Beta Epsilon Research Articles

A beta–epsilon distribution: properties and applications

A beta–epsilon distribution: properties and applications

Death of a neonatal lamb due to Clostridium perfringens type B in New Zealand

ABSTRACTCase history and clinical findings: A flock of 20 sheep was kept within three paddocks on a single property. None of the animals in the flock had been vaccinated against any disease for at least three years. Abdominal bloating and haemorrhagic diarrhoea were observed in Lamb 1 at 24 hours-of-age. The lamb subsequently died within an hour of the onset of clinical signs. Lamb 2 was 3-days-old when observed to be recumbent with opisthotonus. The lamb was treated with dextrose, vitamins B1 and B12, and penicillin G, but died 4 hours later.Pathological findings: Examination of Lamb 1 revealed markedly increased gas within the peritoneum and within dilated loops of intestine. The intestines were dark red and contained large quantities of haemorrhagic fluid. Histology of the intestines revealed peracute mucosal necrosis with minimal accompanying inflammation. The intestinal lumen contained cell debris, haemorrhage, and myriad large Gram-positive bacilli. The intestines of Lamb 2 did not appear bloated or reddened. However, multiple fibrin clots were visible within the pericardial sac. Histopathological examination revealed small foci of necrosis within the mucosa of the distal intestine. The necrotic foci were often associated with large numbers of large Gram-positive bacilli.Immunohistochemsitry and molecular biology: Intestinal samples from Lamb 1 were processed for Clostridium perfringens immunohistochemistry, which revealed large numbers of intralesional, positively immunostained rods. Fragments corresponding to the expected sizes for genes encoding alpha, beta, and epsilon C. perfringens typing toxins were amplified by PCR from DNA extracted from formalin-fixed sections of intestine.Diagnosis: Lamb dysentery due to C. perfringens type B.Clinical relevance: C. perfringens bacteria have a worldwide distribution, but disease due to C. perfringens type B has only been diagnosed in a small number of countries and has never been reported in New Zealand or Australia. C. perfringens type B produce both beta toxin and epsilon toxins, therefore both haemorrhagic enteritis and systemic vascular damage can develop. As many animals are exposed to C. perfringens without developing disease, there must be additional unknown factors that resulted in disease in these particular sheep. Vaccines that specifically protect against C. perfringens type B are available and may be recommended for use in smaller non-commercial flocks, as in the present case.

Molecular Descriptors of N‐Arylhydroxamic Acids: A Tool in Drug Design

The partition coefficient in the 1-octanol/water system, log P(O/W), is a measure of lipophilicity. It is used as a predictor of solute-membrane partitioning. The objective of this study was to measure the log P(O/W) of five hydroxamic acids. Other molecular descriptors of these solutes, namely molar volume, molar refraction, parachor, polarizability (pi*), hydrogen-bond donor acidity (epsilon alpha) and hydrogen-bond acceptor basicity (epsilon beta), have also been discussed. These properties represent the combined effects of a number of intermolecular forces between a solute and its environment.

Fulbright Scholar Opportunities for Scholars and Students

Journal of Nursing ScholarshipVolume 36, Issue 3 p. 191-191 Fulbright Scholar Opportunities for Scholars and Students Patrice K . Nicholas RN, DNSc, MPH, ANP, Epsilon Beta & Theta-at-Large, Patrice K . Nicholas RN, DNSc, MPH, ANP, Epsilon Beta & Theta-at-LargeSearch for more papers by this author Thomas P . Nicholas, Thomas P . NicholasSearch for more papers by this author Patrice K . Nicholas RN, DNSc, MPH, ANP, Epsilon Beta & Theta-at-Large, Patrice K . Nicholas RN, DNSc, MPH, ANP, Epsilon Beta & Theta-at-LargeSearch for more papers by this author Thomas P . Nicholas, Thomas P . NicholasSearch for more papers by this author First published: 02 September 2004 https://doi.org/10.1111/j.1547-5069.2004.04036.xCitations: 1Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume36, Issue3September 2004Pages 191-191 RelatedInformation

Divergence function, duality, and convex analysis.

From a smooth, strictly convex function phi: Rn --> R, a parametric family of divergence function Dphi(alpha) may be introduced: [ equation: see text] for x, y epsilon int dom (Phi) subset Rn, and for alpha in R, with Dphi(+/-1) defined through taking the limit of alpha. Each member is shown to induce an alpha-independent Riemannian metric, as well as a pair of dual alpha-connections, which are generally nonflat, except for alpha = +/-1. In the latter case, Dphi(+/-1) reduces to the (nonparametric) Bregman divergence, which is representable using phi and its convex conjugate phi* and becomes the canonical divergence for dually flat spaces (Amari, 1982, 1985; Amari & Nagaoka, 2000). This formulation based on convex analysis naturally extends the informationgeometric interpretation of divergence functions (Eguchi, 1983) to allow the distinction between two different kinds of duality: referential duality (alpha <--> -alpha) and representational duality (phi <--> phi*). When applied to (not necessarily normalized) probability densities, the concept of conjugated representations of densities is introduced, so that +/-alpha-connections defined on probability densities embody both referential and representational duality and are hence themselves bidual. When restricted to a finite-dimensional affine submanifold, the natural parameters of a certain representation of densities and the expectation parameters under its conjugate representation form biorthogonal coordinates. The alpha representation (indexed by beta now, beta epsilon [-1, 1]) is shown to be the only measure-invariant representation. The resulting two-parameter family of divergence functionals D(alpha,beta), (alpha, beta) epsilon [-1, 1] x [-1, 1] induces identical Fisher information but bidual alpha-connection pairs; it reduces in form to Amari's alpha-divergence family when alpha = +/-1 or when beta = 1, but to the family of Jensen difference (Rao, 1987) when beta = -1.

Effect of protein kinase C on transmembrane calcium fluxes in HaCaT keratinocytes

Capacitive calcium influx is associated with the release of calcium from internal stores and participates in intracellular calcium homeostasis. In keratinocytes, its activation is linked to the stimulation of the phospho-inositide (PI) pathway and seems to be altered in psoriasis. An overnight treatment of isolated HaCaT keratinocytes with phorbol 12-myristate 13-acetate (PMA) selectively downregulated the classical, calcium-dependent protein kinase C (PKC) isoenzyme PKC alpha in preconfluent cells. This was parallelled by an increased capacitative calcium influx with no effects on the PI pathway. These observations were strengthened in measurements using cyclopiazonic acid which revealed a 47% increase in PMA pretreated as compared with control cells in the calcium influx rate through store-operated calcium channels (SOC-s) following the emptying of the intracellular calcium stores. In confluent as compared with preconfluent cultures PKC epsilon was markedly increased, while other isoenzymes were not affected. In parallel, the kinetics of capacitative calcium influx were altered, showing clear inactivation. PMA pretreatment in these cells had little effect on PKC alpha but downregulated both PKC beta and PKC epsilon, and did not increase the influx through SOC-s. These observations support the differential regulation of SOC-s by PKC and suggest the involvement of several PKC isoenzymes in human keratinocytes.

Changes in mRNA expression of nicotinic acetylcholine receptor subunits during embryonic development of mouse masseter muscle.

Nicotinic acetylcholine receptors (nAChRs) switch from the embryonic-type (alpha 2 beta gamma delta subunits) to the adult-type (alpha 2 beta epsilon delta subunits), and disappear besides the neuromuscular junctions with the development of trunk and limb skeletal muscles. However, little is known about this process during the embryonic development of masseter muscle. To identify the time course of the nAChR transition from embryonic day (E) 11 to the newborn stage in mouse masseter muscle, we analyzed the expression level of delta, epsilon, and gamma subunit mRNAs by competitive polymerase chain reaction in combination with reverse transcription as well as distribution of delta subunit protein by immunohistochemistry. The nAChR delta subunit mRNA was initially detected at E11, showed an approximately 25-fold increase (p < 0.0001) between E11 and E17, and plateaued thereafter until the newborn stage. Immunostaining for delta subunit was observed in the whole portions of masseter myofibers at E17 and birth, suggesting that the nAChR elimination does not begin even at the newborn stage. The epsilon subunit mRNA initially appeared at E17, and increased in quantity by 144% (p < 0.0001) up to the newborn stage. The quantity of gamma subunit mRNA increased by approximately 240% (p < 0.0001) between E11 and E17, and then decreased by 22% (p < 0.05) from E17 value at the newborn stage. The beginning of the expression of the epsilon subunit mRNA was coincident with the beginning of the decrease in the quantity of the gamma subunit mRNA, suggesting that the nAChR subunit switch begins at E17.

Compressibility sum rule for the two-dimensional electron gas

The authors establish formulas for the isothermal compressibility and long-wavelength static density-density response function of a weakly correlated two-dimensional electron gas in the 1<<beta epsilon(F)<infinity and 0< or =beta epsilon(F)<<1 degeneracy domains; beta epsilon(F)=pi n Planck's over 2 pi(2)/(mk(B)T). The calculation of the pressure in the former domain is based on the Isihara-Toyoda formula [A. Isihara and T. Toyoda, Phys. Rev. B 21, 3358 (1980)] for the exchange-correlation energy at finite temperature. The pressure calculation in the latter domain is based on the Totsuji classical cluster-expansion formula for the correlation energy [H. Totsuji, J. Phys. Soc. Jpn. 40, 857 (1976); Phys. Rev. A 19, 889 (1979)].

Human neuronal threonine-for-leucine-248 alpha 7 mutant nicotinic acetylcholine receptors are highly Ca2+ permeable

A cDNA coding for the human neuronal nicotinic alpha7 receptor subunit with Leu-248 mutated to threonine was expressed in Xenopus oocytes. When activated by acetylcholine (AcCho), the receptors expressed generated currents that had low desensitization, linear current-voltage relation, and high apparent affinity for both AcCho and nicotine. These characteristics are similar to those already described for the chick threonine-for-leucine-247 alpha7 nicotinic AcCho receptor (nAcChoR) mutant (L247Talpha7). These properties were all substantially maintained when the human L248Talpha7 mutant was transiently expressed in human Bosc 23 cells. Simultaneous whole-cell clamp and fluorescence measurements with the Ca(2+) indicator dye Fura-2 showed that nicotine induced a Ca(2+) influx in standard 2 mM Ca(2+) solution. The average fractional Ca(2+) current flowing through L248Talpha7 nAcChoRs was 6.7%, which is larger than that flowing through muscle alpha(beta)epsilon(delta) nAcChoRs (4.1%). The relative Ca(2+) permeability, determined in oocytes in the absence of Cl(-), was measured from the shift in reversal potential caused by increasing the external Ca(2+) concentration from 1 to 10 mM. The human wild-type alpha7 nAcChoR was found to be more permeable than the L248Talpha7 mutant to Ca(2+). Our findings indicate that the Ca(2+) permeability of the homomeric alpha7 nAcChoR is larger than that of the heteromeric neuronal nicotinic receptors studied to date and is possibly similar to that of the N-methyl-D-aspartate subtype of brain glutamate receptors.

Molecular mechanisms mediating synapse-specific gene expression during development of the neuromuscular junction.

Adult skeletal muscle locally expresses nicotinic acetylcholine receptors (nAChRs) at the neuromuscular junction by selective induction of their subunit-encoding genes (alpha beta epsilon delta) in endplate-associated myonuclei. Neuregulin/ARIA is a nerve-derived factor that is thought to be largely responsible for this local gene induction. Neuregulin/ARIA activates a Ras/MAP kinase signalling cascade, which ultimately induces nAChR epsilon-subunit gene expression via a 15 bp sequence that harbors a core Ets transcription factor binding site (GGA). Interestingly, this same sequence also appears to participate in extrajunctional repression of the epsilon-subunit gene. Muscle Ets 2 overexpression induces nAChR epsilon-subunit gene promoter activity, whereas a dominant/negative Ets blocks neuregulin-dependent induction. These results suggest that Ets transcription factors play a role in mediating synapse-specific and neuregulin-mediated motor neuron control of nAChR gene expression.

Effect of dexamethasone on T-cell receptor/CD3 expression.

Glucocorticoid hormones (GCH) are anti-inflammatory and immunosuppressive agents that inhibit T-cell growth and activation. Since the T-cell receptor (TCR)/CD3 complex mediates T-lymphocyte activation, we studied the effect of in vitro dexamethasone (DEX), a synthetic GCH, on TCR/CD3 expression. DEX-treatment of a hybridoma T-cell line and normal un-transformed T-cell clones induced a decrease of the TCR/ CD3 membrane expression after 4 days. After 4 weeks, TCR/CD3 was undetectable. However, the amount of mRNAs coding TCR/CD3 chains, including TCR alpha, TCR beta, CD3 gamma, CD3 theta and CD3 epsilon, as well as the amount of CD3 epsilon protein, a major component of the complex, were unaltered. By contrast, a decrease of the mRNAs deriving from the TCR zeta gene locus, as well as of the TCR zeta protein which is responsible for the membrane expression of the TCR/CD3 complex, was induced. These data suggest that the down-modulation of TCR expression is due to the diminution of TCR zeta gene products in DEX-treated cells.

Recombinant toluene-4-monooxygenase: catalytic and Mössbauer studies of the purified diiron and rieske components of a four-protein complex.

Expression of the tmoA-F gene cluster from Pseudomonas mendocina KRI in Escherichia coli BL21(DE3) produces a catalytically active form of the toluene-4-monooxygenase (T4MO) complex. Here we report the purification and characterization of four soluble proteins required for the in vitro reconstitution of T4MO catalytic activity. These proteins are a diiron hydroxylase (T4MOH), a Riesketype ferredoxin (T4MOC), an effector protein (T4MOD), and an NADH oxidoreductase (T4MOF). The T4MOH component is composed of the tmoA, tmoB, and tmoE gene products [quaternary structure (alpha beta epsilon)2, Mr approximately 220 kDa]. The T4MOA polypeptide contains two copies of the amino acid sequence motif (D/E)X(28-37)DEXRH; the same motif provides all of the protein-derived ligands to the diiron centers of ribonucleotide reductase, the soluble methane monooxygenase, and the stearoyl-ACP delta 9 desaturase. Mössbauer, optical, and EPR measurements show that the T4MOH contains diiron centers and suggest that the diiron center contains hydroxo bridge(s) in the diferric state, as observed for methane monooxygenase. Mössbauer and EPR measurements also show that the T4MOC contains a Rieske-type iron-sulfur center. This assignment is in accord with the presence of the amino acid sequence motif CPHX(15-17)CX2H, which has also been found in the bacterial, chloroplastic, and mitochondrial Rieske proteins as well as the bacterial NADH-dependent cis-dihydrodiol-forming aromatic dioxygenases. While single-turnover catalytic studies confirm the function of the T4MOH as the hydroxylase, the NADH-dependent multiple-turnover hydroxylation activity is increased by more than 100-fold in the presence of the T4MOC, which mediates highly specific electron transfer between the T4MOF and the T4MOH. The T4MOD can be purified as an 11.6 kDa monomeric protein devoid of cofactors or redox-active metal ions; this component is also detected as a substoichiometric consitutent of the purified T4MOH. The rate of the hydroxylation reaction can be mildly stimulated by the further addition of separately purified T4MOD to the T4MOH, implying the formation of a high affinity, catalytically competent complex between these two components. These characterizations define a novel, four-component oxygenase combining elements from the soluble methane oxidation complex of the methanotrophic bacteria and the aromatic hydroxylation complexes of the soil pseudomonads.

Asymmetry of Escherichia coli F1-ATPase as a Function of the Interaction of α-β Subunit Pairs with the γ and ∊ Subunits

The asymmetry of Escherichia coli F1-ATPase (ECF1) has been explored in chemical modification experiments involving two mutant enzyme preparations. One mutant contains a cysteine (Cys) at position 149 of the beta subunit, along with conversion of a Val to Ala at residue 198 to suppress the deleterious effect of the Cys for Gly at 149 mutation (mutant beta G149C:V198A). The second mutant has these mutations and also Cys residues at positions 381 of beta and 108 of the epsilon subunit (mutant beta G149C:V198A:E381C/epsilon S108C). On CuCl2 treatment of this second mutant, there is cross-linking of one copy of the beta subunit to gamma via the Cys at 381, a second to the epsilon subunit (between beta Cys381 and epsilon Cys108), while the third beta subunit in the ECF1 complex is mostly free (some cross-linking to delta); thereby distinguishing the three beta subunits as beta gamma, beta epsilon, and beta free, respectively. Both mutants have ATPase activities similar to wild-type enzyme. Under all nucleotide conditions, including with essentially nucleotide-free enzyme, the three different beta subunits were found to react differently with N-ethylmaleimide (NEM) which reacts with Cys149, dicyclohexyl carbodiimide (DCCD) which reacts with Glu192, and 7-chloro-4-nitrobenzofurazan (NbfCl) which reacts with Tyr297. Thus, beta gamma reacted with DCCD but not NEM or NbfCl; beta free was reactive with all three reagents; beta epsilon reacted with NEM, but was poorly reactive to DCCD or NbfCl. There was a strong nucleotide dependence of the reaction of Cys149 in beta epsilon (but not in beta free) with NEM, indicative of the important role that the epsilon subunit plays in functioning of the enzyme.

ARIA is concentrated in nerve terminals at neuromuscular junctions and at other synapses

Skeletal muscle ACh receptors (AChRs) accumulate at neuromuscular junctions (nmjs) at least partly because of the selective induction of AChR subunit genes in subsynaptic myotube nuclei by the motor nerve terminal. Additionally, mammalian AChRs undergo a postnatal change in subunit composition from embryonic (alpha 2 beta gamma delta) to adult (alpha 2 beta epsilon delta) forms, a switch that also depends on innervation. ARIA, a protein purified from chicken brains based on its ability to induce AChR synthesis in primary chick muscle cells, is a strong candidate for being the molecule responsible for these early developmental events. ARIA mRNA has been detected in embryonic motor neurons during synapse formation, and the gene continues to be expressed postnatally. In this report, we provide evidence that ARIA-like immunoreactivity is concentrated in rat motor nerve terminals from early postnatal ages, and that it can be detected in motor neurons in E18 embryos. ARIA is also detectable in axons within colchicine-treated sciatic nerves, suggesting that the protein in the nerve terminal has been transported from the cell body. ARIA mRNA is present in, but not restricted to, cholinergic neurons. Likewise, we report here that ARIA-like immunoreactivity is present in some noncholinergic central synapses. We also present evidence that isoforms of ARIA are differentially distributed among functionally distinct classes of neurons.

Green function analysis of energy spectra scaling properties

The relation between the singularities of multifractal energy spectral measures and the behaviours of the Green function is studied in the framework of a tight-binding Hamiltonian. If the measure mu (E) has a seating behaviour at energy E of the form Delta mu (E)= mu (E+ delta )- mu (E- delta ) varies as delta alpha (E), it is proved that the imaginary part of the Green function P(E, epsilon ) scales as P(E, epsilon ) varies as epsilon beta (E) with beta (E)= alpha (E)+1, the reverse being also true. This is exemplified in the case of the density of states and the local density of states of the one-dimensional Fibonacci quasicrystalline chain.

Protein-tyrosine phosphatases specifically regulate muscle adult-type nicotinic acetylcholine receptor gene expression.

Innervation of skeletal muscles results in expression of adult-type nicotinic acetylcholine receptors (alpha 2 beta epsilon delta) beneath the neuromuscular junction. This local expression is largely a result of selective induction of adult-type nicotinic acetylcholine receptor (nAChR) genes in endplate-associated myonuclei. The molecular mechanism by which the nerve induces gene expression in these nuclei is not known. We have shown previously that ionophore-induced calcium influx across the plasma membrane preferentially decreases expression from the adult-type specific nAChR epsilon-subunit gene (Walke, W., Staple, J., Adams, L., Gnegy, M., Chahine, K., and Goldman, D. (1994) J. Biol. Chem. 269, 19447-19456). Here we provide evidence that the genes encoding adult-type nAChRs are specifically regulated by protein-tyrosine phosphatase activity. Orthovanadate, a specific protein-tyrosine phosphatase inhibitor, caused increased expression of the epsilon-subunit gene in rat primary myotubes and was able to completely block the suppressive effects of increased calcium influx on epsilon-subunit RNA expression. Overexpression of protein-tyrosine phosphatases selectively decreased expression from the adult-type nAChR genes with no effect on the embryonic-type specific gamma-subunit gene. These results demonstrate that protein-tyrosine phosphatases regulate mammalian adult-type nAChR gene expression and suggest a mechanism by which muscle innervation selectively regulates gene expression in endplate-associated myonuclei.

Effects of insulin on diacylglycerol/protein kinase-C signalling and glucose transport in rat skeletal muscles in vivo and in vitro.

Insulin treatment in vivo provoked rapid dose-related increases in diacylglycerol content and/or translocation of protein kinase-C (PKC) from cytosol to membranes in rat soleus and gastrocnemius muscles. These effects were apparent with 1) insulin doses that provoked submaximal and maximal increases in glucose utilization, and 2) glucose-stimulated endogenous insulin secretion. Insulin-stimulated PKC translocation was evident when PKC was assayed by 1) histone or protamine phosphorylation after PKC purification by Mono Q column chromatography, and 2) immunoblotting for PKC beta and PKC epsilon. Dose-related effects of insulin on PKC translocation were also observed in the rat soleus in vitro, and this was associated with increased phosphorylation of 40- and 80-kilodalton proteins, which were also phosphorylated by phorbol ester treatment. A role for diacylglycerol-PKC signalling in insulin-stimulated glucose transport was suggested by studies of [3H]2-deoxyglucose ([3H]2-DOG) uptake in the rat soleus in vitro in that 1) PKC translocation and 2-DOG uptake were correlated; and 2) stimulatory effects of insulin and phorbol esters on 2-DOG uptake were apparently nonadditive.

Characterization of semi-uncoupled hybrid Escherichia coli-Bacillus megaterium F1F0 proton-translocating ATPases.

Cloned atp genes for the proton-translocating ATPase of the obligate aerobe Bacillus megaterium have been demonstrated to be capable of complementing Escherichia coli ATPase (unc) mutants (Hawthorne, C. A., and Brusilow, W. S. A. (1986) J. Biol. Chem. 261, 5245-5248). To determine the minimum subunit requirements for cross-species complementation, we constructed all combinations of B. megaterium atpA, G, D, and C genes (coding for the alpha, gamma, beta, and epsilon subunits, respectively) and tested their abilities to complement two uncA (alpha subunit) and two uncD (beta subunit) mutants of E. coli. The results indicated that complementation of either uncD mutant required atpD (beta) only. Complementation of one of the uncA (alpha) mutants required atpA, G, and D (alpha, gamma, and beta) and possibly atpE (epsilon) as well. The other uncA mutant was not complemented by any combination of B. megaterium ATPase genes. Complementation of a beta mutant by atpD (beta) or atpD and C (beta epsilon) produced cells which could grow aerobically on a nonfermentable carbon source (succinate) but not anaerobically on rich medium containing glucose. These E. coli therefore had become obligate aerobes. The ability to grow anaerobically could be restored to the mutant complemented by atpD alone by growth at pH 7.5 or pH 8 in the presence of 0.1 M potassium.

Acetylcholine receptor-inducing activity stimulates expression of the epsilon-subunit gene of the muscle acetylcholine receptor.

Motor neurons regulate the transcription of acetylcholine receptor subunit genes in postsynaptic muscle fibers both through muscle electrical activity produced by motor neuron acetylcholine release and by mechanisms independent of such transmitter release. Factors secreted by the motor neuron may mediate activity-independent regulation, including the postnatal switch from alpha 2 beta gamma delta (embryonic type) to alpha 2 beta epsilon delta (adult type) receptors. We have investigated the effect of putative trophic factors, agents affecting second-messenger systems, and muscle activity on the levels of acetylcholine receptor subunit mRNAs in primary mouse muscle cultures. We found that ARIA (acetylcholine receptor-inducing activity), a 42-kDa glycoprotein purified on the basis of its ability to increase the synthesis of acetylcholine receptors in chick myotubes, increases epsilon-subunit mRNA levels up to 10-fold. In addition, ARIA stimulated alpha-, gamma-, and delta-subunit mRNA levels 2-fold but had no effect on the expression of the beta-subunit gene. These effects of ARIA were independent of muscle activity, and they were not mimicked by calcitonin gene-related peptide nor by thyroxine, forskolin, phorbol 12-myristate 13-acetate, the calcium ionophore A23187, basic fibroblast growth factor, or transforming growth factor beta. Based on these data, we suggest that ARIA may act at the mammalian neuromuscular junction to induce adult-type acetylcholine receptors.

Extracellular domains mediating ɛ subunit interactions of muscle acetylcholine receptor

Ligand-gated ion channels, a major class of cell-surface proteins, have a pseudosymmetric structure with five highly homologous subunits arranged around a central ion pore. The correct assembly of each channel, whose subunit composition varies with cell type and stage of development, requires specific recognition between the subunits. Assembly of the pentameric form of the acetylcholine receptor from adult muscle (AChR; alpha 2 beta epsilon delta) proceeds by a stepwise pathway starting with the formation of the heterodimers, alpha epsilon and alpha delta. The heterodimers than associate with the beta subunit and with each other to form the complete receptor. We have now determined which parts of the subunits mediate the interactions during assembly of the adult form of the receptor from mouse muscle by using a chimaeric subunit in which the N-terminal and C-terminal extracellular domains are derived from the epsilon subunit with the remainder from the beta subunit. The epsilon and beta subunits were chosen because the epsilon subunit forms a heterodimer with the alpha subunit in the pathway for assembly of the receptor, whereas the beta subunit does not. The epsilon beta chimera can substitute for the epsilon but not the beta subunit in the oligomeric receptor, indicating that the alpha subunit specifically recognizes an extracellular domain of the epsilon subunit.