Mice lacking the M3 muscarinic acetylcholine receptor are hypophagic and lean

Members of the muscarinic acetylcholine receptor family (M1-M5) have central roles in the regulation of many fundamental physiological functions. Identifying the specific receptor subtype(s) that mediate the diverse muscarinic actions of acetylcholine is of considerable therapeutic interest, but has proved difficult primarily because of a lack of subtype-selective ligands. Here we show that mice deficient in the M3 muscarinic receptor (M3R-/- mice) display a significant decrease in food intake, reduced body weight and peripheral fat deposits, and very low levels of serum leptin and insulin. Paradoxically, hypothalamic messenger RNA levels of melanin-concentrating hormone (MCH), which are normally upregulated in fasted animals leading to an increase in food intake, are significantly reduced in M3R-/- mice. Intra-cerebroventricular injection studies show that an agouti-related peptide analogue lacked orexigenic (appetite-stimulating) activity in M3R-/- mice. However, M3R-/- mice remained responsive to the orexigenic effects of MCH. Our data indicate that there may be a cholinergic pathway that involves M3-receptor-mediated facilitation of food intake at a site downstream of the hypothalamic leptin/melanocortin system and upstream of the MCH system.

Escherichia coli CspA-family RNA chaperones are transcription antiterminators

CspA, the major cold-shock protein of Escherichia coli, is an RNA chaperone, which is thought to facilitate translation at low temperature by destabilizing mRNA structures. Here we demonstrate that CspA, as well as homologous RNA chaperones CspE and CspC, are transcription antiterminators. In vitro, the addition of physiological concentrations of recombinant CspA, CspE, or CspC decreased transcription termination at several intrinsic terminators and also decreased transcription pausing. In vivo, overexpression of cloned CspC and CspE at 37 degrees C was sufficient to induce transcription of the metY-rpsO operon genes nusA, infB, rbfA, and pnp located downstream of multiple transcription terminators. Similar induction of downstream metY-rpsO operon genes was observed at cold shock, a condition to which the cell responds by massive overproduction of CspA. The products of nusA, infB, rbfA, and pnp-NusA, IF2, RbfA, and PNP-are known to be induced at cold shock. We propose that the cold-shock induction of nusA, infB, rbfA, and pnp occurs through transcription antitermination, which is mediated by CspA and other cold shock-induced Csp proteins.

Enhancement of D1 dopamine receptor-mediated locomotor stimulation in M(4) muscarinic acetylcholine receptor knockout mice

Muscarinic acetylcholine receptors (M(1)-M(5)) regulate many key functions of the central and peripheral nervous system. Primarily because of the lack of receptor subtype-selective ligands, the precise physiological roles of the individual muscarinic receptor subtypes remain to be elucidated. Interestingly, the M(4) receptor subtype is expressed abundantly in the striatum and various other forebrain regions. To study its potential role in the regulation of locomotor activity and other central functions, we used gene-targeting technology to create mice that lack functional M(4) receptors. Pharmacologic analysis of M(4) receptor-deficient mice indicated that M(4) receptors are not required for muscarinic receptor-mediated analgesia, tremor, hypothermia, and salivation. Strikingly, M(4) receptor-deficient mice showed an increase in basal locomotor activity and greatly enhanced locomotor responses (as compared with their wild-type littermates) after activation of D1 dopamine receptors. These results indicate that M(4) receptors exert inhibitory control on D1 receptor-mediated locomotor stimulation, probably at the level of striatal projection neurons where the two receptors are coexpressed at high levels. Our findings offer new perspectives for the treatment of Parkinson's disease and other movement disorders that are characterized by an imbalance between muscarinic cholinergic and dopaminergic neurotransmission.

Acquirement of cold sensitivity by quadruple deletion of the cspA family and its suppression by PNPase S1 domain in Escherichia coli

Escherichia coli contains a large CspA family, CspA to CspI. Here, we demonstrate that E. coli is highly protected against cold-shock stress, as these CspA homologues existed at approximately a total of two million molecules per cell at low temperature and growth defect was not observed until four csp genes (cspA, cspB, cspE and cspG) were deleted. The quadruple-deletion strain acquired cold sensitivity and formed filamentous cells at 15 degrees C although chromosomes were normally segregated. The cold-sensitivity and filamentation phenotypes were suppressed by all members of the CspA family except for CspD, which causes lethality upon overexpression. Interestingly, the cold sensitivity of the mutant was also suppressed by the S1 domain of polynucleotide phosphorylase (PNPase), which also folds into a beta-barrel structure similar to that of CspA. The present results show that cold-shock proteins and S1 domains share not only the tertiary structural similarity but also common functional properties, suggesting that these seemingly distinct protein categories may have evolved from a common primordial RNA-binding protein.

SARS-CoV-2 envelope protein causes acute respiratory distress syndrome (ARDS)-like pathological damages and constitutes an antiviral target

Cytokine storm and multi-organ failure are the main causes of SARS-CoV-2-related death. However, the origin of excessive damages caused by SARS-CoV-2 remains largely unknown. Here we show that the SARS-CoV-2 envelope (2-E) protein alone is able to cause acute respiratory distress syndrome (ARDS)-like damages in vitro and in vivo. 2-E proteins were found to form a type of pH-sensitive cation channels in bilayer lipid membranes. As observed in SARS-CoV-2-infected cells, heterologous expression of 2-E channels induced rapid cell death in various susceptible cell types and robust secretion of cytokines and chemokines in macrophages. Intravenous administration of purified 2-E protein into mice caused ARDS-like pathological damages in lung and spleen. A dominant negative mutation lowering 2-E channel activity attenuated cell death and SARS-CoV-2 production. Newly identified channel inhibitors exhibited potent anti-SARS-CoV-2 activity and excellent cell protective activity in vitro and these activities were positively correlated with inhibition of 2-E channel. Importantly, prophylactic and therapeutic administration of the channel inhibitor effectively reduced both the viral load and secretion of inflammation cytokines in lungs of SARS-CoV-2-infected transgenic mice expressing human angiotensin-converting enzyme 2 (hACE-2). Our study supports that 2-E is a promising drug target against SARS-CoV-2.

Response of Soil Microbial Communities to Elevated Antimony and Arsenic Contamination Indicates the Relationship between the Innate Microbiota and Contaminant Fractions

Mining of sulfide ore deposits containing metalloids, such as antimony and arsenic, has introduced serious soil contamination around the world, posing severe threats to food safety and human health. Hence, it is important to understand the behavior and composition of the microbial communities that control the mobilization or sequestration of these metal(loid)s. Here, we selected two sites in Southwest China with different levels of Sb and As contamination to study interactions among various Sb and As fractions and the soil microbiota, with a focus on the microbial response to metalloid contamination. Comprehensive geochemical analyses and 16S rRNA gene amplicon sequencing demonstrated distinct soil taxonomic inventories depending on Sb and As contamination levels. Stochastic gradient boosting indicated that citric acid extractable Sb(V) and As(V) contributed 5% and 15%, respectively, to influencing the community diversity. Random forest predicted that low concentrations of Sb(V) and As(V) could enhance the community diversity but generally, the Sb and As contamination impairs microbial diversity. Co-occurrence network analysis indicated a strong correlation between the indigenous microbial communities and various Sb and As fractions. A number of taxa were identified as core genera due to their elevated abundances and positive correlation with contaminant fractions (total Sb and As concentrations, bioavailable Sb and As extractable fractions, and Sb and As redox species). Shotgun metagenomics indicated that Sb and As biogeochemical redox reactions may exist in contaminated soils. All these observations suggest the potential for bioremediation of Sb- and As-contaminated soils.

Distribution of four polymorphisms in the tumour necrosis factor (TNF) genes in patients with inflammatory bowel disease (IBD)

In 153 patients with IBD, 64 with Crohn's disease (CD), and 89 with ulcerative colitis (UC), as well as in 54 healthy controls (HC), the frequencies of four known di-allelic polymorphisms in the genes for TNF-alpha and lymphotoxin alpha (LTalpha) were investigated. In the Dutch population, the alleles of these four polymorphisms are present in only five combinations, called TNF haplotypes: TNF-C, -E, -H, -I, -P. Furthermore, the relation with the presence of perinuclear anti-neutrophil cytoplasmic autoantibodies (P-ANCA) was studied. A small, but statistically significant, association between the polymorphism at position -308 in the promoter region of the TNF-alpha gene and UC was found. The frequency of the uncommon TNF-alpha -308 allele 2 was found to be decreased in patients with UC compared with HC (allele frequency of allele 2 in UC patients 0-15 versus 0.25 in HC, P=0.044). No significant differences in distribution of the TNF haplotypes were found between IBD patients and HC, although there was a tendency towards a higher frequency of the TNF-C haplotype in UC patients compared with controls (haplotype frequency 22% versus 13%; P=0.19). No statistically significant differences in distribution of the TNF haplotypes were observed between P-ANCA-positive and P-ANCA-negative UC patients. The strength of the associations indicates that TNF genes are not markers for the predisposition to suffer from IBD. They may, however, be markers of subsets of patients with UC and CD.

Amino acid residues in Anabaena ferredoxin crucial to interaction with ferredoxin-NADP+ reductase: site-directed mutagenesis and laser flash photolysis

Ferredoxin (Fd) functions in photosynthesis to transfer electrons from photosystem I to ferredoxin-NADP+ reductase (FNR). We have made several site-directed mutants of Anabaena 7120 Fd and have used laser flash photolysis to investigate the effects of these mutations on the kinetics of reduction of oxidized Fd by deazariboflavin semiquinone (dRfH.) and the reduction of oxidized Anabaena FNR by reduced Fd. None of the mutations influenced the second-order rate constant for dRfH. reduction by more than a factor of 2, suggesting that the ability of the [2Fe-2S] cluster to participate in electron transfer was not seriously affected. In contrast, a surface charge reversal mutation, E94K, resulted in a 20,000-fold decrease in the second-order rate constant for electron transfer from Fd to FNR, whereas a similar mutation at an adjacent site, E95K, produced little or no change in reaction rate constant compared to wild-type Fd. Such a dramatic difference between contiguous surface mutations suggests a very precise surface complementarity at the protein-protein interface. Mutations introduced at F65 (F65I and F65A) also decreased the rate constant for the Fd/FNR electron transfer reaction by more than 3 orders of magnitude. Spectroscopic and thermodynamic measurements with both the E94 and F65 mutants indicated that the kinetic differences cannot be ascribed to changes in gross conformation, redox potential, or FNR binding constant but rather reflect the protein-protein interactions that control electron transfer. Several mutations at other sites in the vicinity of E94 and F65 (R42, T48, D68, and D69) resulted in little or no perturbation of the Fd/FNR interaction.(ABSTRACT TRUNCATED AT 250 WORDS)

A two-species test of the hypothesis that spatial isolation influences microbial diversity in soil

The hypothesis that spatial isolation is a key determinant of microbial community structure in soils was evaluated by examining the competitive dynamics of two species growing on a single resource in a uniform sand matrix under varied moisture content. One species dominated the community under highly connected, saturated treatments, suggesting that these conditions allow competitive interactions to structure the community. As moisture content decreased, however, the less competitive species became established in the community. This effect was most pronounced at a matric water potential of -0.14 MPa where estimates of final population density and species fitness were equal. A second but more closely related species pair exhibited a similar response to decreasing moisture, suggesting that the effects of spatial isolation we observed are not simply a species-pair-specific phenomenon. These findings indicate that spatial isolation, created by low moisture content, plays an important role in structuring soil microbial communities.

Structure-function relationships in Anabaena ferredoxin: correlations between X-ray crystal structures, reduction potentials, and rate constants of electron transfer to ferredoxin:NADP+ reductase for site-specific ferredoxin mutants

A combination of structural, thermodynamic, and transient kinetic data on wild-type and mutant Anabaena vegetative cell ferredoxins has been used to investigate the nature of the protein-protein interactions leading to electron transfer from reduced ferredoxin to oxidized ferredoxin:NADP+ reductase (FNR). We have determined the reduction potentials of wild-type vegetative ferredoxin, heterocyst ferredoxin, and 12 site-specific mutants at seven surface residues of vegetative ferredoxin, as well as the one- and two-electron reduction potentials of FNR, both alone and in complexes with wild-type and three mutant ferredoxins. X-ray crystallographic structure determinations have been carried out for six of the ferredoxin mutants. None of the mutants showed significant structural changes in the immediate vicinity of the [2Fe-2S] cluster, despite large decreases in electron-transfer reactivity (for E94K and S47A) and sizable increases in reduction potential (80 mV for E94K and 47 mV for S47A). Furthermore, the relatively small changes in Calpha backbone atom positions which were observed in these mutants do not correlate with the kinetic and thermodynamic properties. In sharp contrast to the S47A mutant, S47T retains electron-transfer activity, and its reduction potential is 100 mV more negative than that of the S47A mutant, implicating the importance of the hydrogen bond which exists between the side chain hydroxyl group of S47 and the side chain carboxyl oxygen of E94. Other ferredoxin mutations that alter both reduction potential and electron-transfer reactivity are E94Q, F65A, and F65I, whereas D62K, D68K, Q70K, E94D, and F65Y have reduction potentials and electron-transfer reactivity that are similar to those of wild-type ferredoxin. In electrostatic complexes with recombinant FNR, three of the kinetically impaired ferredoxin mutants, as did wild-type ferredoxin, induced large (approximately 40 mV) positive shifts in the reduction potential of the flavoprotein, thereby making electron transfer thermodynamically feasible. On the basis of these observations, we conclude that nonconservative mutations of three critical residues (S47, F65, and E94) on the surface of ferredoxin have large parallel effects on both the reduction potential and the electron-transfer reactivity of the [2Fe-2S] cluster and that the reduction potential changes are not the principal factor governing electron-transfer reactivity. Rather, the kinetic properties are most likely controlled by the specific orientations of the proteins within the transient electron-transfer complex.

Structure-function studies of [2Fe-2S] ferredoxins

The ability to overexpress [2Fe-2S] ferredoxins in Escherichia coli has opened up exciting research opportunities. High-resolution x-ray structures have been determined for the wild-type ferredoxins produced by the vegatative and heterocyst forms of Anabaena strain 7120 (in their oxidized states), and these have been compared to structural information derived from multidimensional, multinuclear NMR spectroscopy. The electron delocalization in in these proteins in their oxidized and reduced states has been studied by 1H, 2H, 13C, and 15N NMR spectroscopy. Site-directed mutagenesis has been used to prepare variants of these ferredoxins. Mutants (over 50) of the vegetative ferredoxin have been designed to explore questions about cluster assembly and stabilization and to determine which residues are important for recognition and electron transfer to the redox partner Anabaena ferredoxin reductase. The results have shown that serine can replace cysteine at each of the four cluster attachment sites and still support cluster assembly. Electron transfer has been demonstrated with three of the four mutants. Although these mutants are less stable than the wild-type ferredoxin, it has been possible to determine the x-ray structure of one (C49S) and to characterize all four by EPR and NMR. Mutagenesis has identified residues 65 and 94 of the vegetative ferredoxin as crucial to interaction with the reductase. Three-dimensional models have been obtained by x-ray diffraction analysis for several additional mutants: T48S, A50V, E94K (four orders of magnitude less active than wild type in functional assays), and A43S/A45S/T48S/A50N (quadruple mutant).

Trends in the prevalence of peptic ulcer disease and Helicobacter pylori infection in family physician-referred uninvestigated dyspeptic patients in Hong Kong

BACKGROUND

Peptic ulcer disease is mainly caused by Helicobacter pylori infection and the use of non-steroidal anti-inflammatory drugs.

AIM

To investigate the trends in the prevalence of peptic ulcer disease, H. pylori infection and non-steroidal anti-inflammatory drug use in uninvestigated dyspeptic patients over recent years in Hong Kong.

METHODS

Data from consecutive patients with uninvestigated dyspeptic symptoms referred by family physicians for open access upper endoscopy during 1997 and 2003 were analysed in relation to peptic ulcer disease, H. pylori infection and non-steroidal anti-inflammatory drug use.

RESULTS

Among 2700 patients included, 405 (15%) had peptic ulcer disease and 14 (0.5%) had gastric cancer. There was a reduced trend from 1997 to 2003 in the prevalence of peptic ulcer disease (17, 20, 14, 16, 13, 14 and 14%, respectively, chi2 = 5.80, P = 0.016) (mainly because of decrease in duodenal ulcers), H. pylori infection (44, 50, 49, 44, 40, 40, 36 and 43%, respectively, chi2 = 13.55, P < 0.001) and non-steroidal anti-inflammatory drug use (13, 5, 5, 6, 3, 4, 4 and 5% respectively, chi2 = 13.61, P < 0.001). The prevalence of peptic ulcer disease, H. pylori infection and non-steroidal anti-inflammatory drug use between 2001 and 2003 were significantly lower than that between 1997 and 2000 (17% vs. 13%, OR = 0.78, 95% CI: 0.63-0.96, P = 0.020 for peptic ulcer disease; 47% vs. 39%, OR =0.72, 95% CI: 0.60-0.86, P < 0.001 for H. pylori infection; and 6% vs. 4%, OR = 0.56, 95% CI: 0.39-0.82, P = 0.002 for non-steroidal anti-inflammatory drug use). H. pylori infection was associated with both duodenal ulcer (OR = 15.87, 95% CI: 10.60-23.76, P < 0.001) and gastric ulcer (OR = 3.12, 95% CI: 2.15-4.53, P < 0.001) whereas non-steroidal anti-inflammatory drug use was only associated with gastric ulcer (OR = 2.97, 95% CI: 1.70-5.20, P < 0.001).

CONCLUSIONS

The prevalence of peptic ulcer disease, mainly duodenal ulcers, was reduced in association with a decreasing trend in the prevalence of H. pylori infection and non-steroidal anti-inflammatory drug use from 1997 to 2003.

Large exchange bias after zero-field cooling from an unmagnetized state

Exchange bias (EB) is usually observed in systems with an interface between different magnetic phases after field cooling. Here we report an unusual phenomenon in which a large EB can be observed in Ni-Mn-In bulk alloys after zero-field cooling from an unmagnetized state. We propose that this is related to the newly formed interface between different magnetic phases during the initial magnetization process. The magnetic unidirectional anisotropy, which is the origin of the EB effect, can be created isothermally below the blocking temperature.

Effects of topical treatment of sodium butyrate and 5-aminosalicylic acid on expression of trefoil factor 3, interleukin 1beta, and nuclear factor kappaB in trinitrobenzene sulphonic acid induced colitis in rats

BACKGROUND AND AIMS

Butyrate enemas have been shown to be effective in treatment of ulcerative colitis, but the mechanism of the effects of butyrate is not totally known. This study evaluates effects of topical treatment of sodium butyrate (NaB) and 5-aminosalicylic acid (5-ASA) on the expression of trefoil factor 3 (TFF3), interleukin 1beta (IL1beta), and nuclear factor kappaB (NFkappaB) in trinitrobenzene sulphonic acid (TNBS) induced colitis in rats.

METHODS

Distal colitis was induced in male Wistar rats by colonic administration of TNBS and colonically treated with NaB, 5-ASA, combination of NaB and 5-ASA, and normal saline for 14 consecutive days. Colonic damage score, tissue myeloperoxidase (MPO) activity, TFF3 mRNA expression, serum IL1beta production, and tissue NFkappaB expression were determined, respectively.

RESULTS

Treatment of NaB, 5-ASA, and the combination improved diarrhoea, colonic damage score, and MPO activities, increased TFF3 mRNA expression, and decreased serum IL1beta production and tissue NFkappaB expression. The combination therapy of NaB and 5-ASA had better effects than any other single treatment.

CONCLUSIONS

The combination of topical treatment of NaB and 5-ASA was effective for relieving and repairing colonic inflammation and the effects were related to stimulation of TFF3 mRNA expression and down-regulation of IL1beta production and NFkappaB expression.

Compromised BRCA1-PALB2 interaction is associated with breast cancer risk

The major breast cancer suppressor proteins BRCA1 and BRCA2 play essential roles in homologous recombination (HR)-mediated DNA repair, which is thought to be critical for tumor suppression. The two BRCA proteins are linked by a third tumor suppressor, PALB2, in the HR pathway. While truncating mutations in these genes are generally pathogenic, interpretations of missense variants remains a challenge. To date, patient-derived missense variants that disrupt PALB2 binding have been identified in BRCA1 and BRCA2; however, there has not been sufficient evidence to prove their pathogenicity in humans, and no variants in PALB2 that disrupt either its BRCA1 or BRCA2 binding have been reported. Here, we report on the identification of a novel PALB2 variant, c.104T>C [p.L35P], that segregated in a family with a strong history of breast cancer. Functional analyses showed that L35P abrogates the PALB2-BRCA1 interaction and completely disables its abilities to promote HR and confer resistance to platinum salts and PARP inhibitors. Whole-exome sequencing of a breast cancer from a c.104T>C carrier revealed a second, somatic, truncating mutation affecting PALB2, and the tumor displays hallmark genomic features of tumors with BRCA mutations and HR defects, cementing the pathogenicity of L35P. Parallel analyses of other germline variants in the PALB2 N-terminal BRCA1-binding domain identified multiple variants that affect HR function to varying degrees, suggesting their possible contribution to cancer development. Our findings establish L35P as the first pathogenic missense mutation in PALB2 and directly demonstrate the requirement of the PALB2-BRCA1 interaction for breast cancer suppression.

Optical, EPR, and 1H NMR spectroscopy of serine-ligated [2Fe-2S] ferredoxins produced by site-directed mutagenesis of cysteine residues in recombinant Anabaena 7120 vegetative ferredoxin

Anabaena 7120 vegetative ferredoxin is a plant-type [2Fe-2S] ferredoxin that contains only four cysteine residues. The four cysteines (Cys41, Cys46, Cys49, and Cys79), which ligate the iron-sulfur cluster, were mutated individually to serine. The wild-type and mutant apoprotein genes were overexpressed in Escherichia coli, and the iron-sulfur cluster was assembled in vitro by adding iron and sulfide. UV-vis, EPR, and 1H NMR spectra were recorded on the wild-type ferredoxin and mutants. The optical spectra of all mutant proteins, in the oxidized state, differed from that of wild-type ferredoxin. Three of the mutant proteins (Cys46Ser, Cys49Ser, and Cys79Ser) exhibited a rhombic EPR spectrum in the reduced state, but one (Cys41Ser) showed a near-axial EPR spectrum. The 1H NMR spectra of each of the four oxidized mutants contained a group of broad, hyperfine-shifted peaks between 20 and 30 ppm with anti-Curie temperature dependence. The pattern of these peaks was different for each mutant, and all were distinct from that of the wild-type ferredoxin. Because of problems with protein stability, it was possible to obtain NMR spectra of only two of the mutants when reduced. The downfield hyperfine 1H NMR spectrum of the reduced Cys46Ser mutant resembled that of wild-type ferredoxin, but that of the Cys49Ser mutant did not. The hyperfine-shifted resonances of the 1H NMR spectrum of the reduced Cys46Ser mutant were assigned on the basis of results from temperature dependence studies, measurements of nuclear Overhauser effect, and 1H NMR spectra of the mutant labeled with [beta-2H]cysteine. Four hyperfine-shifted peaks of reduced Cys49Ser at 298 K were observed at 173, 120, 32, and 18 ppm. These peaks exhibited Curie-type temperature dependence and were tentatively assigned to protons from residues coordinated to Fe(III). The reduced Cys49Ser mutant showed an additional 1H NMR peak at -15 ppm (at 298 K) with Curie-type temperature dependence whose origin is unknown at present. [2Fe-2S] clusters can be placed into three different classifications according to their EPR lines shapes, NMR spectra, and reduction potentials: plant type, vertebrate type, and Rieske type. The EPR and NMR results obtained here reveal that mutant Cys46Ser has a "plant-type" cluster but that mutant Cys49Ser has a "vertebrate-type" cluster. Cysteine to serine mutations have been employed in the past to probe whether particular cysteine residues participate as iron-sulfur ligands.(ABSTRACT TRUNCATED AT 400 WORDS)

Solution structure of Escherichia coli glutaredoxin-2 shows similarity to mammalian glutathione-S-transferases

Glutaredoxin 2 (Grx2) from Escherichia coli is distinguished from other glutaredoxins by its larger size, low overall sequence identity and lack of electron donor activity with ribonucleotide reductase. However, catalysis of glutathione (GSH)-dependent general disulfide reduction by Grx2 is extremely efficient. The high-resolution solution structure of E. coli Grx2 shows a two-domain protein, with residues 1 to 72 forming a classical "thioredoxin-fold" glutaredoxin domain, connected by an 11 residue linker to the highly helical C-terminal domain, residues 84 to 215. The active site, Cys9-Pro10-Tyr11-Cys12, is buried in the interface between the two domains, but Cys9 is solvent-accessible, consistent with its role in catalysis. The structures reveal the hither to unknown fact that Grx2 is structurally similar to glutathione-S-transferases (GST), although there is no obvious sequence homology. The similarity of these structures gives important insights into the functional significance of a new class of mammalian GST-like proteins, the single-cysteine omega class, which have glutaredoxin oxidoreductase activity rather than GSH-S-transferase conjugating activity. E. coli Grx 2 is structurally and functionally a member of this new expanding family of large glutaredoxins. The primary function of Grx2 as a GST-like glutaredoxin is to catalyze reversible glutathionylation of proteins with GSH in cellular redox regulation including stress responses.

Synthesis, redox properties, in vivo formation, and neurobehavioral effects of N-acetylcysteinyl conjugates of dopamine: possible metabolites of relevance to Parkinson's disease

A very early event in the pathogenesis of idiopathic Parkinson's disease (PD) has been proposed to be an elevated translocation of L-cysteine (CySH) and/or glutathione (GSH) into pigmented dopaminergic cell bodies in the substantia nigra (SN) in which cytoplasmic dopamine (DA) is normally autoxidized to DA-o-quinone as the first step in a reaction leading to black neuromelanin polymer. Such an elevated influx of CySH and GSH would be expected to initially result in formation of 5-S-cysteinyldopamine (5-S-CyS-DA) and 5-S-glutathionyldopamine (5-S-Glu-DA), respectively, and might account for the massive irreversible loss of GSH and progressive depigmentation of SN cells that occurs in the Parkinsonian brain. However, 5-S-Glu-DA has not been detected in the Parkinsonian brain. Furthermore, although the 5-S-CyS-DA/DA and 5-S-CyS-DA/homovanillic acid concentration ratios increase significantly in the SN and cerebrospinal fluid, respectively, of PD patients, the absolute concentrations of 5-S-CyS-DA are extremely low and similar to those measured in age-matched control patients. One explanation for these observations is that 5-S-CyS-DA might be intraneuronally oxidized to more complex cysteinyldopamines and a number of dihydrobenzothiazines (DHBTs) and benzothiazines (BTs). Similarly, 5-S-Glu-DA might be intraneuronally oxidized to more complex glutathionyldopamines. In this investigation, however, it is demonstrated that 5-S-Glu-DA is rapidly metabolized in rat brain to 5-S-CyS-DA and 5-S-(N-acetylcysteinyl) dopamine (5) in reactions mediated by gamma-glutamyl transpeptidase (gamma-GT) and cysteine conjugate N-acetyltransferase. Similarly, 5-S-CyS-DA is metabolized to 5 in rat brain although more slowly than 5-S-Glu-DA. These reactions occur most rapidly in the midbrain, a region that contains the SN. Furthermore, 5, 2-S-(N-acetylcysteinyl)dopamine (6) and 2,5-di-S-(N-acetylcysteinyl)-dopamine (9) are toxic when administered into mouse brain having LD50 values of 14, 25, and 42 micrograms, respectively, and evoke a profound hyperactivity syndrome. These results suggest that the failure to detect 5-S-Glu-DA and the presence of only very low levels of 5-S-CyS-DA in Parkinsonian SN tissue and CSF might be related to both their intraneuronal oxidation and extraneuronal metabolism to N-acetylcysteinyl conjugates of DA. Furthermore, the toxic properties and neurobehavioral responses evoked by 5, 6, and 9 raise the possibility that these N-acetylcysteinyl conjugates of DA, in addition to certain cysteinyldopamines, DHBTs and BTs, might include endotoxins that contribute to SN cell death and other neuronal damage that occurs in PD. Methods are described for the synthesis of several N-acetylcysteinyl conjugates of DA, and their redox behaviors have been studied using cyclic voltammetry.

Protein expression, selective isotopic labeling, and analysis of hyperfine-shifted NMR signals of Anabaena 7120 vegetative [2Fe-2S]ferredoxin

Two alternative T7 RNA promoter/polymerase systems have been employed for the heterologous expression of a plant-type [2Fe-2S]ferredoxin, Anabaena 7120 vegetative ferredoxin, in Escherichia coli at high levels (approximately 20 mg/liter of culture). One system was used when 15N-labeling the ferredoxin uniformly by growing E. coli with 15NH4Cl as the nitrogen source; the other was used in conjunction with auxotrophic host strains to enrich the protein selectively by incorporating 2H-, 13C-, and 15N-labeled amino acids. The labeled ferredoxin samples were studied by 1H, 2H, 13C, and 15N NMR spectroscopy. Results from 1H and 2H NMR studies of samples containing [2H alpha]Cys, [2H beta 2, beta 3]Cys, [13 C beta]-Cys, and [15N]Cys have confirmed previous cysteinyl proton resonance assignments (L. Skjeldal, W. M. Westler, B.-H. Oh, A. M. Krezel, H. M. Holden, B. L. Jacobson, I. Rayment, and J. L. Markley (1991) Biochemistry 30, 7363-7368). All four 13C NMR peaks arising from the four cysteinyl beta-carbons and all four 15N NMR peaks from the four cysteinyl nitrogens were resolved in spectra of both the oxidized and reduced ferredoxins. The nitrogen resonance of Cys46, which is located in a unique (Ala-Cys) dipeptide, was assigned by detection of 13Ci-15Ni+1 coupling in a ferredoxin sample with incorporated [13C']Ala and [15N]Cys. The nitrogen signal of Cys 41 was assigned tentatively on the basis of its chemical shift and T1 relaxation time. The cysteinyl beta-carbon resonances in the reduced state have been assigned to individual residues on the basis of correlations with their (previously assigned) beta-protons. The beta-carbons resonance from Cys46 in the oxidized state has been assigned by its correlation with the corresponding resonance in the reduced state; this was accomplished by following the progressive air oxidation of a protein sample reduced by dithionite in the presence of methyl viologen. The spin-lattice relaxation times of the beta-carbons of the two cysteines coordinated to Fe)III) were similar in the oxidized and reduced states. This suggests that the antiferromagnetic coupling present in the reduced cluster has little influence on the electronic relaxation time of the Fe(III). Studies of the temperature dependence of the 1H, 13C, and 15N signals of the cysteinyl ligands to the [2Fe-2S] cluster show that the slope of the temperature dependence (delta delta/delta T-1) can be different for different atom types within a given residue. For example, in the reduced ferredoxin, although delta delta/delta T-1 is positive for Cys49 1H beta 2 and 1H beta 3, it is negative for Cys49 13C beta. Although delta delta/delta T-1 is negative for protons of cysteines ligated to Fe(II) and positive for protons of cysteines ligated to Fe(III), it is positive for all the cysteinyl nitrogens.(ABSTRACT TRUNCATED AT 400 WORDS)

Human ferredoxin: overproduction in Escherichia coli, reconstitution in vitro, and spectroscopic studies of iron-sulfur cluster ligand cysteine-to-serine mutants

Human ferredoxin, the human equivalent of bovine adrenodoxin, is a small iron-sulfur protein with one [2Fe-2S] cluster. It functions, as do other vertebrate ferredoxins, to transfer electrons during the processes of steroid hormone synthesis. A DNA fragment encoding the mature form of human ferredoxin was cloned into an expression vector under control of the T7 RNA polymerase/promoter system. The protein was overproduced in Escherichia coli, and the [2Fe-2S] cluster was incorporated into the protein by in vitro reconstitution. The overall yield was approximately 30 mg of purified, reconstituted ferredoxin per liter of culture. Four of the five cysteines in human ferredoxin are coordinated to the iron-sulfur cluster. First, the non-ligand cysteine (cysteine-95) was mutated to alanine, and then double mutants were created in which each of the other four cysteines (at positions 46, 52, 55, and 92) were mutated individually to serine. The wild-type ferredoxin and each of the five mutant proteins were studied by UV-visible spectroscopy and electron paramagnetic resonance spectroscopy. The EPR gav values of all five mutants were very similar to that of wild-type human ferredoxin. In the reduced state, three of the cysteine-to-serine mutants exhibited axial EPR spectra similar to that of wild-type, but one of the double mutants (C52S/C95A) exhibited a rhombic EPR spectrum. The UV-visible spectroscopic properties of the wild-type and the C95A mutant ferredoxins were identical, but those of the other cysteine-to-serine mutant proteins of human ferredoxin were quite different from those of the wild-type protein and each other. These results, along with those from cysteine-to-serine mutations in other ferredoxins, provide the basis for a more comprehensive theoretical and practical understanding of the features important to the ligation of [2Fe-2S] clusters, although they do not yet permit determination of which two cysteines ligate Fe(II) and which ligate Fe(III) in the reduced protein.

Generation and pharmacological analysis of M2 and M4 muscarinic receptor knockout mice

Muscarinic acetylcholine receptors (M1-M5) play important roles in the modulation of many key functions of the central and peripheral nervous system. To explore the physiological roles of the two Gi-coupled muscarinic receptors, we disrupted the M2 and M4 receptor genes in mice by using a gene targeting strategy. Pharmacological and behavioral analysis of the resulting mutant mice showed that the M2 receptor subtype is critically involved in mediating three of the most striking central muscarinic effects, tremor, hypothermia, and analgesia. These studies also indicated that M4 receptors are not critically involved in these central muscarinic responses. However, M4 receptor-deficient mice showed an increase in basal locomotor activity and greatly enhanced locomotor responses following drug-induced activation of D1 dopamine receptors. This observation is consistent with the concept that M4 receptors exert inhibitory control over D1 receptor-mediated locomotor stimulation, probably at the level of striatal projection neurons where the two receptors are known to be coexpressed. These findings emphasize the usefulness of gene targeting approaches to shed light on the physiological and pathophysiological roles of the individual muscarinic receptor subtypes.

Monodisperse polyethylene glycol diacrylate hydrogel microsphere formation by oxygen-controlled photopolymerization in a microfluidic device

PEG-based hydrogels have become widely used as drug delivery and tissue scaffolding materials. Common among PEG hydrogel-forming polymers are photopolymerizable acrylates such as polyethylene glycol diacrylate (PEGDA). Microfluidics and microfabrication technologies have recently enabled the miniaturization of PEGDA structures, thus enabling many possible applications for nano- and micro- structured hydrogels. The presence of oxygen, however, dramatically inhibits the photopolymerization of PEGDA, which in turn frustrates hydrogel formation in environments of persistently high oxygen concentration. Using PEGDA that has been emulsified in fluorocarbon oil via microfluidic flow focusing within polydimethylsiloxane (PDMS) devices, we show that polymerization is completely inhibited below critical droplet diameters. By developing an integrated model incorporating reaction kinetics and oxygen diffusion, we demonstrate that the critical droplet diameter is largely determined by the oxygen transport rate, which is dictated by the oxygen saturation concentration of the continuous oil phase. To overcome this fundamental limitation, we present a nitrogen micro-jacketed microfluidic device to reduce oxygen within the droplet, enabling the continuous on-chip photopolymerization of microscale PEGDA particles.

Iron-sulfur cluster cysteine-to-serine mutants of Anabaena -2Fe-2S- ferredoxin exhibit unexpected redox properties and are competent in electron transfer to ferredoxin:NADP+ reductase

The reduction potentials and the rate constants for electron transfer (et) to ferredoxin:NADP+ reductase (FNR) are reported for site-directed mutants of the [2Fe-2S] vegetative cell ferredoxin (Fd) from Anabaena PCC 7120, each of which has a cluster ligating cysteine residue mutated to serine (C41S, C46S, and C49S). The X-ray crystal structure of the C49S mutant has also been determined. The UV-visible optical and CD spectra of the mutants differ from each other and from wild-type (wt) Fd. This is a consequence of oxygen replacing one of the ligating cysteine sulfur atoms, thus altering the ligand --> Fe charge transfer transition energies and the chiro-optical properties of the chromophore. Each mutant is able to rapidly accept an electron from deazariboflavin semiquinone (dRfH.) and to transfer an electron from its reduced form to oxidized FNR although all are somewhat less reactive (30-50%) toward FNR and are appreciably less stable in solution than is wt Fd. Whereas the reduction potential of C46S (-381 mV) is not significantly altered from that of wt Fd (-384 mV), the potential of the C49S mutant (-329 mV) is shifted positively by 55 mV, demonstrating that the cluster potential is sensitive to mutations made at the ferric iron in reduced [2Fe-2S] Fds with localized valences. Despite the decrease in thermodynamic driving force for et from C49S to FNR, the et rate constant is similar to that measured for C46S. Thus, the et reactivity of the mutants does not correlate with altered reduction potentials. The et rate constants of the mutants also do not correlate with the apparent binding constants of the intermediate (Fdred:FNRox) complexes or with the ability of the prosthetic group to be reduced by dRfH.. Furthermore, the X-ray crystal structure of the C49S mutant is virtually identical to that of wt Fd. We conclude from these data that cysteine sulfur d-orbitals are not essential for et into or out of the iron atoms of the cluster and that the decreased et reactivity of these Fd mutants toward FNR may be due to small changes in the mutual orientation of the proteins within the intermediate complex and/or alterations in the electronic structure of the [2Fe-2S] cluster.