotection with FK-506. The mass per unit area of the elements P, S, Cl, K, Ca, Fe, Cu, Zn, Se, Br, and Rb was determined in four fields of the hippocampal formation (sectors 1 and 3 of Ammon’s horn–CA1, CA3; dentate gyrus; hilus of dentate gyrus) and the parietal cortex. The results obtained for epileptic rats treated with FK-506 (SNF) were compared with data obtained previously for epileptic rats (SNS) and a control group. Many statistically significant differences in elemental composition were observed between the SNF and SNS groups. Higher mass per unit area of P was noticed in CA1 and CA3 regions of the hippocampus of SNF rats in comparison with SNS rats. A similar relation was observed for K in all five brain areas analyzed. Also, Fe in CA3 and dentate gyrus, Cu in the parietal cortex, and Zn in CA3 and in the cortex were present at a higher level in the SNF group in comparison with the SNS group. The findings obtained in the present study suggest that the neuroprotective action of FK-506 in epileptic rat brain may involve not only the inhibition of calcineurin but also blockade of the K⁺ channels.     

Comparative molecular field analysis of fenoterol derivatives: A platform towards highly selective and effective β2-adrenergic receptor agonists

Purpose: To use a previously developed CoMFA model to design a series of new structures of high selectivity and efficacy towards the β₂-adrenergic receptor. Results: Out of 21 computationally designed structures 6 compounds were synthesized and characterized for β₂-AR binding affinities, subtype selectivities and functional activities. Conclusion: the best compound is (R,R)-4-methoxy-1-naphthylfelnoterol with K_iβ₂-AR = 0.28 μm, K_iβ₁-AR/K_iβ₂-AR = 573, EC_50cAMP = 3.9 nm, EC_50cardio = 16 nm. The CoMFA model appears to be an effective predictor of the cardiomocyte contractility of the studied compounds which are targeted for use in congestive heart failure.     

Different strategies of Cd tolerance and accumulation in Arabidopsis halleri and Arabidopsis arenosa

Pseudometallophytes are commonly used to study the evolution of metal tolerance and accumulation traits in plants. Within the Arabidopsis genus, the adaptation of Arabidopsis halleri to metalliferous soils has been widely studied, which is not the case for the closely related species Arabidopsis arenosa. We performed an in-depth physiological comparison between the A. halleri and A. arenosa populations from the same polluted site, together with the geographically close non-metallicolous (NM) populations of both species. The ionomes, growth, photosynthetic parameters and pigment content were characterized in the plants that were growing on their native site and in a hydroponic culture under Cd treatments. In situ, the metallicolous (M) populations of both species hyperaccumulated Cd and Zn. The NM population of A. halleri hyperaccumulated Cd and Zn while the NM A. arenosa did not. In the hydroponic experiments, the NM populations of both species accumulated more Cd in their shoots than the M populations. Our research suggests that the two Arabidopsis species evolved different strategies of adaptation to extreme metallic environments that involve fine regulation of metal homeostasis, adjustment of the photosynthetic apparatus and accumulation of flavonols and anthocyanins.     

Pannexin-1 channel “fuels” by releasing ATP from bone marrow cells a state of sterile inflammation required for optimal mobilization and homing of hematopoietic stem cells

An efficient harvest of hematopoietic stem/progenitor cells (HSPCs) after pharmacological mobilization from the bone marrow (BM) into peripheral blood (PB) and subsequent proper homing and engraftment of these cells are crucial for clinical outcomes from hematopoietic transplants. Since extracellular adenosine triphosphate (eATP) plays an important role in both processes as an activator of sterile inflammation in the bone marrow microenvironment, we focused on the role of Pannexin-1 channel in the secretion of ATP to trigger both egress of HSPCs out of BM into PB as well as in reverse process that is their homing to BM niches after transplantation into myeloablated recipient. We employed a specific blocking peptide against Pannexin-1 channel and noticed decreased mobilization efficiency of HSPCs as well as other types of BM-residing stem cells including mesenchymal stroma cells (MSCs), endothelial progenitors (EPCs), and very small embryonic-like stem cells (VSELs). To explain better a role of Pannexin-1, we report that eATP activated Nlrp3 inflammasome in Gr-1⁺ and CD11b⁺ cells enriched for granulocytes and monocytes. This led to release of danger-associated molecular pattern molecules (DAMPs) and mitochondrial DNA (miDNA) that activate complement cascade (ComC) required for optimal egress of HSPCs from BM. On the other hand, Pannexin-1 channel blockage in transplant recipient mice leads to a defect in homing and engraftment of HSPCs. Based on this, Pannexin-1 channel as a source of eATP plays an important role in HSPCs trafficking.