Mapping the ρ1 GABAC Receptor Agonist Binding Pocket

γ-Aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the mammalian brain. The GABA receptor type C (GABAC) is a ligand-gated ion channel with pharmacological properties distinct from the GABAA receptor. To date, only three binding domains in the recombinant ρ1 GABAC receptor have been recognized among six potential regions. In this report, using the substituted cysteine accessibility method, we scanned three potential regions previously unexplored in the ρ1 GABAC receptor, corresponding to the binding loops A, E, and F in the structural model for ligand-gated ion channels. The cysteine accessibility scanning and agonist/antagonist protection tests have resulted in the identification of residues in loops A and E, but not F, involved in forming the GABAC receptor agonist binding pocket. Three of these newly identified residues are in a novel region corresponding to the extended stretch of loop E. In addition, the cysteine accessibility pattern suggests that part of loop A and part of loop E have a β-strand structure, whereas loop F is a random coil. Finally, when all of the identified ligand binding residues are mapped onto a three-dimensional homology model of the amino-terminal domain of the ρ1 GABAC receptor, they are facing toward the putative binding pocket. Combined with previous findings, a complete model of the GABAC receptor binding pocket was proposed and discussed in comparison with the GABAA receptor binding pocket

Light-induced sulfur transport inside single-walled carbon nanotubes

This article belongs to the Section 2D and Carbon Nanomaterials.Filling of single-walled carbon nanotubes (SWCNTs) and extraction of the encapsulated species from their cavities are perspective treatments for tuning the functional properties of SWCNT-based materials. Here, we have investigated sulfur-modified SWCNTs synthesized by the ampoule method. The morphology and chemical states of carbon and sulfur were analyzed by transmission electron microscopy, Raman scattering, thermogravimetric analysis, X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopies. Successful encapsulation of sulfur inside SWCNTs cavities was demonstrated. The peculiarities of interactions of SWCNTs with encapsulated and external sulfur species were analyzed in details. In particular, the donor–acceptor interaction between encapsulated sulfur and host SWCNT is experimentally demonstrated. The sulfur-filled SWCNTs were continuously irradiated in situ with polychromatic photon beam of high intensity. Comparison of X-ray spectra of the samples before and after the treatment revealed sulfur transport from the interior to the surface of SWCNTs bundles, in particular extraction of sulfur from the SWCNT cavity. These results show that the moderate heating of filled nanotubes could be used to de-encapsulate the guest species tuning the local composition, and hence, the functional properties of SWCNT-based materials.This work was supported by the Russian Science Foundation (Project 18-72-00017), the bilateral Program “Russian-Germany Laboratory at BESSY II” in the part of XPS and C K-edge NEXAFS measurements, and shared research center SSTRC on the basis of the Novosibirsk VEPP-4 - VEPP-2000 complex at BINP SB RAS, using equipment supported by project RFMEFI62119X0022 in the part of S K-edge NEXAFS measurements. R.A. acknowledges the support from the Spanish Ministerio de Economia y Competitividad (MAT2016-79776-P, AEI/FEDER, EU), from the European Union’s Horizon 2020 programme under the project “ESTEEM3” (823717) and from the Government of Aragon and the European Social Fund under the project “Construyendo Europa desde Aragon” 2014–2020 (grant number E13_17R, FEDER, EU).Peer reviewe

Pro-oxidant Induced DNA Damage in Human Lymphoblastoid Cells: Homeostatic Mechanisms of Genotoxic Tolerance

Oxidative stress contributes to many disease etiologies including ageing, neurodegeneration, and cancer, partly through DNA damage induction (genotoxicity). Understanding the i nteractions of free radicals with DNA is fundamental to discern mutation risks. In genetic toxicology, regulatory authorities consider that most genotoxins exhibit a linear relationship between dose and mutagenic response. Yet, homeostatic mechanisms, including DNA repair, that allow cells to tolerate low levels of genotoxic exposure exist. Acceptance of thresholds for genotoxicity has widespread consequences in terms of understanding cancer risk and regulating human exposure to chemicals/drugs. Three pro-oxidant chemicals, hydrogen peroxide (H2O2), potassium bromate (KBrO3), and menadione, were examined for low dose-response curves in human lymphoblastoid cells. DNA repair and antioxidant capacity were assessed as possible threshold mechanisms. H2O2 and KBrO3, but not menadione, exhibited thresholded responses, containing a range of nongenotoxic low doses. Levels of the DNA glycosylase 8-oxoguanine glycosylase were unchanged in response to pro- oxidant stress. DNA repair–focused gene expression arrays reported changes in ATM and BRCA1, involved in double-strand break repair, in response to low-dose pro-oxidant exposure; however, these alterations were not substantiated at the protein level. Determination of oxidatively induced DNA damage in H2O2-treated AHH-1 cells reported accumulation of thymine glycol above the genotoxic threshold. Further, the H2O2 dose-response curve was shifted by modulating the antioxidant glutathione. Hence, observed pro- oxidant thresholds were due to protective capacities of base excision repair enzymes and antioxidants against DNA damage, highlighting the importance of homeostatic mechanisms in “genotoxic tolerance.

Inhibitor binding studies on enoyl reductase reveal conformational changes related to substrate recognition

Enoyl acyl carrier protein reductase (ENR) is involved in fatty acid biosynthesis. In Escherichia coli this enzyme is the target for the experimental family of antibacterial agents, the diazaborines, and for triclosan, a broad spectrum antimicrobial agent. Biochemical studies have suggested that the mechanism of diazaborine inhibition is dependent on NA

The Role of Microparticles of β-TCP and Wollastonite in the Creation of Biocoatings on Mg0.8Ca Alloy

The introduction of particles into the composition of coatings can significantly expand the range of properties and possibilities of the modified materials. In this work, the coatings containing microparticles of β-tricalcium phosphate (β-TCP) and wollastonite separately and in combination with each other were created on the surface of an Mg0.8Ca alloy. The morphology and microstructure of the coatings were examined by scanning and transmission electron microscopy. Their phase composition was determined with the help of X-ray diffraction analysis. The coating-to-substrate adhesion evaluation was carried out via the scratch-test method. Potentiodynamic polarization curves of the coatings were obtained during their immersion in 0.9% NaCl solution and their electrochemical properties were determined. Cytotoxic properties of the coatings were investigated by means of the MTT assay and flow cytometry in the course of the biological studies. In addition, NIH/3T3 cell morphology was analyzed using scanning electron microscopy. The structure, morphology, physical and mechanical, corrosive, and biological properties of the coatings depended on the type of particles they contained. Whereas the coating with β-TCP microparticles had higher adhesive properties, the coatings with wollastonite microparticles, as well as the combined coating, were less soluble and more biocompatible. In addition, the wollastonite-containing coating had the highest corrosion resistance

Role of interface interactions in the sensitivity of sulfur-modified single-walled carbon nanotubes for nitrogen dioxide gas sensing

Single-walled carbon nanotubes (SWCNTs) possess the unique ability to tune their functional properties by modifying the outer surface or interior space. Using the same modifier – sulfur, we demonstrate a difference in sensing properties of coated and filled single-walled carbon nanotubes to gaseous nitrogen dioxide. A comprehensive investigation of materials by transmission electron microscopy, X-ray photoelectron spectroscopy, density functional theory, and kinetics simulation led to an in-depth understanding of the factors influencing the sensor response of sulfur-modified SWCNTs, such as the role of surface and volumetric processes and interface effects. The sulfur-filled nanotubes with sulfur coating showed an outstanding sensitivity to detect nitrogen dioxide over a range from 1 ppb to 10 ppm due to the involvement of sulfur species in charge transfer between nanotubes and adsorbed molecules. Our data create a platform for the development of sensitive and reversible gas sensors using nanotube-based networks.The research was supported by the Ministry of Science and Higher Education of the Russian Federation (No. 121031700314-5). The authors thank the Helmholtz-Zentrum Berlin für Materialien und Energie for allocation of a beamtime and support within bilateral program “Russian-German Laboratory at BESSY II”. O.V. Sedelnikova acknowledges the Scholarship of the President of the Russian Federation (SP-1593.2021.1). The work on the fabrication of SWCNT films was supported by the Russian Science Foundation (grant 21-73-00229). V.O. Koroteev acknowledges financial support by the Spanish Ministry of Economy and Competitiveness (MINECO) within the Maria de Maeztu Units of Excellence Programme – MDM-2016-0618. A.A. Makarova acknowledges BMBF (grant no. 05K19KER). The EEL-SPIM inalysis was conducted at the Laboratorio de Microscopias Avanzadas (LMA) at the Instituto de Nanociencia de Aragon (INA) - Universidad de Zaragoza (Spain). R. Arenal acknowledges the support from the Spanish MICINN (PID2019-104739GB-100/AEI/10.13039/501100011033), from the European Union's Horizon 2020 programme under the project “ESTEEM3” (823717) and from the Government of Aragon (grant number E13_20R).Peer reviewe