[Show abstract][Hide abstract] ABSTRACT: A prominent degeneration of dopaminergic (DA-ergic) neurons in basal ganglia (striatum and substantia nigra) and a profound loss of dopamine resulting in patient motor dysfunctions are the main characteristics of Parkinson’s disease (PD). The data available indicate a substantial role of nicotinic acetylcholine receptors (nAChR) in molecular mechanisms underlying PD. nAChRs belong to the superfamily of ligand-gated ion channels, their pharmacological profile being determined by an array of subunits forming a distinct receptor subtype. Acetylcholine modulates dopamine release via an interaction with multiple nAChRs subtypes present on the nigrosriatal neurons. This suggests nAChRs as possible targets in the treatment of PD, however the knowledge of subunit composition is necessary for effective drug design. As studies in humans are quite limited, animal models are broadly used for these purposes. For creating experimental Parkinsonism models, low molecular weight toxic organic compounds are commonly used. 1-Methyl-4- phenyl-1,2,3,6-tetrahydropyridine (MPTP), 6-hydroxydopamine (6-OHDA), 1,1’-Dimethyl-4-4’-bypiridinium dichloride (paraquat), pesticide rotenone and ubiquitin proteasome system inhibitors, such as lactacystin and epoxomicin, can be mentioned as applied more often. Both mammalian and non-mammalian animals are used as model organisms, rodent and non-human primates being used mainly as mammalian models. This review summarizes the data obtained on toxic animal models about the involvement of different nAChR subtypes in PD at different stages. The present data suggest that degeneration of nigrostriatal DA-ergic neurons in the animal PD models is accompanied by alterations in the expression level and functional activity of different nAChR subtypes. Both heterooligomeric α6- and/or α4-containing and α7 homooligomeric subtypes are affected and can be regarded as possible targets for intervention.
[Show abstract][Hide abstract] ABSTRACT: For a small library of natural products from marine sponges and ascidians, in silico docking to the Lymnaea stagnalis acetylcholine-binding protein (AChBP), a model for the ligand-binding domains of nicotinic acetylcholine receptors (nAChRs), was carried out and the possibility of complex formation was revealed. It was further experimentally confirmed via competition with radioiodinated α-bungarotoxin ([125I]-αBgt) for binding to AChBP of the majority of analyzed compounds. Alkaloids pibocin, varacin and makaluvamines С and G had relatively high affinities (Ki 0.5-1.3 μM). With the muscle-type nAChR from Torpedo californica ray and human neuronal α7 nAChR, heterologously expressed in the GH4C1 cell line, no competition with [125I]-αBgt was detected in four compounds, while the rest showed an inhibition. Makaluvamines (Ki ~ 1.5 μM) were the most active compounds, but only makaluvamine G and crambescidine 359 revealed a weak selectivity towards muscle-type nAChR. Rhizochalin, aglycone of rhizochalin, pibocin, makaluvamine G, monanchocidin, crambescidine 359 and aaptamine showed inhibitory activities in electrophysiology experiments on the mouse muscle and human α7 nAChRs, expressed in Xenopus laevis oocytes. Thus, our results confirm the utility of the modeling studies on AChBPs in a search for natural compounds with cholinergic activity and demonstrate the presence of the latter in the analyzed marine biological sources.
[Show abstract][Hide abstract] ABSTRACT: The effects of nerve growth factor (NGF) from cobra venom (cvNGF) on growth of Ehrlich ascites carcinoma (EAC) cells inoculated subcutaneously in mice have been studied. The carcinoma growth slows down, but does not stop, during a course of cvNGF injections and restores after the course has been discontinued. The maximal anti-tumor effect has been observed at a dose of 8 nmoles cvNGF/kg body weight. cvNGF does not impact on lifespan of mice with grafted EAC cells. K252a, a tyrosine kinase inhibitor, attenuates the anti-tumor effect of cvNGF indicating the involvement of TrkA receptors in the process. cvNGF has induced also increase in body weight of the experimental animals. In overall, cvNGF shows the anti-tumor and weight-increasing effects which are opposite to those described for mammalian NGF (mNGF). However in experiments on breast cancer cell line MCF-7 cvNGF showed the same proliferative effects as mNGF and had no cytotoxic action on tumor cells in vitro. These data suggest that cvNGF slows down EAC growth via an indirect mechanism in which TrkA receptors are involved.
[Show abstract][Hide abstract] ABSTRACT: We describe cloning and expression of genes coding for lipase Lip2Pc and lipase-specific foldase LifPc from a psychrotrophic microorganism Psychrobacter cryohalolentis K5(T) isolated from a Siberian cryopeg (the lense of overcooled brine within permafrost). Upon expression in E. coli Lip2Pc accumulated in inclusion bodies while chaperone was synthesized in a soluble form. An efficient protocol for solubilization and subsequent refolding of the recombinant lipase in the presence of the truncated chaperone was developed. Using this procedure Lip2Pc with specific activity of 6900 U/mg was obtained. Contrary to published data on other lipase-chaperone complexes, refolded Lip2Pc was mostly recovered from the complex with chaperone by metal-affinity chromatography. Recombinant Lip2Pc displayed maximum lipolytic activity at 25°C and pH 8.0 with p-nitrophenyl palmitate (C16) as a substrate. Activity assays conducted at different temperatures revealed that the recombinant Lip2Pc is a cold-adapted lipase with ability to utilize substrates with long (C10-C16) hydrocarbon chains in the temperature range from +5 to +65°C. It demonstrated relatively high stability at temperatures above 60°C and in the presence of various metal ions or organic solvents (ethanol, methanol, etc.). Non-ionic detergents, such as Triton X-100 and Tween 20 decreased Lip2Pc activity and SDS completely inhibited it.
Protein Expression and Purification 07/2013; 91(1). DOI:10.1016/j.pep.2013.07.011 · 1.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Human LYNX1, belonging to the Ly6/neurotoxin family of three-finger proteins, is membrane-tethered with a GPI anchor and modulates the activity of nicotinic acetylcholine receptors (nAChR). Recent preparation of LYNX1 as an individual protein in the form of water-soluble domain lacking GPI anchor (ws-LYNX1; Lyukmanova et al, 2011) revealed the attachment at the agonist-binding site in the acetylcholine-binding protein (AChBP) and muscle nAChR but outside it in the neuronal nAChRs. Here we obtained a series of ws-LYNX1 mutants (T35A, P36A, T37A, R38A, K40A, Y54A, Y57A, K59A) and examined by radioligand analysis or patch-clamp technique their interaction with the AChBP, Torpedo californica nAChR and chimeric receptor composed of the α7 nAChR extracellular ligand-binding domain and the transmembrane domain of α1 glycine receptor (α7-GlyR). Against AChBP there was either no change in activity (T35A, T37A), slight decrease (K40A, K59A) and even enhancement for the rest mutants (most pronounced for P36A and R38A). With both receptors many mutants lost inhibitory activity, but the increased inhibition was observed for P36A at α7-GlyR. Thus, there are subtype-specific and common ws-LYNX1 residues recognizing distinct targets. Since ws-LYNX1 was inactive against glycine receptor, its ″non-classical″ binding sites on α7 nAChR should be within the extracellular domain. Micromolar affinities and fast washout rates measured for ws-LYNX1 and its mutants are in contrast to nanomolar affinities and irreversibility of binding for α-bungarotoxin and similar snake α-neurotoxins also targeting α7 nAChR. This distinction may underlie their different actions, i.e. nAChRs modulation versus irreversible inhibition, for these two types of three-finger proteins.
[Show abstract][Hide abstract] ABSTRACT: Azemiopsin, a novel polypeptide, was isolated from the Azemiops feae viper venom by combination of gel filtration and reverse-phase HPLC. Its amino acid sequence (DNWWPKPPHQGPRPPRPRPKP) was determined by means of Edman degradation and mass spectrometry. It consists of 21 residues and, unlike similar venom isolates, does not contain cysteine residues. According to circular dichroism measurements, this peptide adopts a β-structure. Peptide synthesis was used to verify the determined sequence and to prepare peptide in sufficient amounts to study its biological activity. Azemiopsin efficiently competed with α-bungarotoxin for binding to Torpedo nicotinic acetylcholine receptor (nAChR) (IC(50) 0.18 ± 0.03 μm) and with lower efficiency to human α7 nAChR (IC(50) 22 ± 2 μm). It dose-dependently blocked acetylcholine-induced currents in Xenopus oocytes heterologously expressing human muscle-type nAChR and was more potent against the adult form (α1β1εδ) than the fetal form (α1β1γδ), EC(50) being 0.44 ± 0.1 μm and 1.56 ± 0.37 μm, respectively. The peptide had no effect on GABA(A) (α1β3γ2 or α2β3γ2) receptors at a concentration up to 100 μm or on 5-HT(3) receptors at a concentration up to 10 μm. Ala scanning showed that amino acid residues at positions 3-6, 8-11, and 13-14 are essential for binding to Torpedo nAChR. In biological activity azemiopsin resembles waglerin, a disulfide-containing peptide from the Tropidechis wagleri venom, shares with it a homologous C-terminal hexapeptide, but is the first natural toxin that blocks nAChRs and does not possess disulfide bridges.
[Show abstract][Hide abstract] ABSTRACT: Nicotinic acetylcholine receptors (nAChRs) are involved in the regulation of intracellular Ca2+-dependent processes both in normal and pathological states. α-Conotoxins from the venom of Conus marine mollusks are a valuable tool for the investigation of the pharmacological action and functional role of nAChRs. Analogues of α-conotoxin MII labeled by Bolton-Hunter reagent (BH-MII) or fluorescein isothiocyanate (FITC-MII) on the N-terminal glycine residue have been synthesized in the present work. Fluorescence microscopy studies of SH-SY5Y neuroblastoma cells loaded with Ca2+ indicator Fura-2, or by both Ca2+ indicator Fluo-4 and Na+ indicator SBFI, were used to test the effect of MII modification on its ability to block Ca2+ and Na+ signals induced by nicotine. Measurements in SH-SY5Y cells showed that kinetics of the increase and recovery of the concentration of free Ca2+ ([Ca2+]i
) upon nicotine application and washout was different from that for free Na+ ([Na+]i
), this being evidence of differences in the mechanism of Ca2+ and Na+ homeostasis regulation. MII suppressed the nicotine-induced increase of [Ca2+]i
in a concentration-dependent manner. An additional tyrosine residue added to the N-terminus of one of the MII derivatives caused a significant decrease in the inhibitory action of MII; this decrease was even more pronounced when a large FITC label was introduced into MII. The BH-MII derivative had an inhibitory effect similar to that of unmodified α-conotoxin. MII and its iodinated derivatives are promising tools for radioligand assays.
[Show abstract][Hide abstract] ABSTRACT: Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that mediate synaptic transmission in the muscle and autonomic ganglia and regulate transmitter release in the brain. The nAChRs composed of α7 subunits are also expressed in non-excitable cells to regulate cell survival and proliferation. Up to now, functional α7 nAChRs were found exclusively on the cell plasma membrane. Here we show that they are expressed in mitochondria and regulate early pro-apoptotic events like cytochrome c release. The binding of α7-specific antibody with mouse liver mitochondria was revealed by electron microscopy. Outer membranes of mitochondria from the wild-type and β2-/- but not α7-/- mice bound α7 nAChR-specific antibody and toxins: FITC-labeled α-cobratoxin or Alexa 555-labeled α-bungarotoxin. α7 nAChR agonists (1 µM acetylcholine, 10 µM choline or 30 nM PNU-282987) impaired intramitochondrial Ca(2+) accumulation and significantly decreased cytochrome c release stimulated with either 90 µM CaCl(2) or 0.5 mM H(2)O(2). α7-specific antagonist methyllicaconitine (50 nM) did not affect Ca(2+) accumulation in mitochondria but attenuated the effects of agonists on cytochrome c release. Inhibitor of voltage-dependent anion channel (VDAC) 4,4'-diisothio-cyano-2,2'-stilbene disulfonic acid (0.5 µM) decreased cytochrome c release stimulated with apoptogens similarly to α7 nAChR agonists, and VDAC was co-captured with the α7 nAChR from mitochondria outer membrane preparation in both direct and reverse sandwich ELISA. It is concluded that α7 nAChRs are expressed in mitochondria outer membrane to regulate the VDAC-mediated Ca(2+) transport and mitochondrial permeability transition.
PLoS ONE 02/2012; 7(2):e31361. DOI:10.1371/journal.pone.0031361 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We studied the ability of four non-conjugated alpha7-subunit fragments of the nicotinic acetylcholine receptor to induce an immune response and to protect memory in olfactory bulbectomized mice which demonstrate abnormalities similar to Alzheimer's disease (AD). Vaccination only with the alpha7-subunit fragment 173-193 was shown to rescue spatial memory, to restore the level of alpha7 acetylcholine receptors in the cortex, and to prevent an increase in the amyloid-beta (Abeta) level in brain tissue in these animals. Antibodies against the peptide 173-193 were revealed in blood serum and cerebrospinal liquid in the bulbectomized mice. Passive immunization with mouse blood sera containing antibodies to the peptide 173-193 also restored memory in bulbectomized animals. The observed positive effect of both active and passive immunization with the fragment of alpha7-subunit on memory of bulbectomized mice provides a new insight into an anti-AD drug design.
[Show abstract][Hide abstract] ABSTRACT: In complex tissues where multiple subtypes of nicotinic acetylcholine receptors (nAChRs) are expressed, immunohistochemistry has been the most popular tool for investigation of nAChR subunit distribution. However, recent studies with nAChR subunit knockout mice demonstrated that a large panel of antibodies is unsuitable. Thus, we aimed to develop a histochemical method for selective labeling of alpha7 nAChR with neurotoxins, utilizing alpha7 nAChR-transfected cells, dorsal root ganglia (DRG) and spinal cord from wild-type and knockout mouse. The specificity of Alexa Fluor 488-conjugated alpha-bungarotoxin (Alexa-alphaBgt) was demonstrated in binding to alpha7-transfected cells inhibited by long-chain alpha-cobratoxin (CTX), but not short-chain alpha-neurotoxin II (NTII). In contrast, binding to Torpedo muscle-type nAChRs and to motor end plates in mouse tongue sections was prevented by both CTX and NTII. In tissue sections of DRG, expressing all neuronal nAChR subunits, only CTX precluded Alexa-alphaBgt labeling of neurons, with no staining for alpha7 nAChR knockout tissue. It proved that alpha7 nAChRs are the major alphaBgt-binding sites in mouse DRG. Corresponding results were obtained for terminals in the spinal cord. Thus, we present a protocol utilizing Alexa-alphaBgt and non-labeled CTX/NTII that allows specific histochemical detection of alpha7 nAChR with a spatial resolution at the level of single axon terminals.
Journal of Neurochemistry 06/2009; 109(4):1087-95. DOI:10.1111/j.1471-4159.2009.06033.x · 4.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Neuronal nicotinic acetylcholine receptors (nAChRs) containing alpha7 subunit are well represented in the brain and some non-neuronal tissues, and their malfunctioning is associated with diverse pathologies. Therefore, detection and quantification of alpha7 nAChR are important tasks. The affinity-purified antibodies were prepared against the 1-23 and 179-190 fragments of the human and rat alpha7 nAChR extracellular domain. The specificity and selectivity of these alpha7 (1-23) and alpha7 (179-190) antibodies was tested by ELISA in model systems: the E. coli-expressed alpha7 subunit extracellular domain and the pituitary cell line GH(4)C(1) stably expressing human alpha7 nAChR. On the rat brain slices two antibodies and biotinylated alpha-cobratoxin specifically stained the hippocampus region known to be rich in alpha7 nAChR. Western blot analysis revealed that in the human thalamus membranes and in rat brain membranes, antibodies alpha7 (1-23) stained a single band of 62 kDa, while the alpha7 (179-190) antibodies stained a doublet of 53-54 kDa. The results obtained show that utilization of model systems and a combination of several antibodies with appropriately labeled toxins may provide better ways for detection of alpha7 nAChR.
Life Sciences 06/2007; 80(24-25):2202-5. DOI:10.1016/j.lfs.2007.01.007 · 2.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We have compared specificity of a panel of polyclonal antibodies against synthetic fragments of the alpha7 subunit of homooligomeric acetylcholine receptor (AChR) and some subunits of heteromeric AChRs. The antibody interaction with extracellular domain of alpha7 subunit of rat AChR (residues 7-208) produced by heterologous expression in E. coli and rat adrenal membranes was investigated by the ELISA method. For comparison, membranes from the Torpedo californica ray electric organ enriched in muscle-type AChR and polyclonal antibodies raised against the extracellular domain (residues 1-209) of the T. californica AChR alpha1 subunit were also used. Antibody specificity was also characterized by Western blot analysis using rat AChR extracellular domain alpha7 (7-208) and the membrane-bound T. californica AChR. Epitope localization was analyzed within the framework of AChR extracellular domain model based on the crystal structure of acetylcholine-binding protein available in the literature. According to this analysis, the 179-190 epitope is located on loop C, which is exposed and mobile. Use of antibodies against alpha7 (179-190) revealed the presence of alpha7 AChR in rat adrenal membranes.
[Show abstract][Hide abstract] ABSTRACT: Polyclonal antibodies obtained by immunization of rabbits with native form of weak toxin (WTX) from cobra Naja kaouthia venom efficiently interacted with WTX and a weak toxin from Naja oxiana venom, but not so with their denaturated forms. These antibodies could also bind with lower affinity other groups of three-fingered toxins: long-chain alpha-neurotoxins, muscarinic toxins and cytotoxins, but practically did not bind short-chain alpha-neurotoxins. The efficiency of toxin-antibody interaction depends on the group (weak toxins, long or short alpha-neurotoxins, cytotoxins etc.) to which the toxin belongs, but not on species of snake from which the toxin originates. There is a correlation between the results obtained and phylogenetic analysis of the three-fingered toxins which revealed that WTX is very close to other weak toxins, relatively close to long alpha-neurotoxins, cytotoxins and muscarinic toxins, but is distant from the short alpha-neurotoxins.
[Show abstract][Hide abstract] ABSTRACT: A basic glycoprotein oxiagin with molecular mass of 49.8 kDa was isolated from the venom of Central Asian cobra Naja oxiana. Partial amino acid sequence determination has shown that oxiagin belongs to reprolysins, a subfamily of animal metalloproteinases possessing a characteristic multidomain structure. Oxiagin was found to inhibit the classical pathway of the complement system. A study of the oxiagin influence on the different stages of the classical pathway showed that it inhibited the formation of C3-convertase. To achieve it, oxiagin binds to IgG on the surface of sheep erythrocytes sensitized with rabbit antibodies, thus, preventing the interaction of component C2 (without its inactivation) with immobilized C4b. IC50 for the inhibiton of classical pathway of complement system by oxiagin is 80 nM, while it does not affect the alternative pathway at concentrations up to 1.2 microM. Oxiagin possessed hemagglutinating activity towards sheep and rabbit erythrocytes, and this activity as well as the complement inhibition by oxiagin were suppressed by D-galactose. Oxiagin is the first representative of snake venom reprolysins that inhibits the complement system, utilizing non-proteolytic inhibiting strategy.
[Show abstract][Hide abstract] ABSTRACT: A protein corresponding to the extracellular 1-209 domain of the alpha-subunit of the nicotine acetylcholine receptor from the electric organ of Torpedo californica was prepared using the corresponding cDNA domain by culturing Escherichia coli cells on a synthetic medium supplemented with 5-fluoro-L-tryptophan. The presence of a (His)(6) fragment preceding the 1-209 sequence allowed purification of the protein isolated from inclusion bodies by affinity chromatography on Ni-NTA A-arose. The incorporation of 5-fluorotryptophan residues was found by (FNMR)-F-19 to be similar to50%. The spectrum of the protein reduced in the denaturing conditions and subsequently reoxidized in a dilute solution under denaturing conditions in the presence of 0.05% SDS was sufficiently resolved, which allowed partial assignment of (19)resonances using the Trp60Phe mutant protein. The ability of the prepared domains to specifically bind snake alpha-neurotoxins was demonstrated with the use of radioiodinated alpha-bungarotoxin and trifluoroacetylated a-cobratoxin.
[Show abstract][Hide abstract] ABSTRACT: A sensitive nonradioactive method for detection of substances interacting with the neuronal 7-type nicotinic acetylcholine receptor (AChR) was proposed. The method uses biotinylated -cobratoxin (Bt-CTX) and is based on the ability of the N-terminal ligand-binding extracellular domain (LBED) of AChR to interact with -cobratoxin (CTX) as does the whole receptor. LBED produced by heterologous expression of a gene fragment of the 7 subunit of AChR from the rat brain in Escherichia coli cells was sorbed in wells of a 96-well plate and incubated with Bt-CTX. The specifically bound Bt-CTX was determined by staining with streptavidin–peroxidase complex. The ability of other compounds to interact with 7-AChR was checked according to the degree with which they inhibit the Bt-CTX binding to LBED. Nicotine, carbamylcholine, d-tubocurarin, anabaseine, conotoxin ImI, and neurotoxin II were used as model compounds. The sensitivity of this method was comparable with that of the radioligand method (up to 10 pmol).