A Suppressor Screen of the Chimeric AtCNGC11/12 Reveals Residues Important for Intersubunit Interactions of Cyclic Nucleotide-Gated Ion Channels

To investigate the structure-function relationship of plant cyclic nucleotide-gated ion channels (CNGCs), we identified a total of 29 mutant alleles of the chimeric AtCNGC11/12 gene that induces multiple defense responses in the Arabidopsis (Arabidopsis thaliana) mutant, constitutive expresser of PR genes22 (cpr22). Based on computational modeling, two new alleles, S100 (AtCNGC11/12:G459R) and S137 (AtCNGC11/12:R381H), were identified as counterparts of human CNGA3 (a human CNGC) mutants. Both mutants lost all cpr22-mediated phenotypes. Transient expression in Nicotiana benthamiana as well as functional complementation in yeast (Saccharomyces cerevisiae) showed that both AtCNGC11/12:G459R and AtCNGC11/12:R381H have alterations in their channel function. Site-directed mutagenesis coupled with fast-protein liquid chromatography using recombinantly expressed C-terminal peptides indicated that both mutations significantly influence subunit stoichiometry to form multimeric channels. This observation was confirmed by bimolecular fluorescence complementation in planta. Taken together, we have identified two residues that are likely important for subunit interaction for plant CNGCs and likely for animal CNGCs as well.Cyclic nucleotide-gated ion channels (CNGCs) were first discovered in retinal photoreceptors and olfactory sensory neurons (Zagotta and Siegelbaum, 1996; Kaupp and Seifert, 2002). CNGCs play crucial roles for the signal transduction in these neurons that are excited by photons and odorants, respectively. In mammalian genomes, six CNGC genes have been found and named CNGA1 to CNGA4, CNGB1, and CNGB3 (Kaupp and Seifert, 2002). It has been reported that in mammalian cells, CNGCs function as heterotetramers that are composed of A and B subunits with cell-specific stoichiometry (Kaupp and Seifert, 2002; Cukkemane et al., 2011). For example, CNGCs in rod photoreceptors are composed of three A1 subunits and one B1a subunit, whereas in cone photoreceptors, they are believed to be composed of two A3 and two B3 subunits (Zhong et al., 2002; Peng et al., 2004). The structure of each subunit is similar to that of the voltage-gated K⁺-selective ion channel (Shaker) proteins, including a cytoplasmic N terminus, six membrane-spanning regions (S1–S6), a pore domain located between S5 and S6, and a cytoplasmic C terminus (Zagotta and Siegelbaum, 1996). However, CNGCs are only weakly voltage dependent and are opened by the direct binding of cyclic nucleotides (cAMP and cGMP), which are universally important secondary messengers that control diverse cellular responses (Fesenko et al., 1985). The cytoplasmic C terminus contains a cyclic nucleotide-binding domain (CNBD) and a C-linker region that connects the CNBD to the S6 domain. CNGC activity is also regulated by feedback inhibitory mechanisms involving the Ca²⁺ sensor protein, calmodulin (CaM). CaM-binding sites in animal CNGCs have been found in various regions of both the C- and N-terminal domains (Ungerer et al., 2011). It has been reported that the subunit composition has significant influence on the mode of CaM-mediated regulation (Kramer and Siegelbaum, 1992; Bradley et al., 2004; Song et al., 2008).On the other hand, plant CNGCs have only been investigated much more recently. The first plant CNGC, HvCBT1, was identified as a CaM-binding transporter protein in barley (Hordeum vulgare; Schuurink et al., 1998). Subsequently, several CNGCs were identified from Arabidopsis (Arabidopsis thaliana) and tobacco (Nicotiana tabacum; Arazi et al., 1999; Köhler and Neuhaus, 1998; Köhler et al., 1999). Interestingly, the Arabidopsis genome sequencing project identified a large family comprising 20 members (AtCNGC1–AtCNGC20), indicating a significant expansion of Arabidopsis CNGCs that suggests a higher level of diversity and functional importance in plants (Mäser et al., 2001). To date, possible biological functions of Arabidopsis CNGCs in development, ion homeostasis, thermal sensing, as well as pathogen resistance have been reported (Kaplan et al., 2007; Chin et al., 2009; Dietrich et al., 2010; Moeder et al., 2011; Finka et al., 2012). With respect to structure, plant CNGCs are believed to have a similar architecture to their animal counterparts (Chin et al., 2009). However, only a handful of studies on the structure-function analysis of plant CNGCs have been published so far, and this field is still very much in its infancy (Hua et al., 2003; Bridges et al., 2005; Kaplan et al., 2007; Baxter et al., 2008; Chin et al., 2010).Previously, we have reported two functionally important residues in plant CNGCs (Baxter et al., 2008; Chin et al., 2010). These residues were discovered using a suppressor screen of the rare gain-of-function Arabidopsis mutant constitutive expresser of PR genes22 (cpr22; Yoshioka et al., 2006). The cpr22 mutant, which has a deletion between AtCNGC11 and AtCNGC12 resulting in a novel but functional chimeric CNGC (AtCNGC11/12), exhibits multiple resistance responses without pathogen infection in the hemizygous state and conditional lethality in the homozygous state (Yoshioka et al., 2001, 2006; Moeder et al., 2011). It has been reported that the cpr22 phenotype is attributable to the expression of AtCNGC11/12 and its channel activity (Yoshioka et al., 2006; Baxter et al., 2008), thereby making the suppressor screen an invaluable tool for identifying intragenic mutants to further elucidate the structure-function relationship of plant CNGCs (Baxter et al., 2008; Chin et al., 2010).In this study, we describe a total of 29 mutant alleles of AtCNGC11/12, including the three previously published alleles (Baxter et al., 2008; Chin at al., 2010), and compare their predicted three-dimensional structural positions with equivalent mutations of a human CNGC, CNGA3. In this analysis, two AtCNGC11/12 mutations emerged as counterparts of human mutations (Wissinger et al., 2001). Both the AtCNGC11/12 as well as the human CNGA3 mutations were computationally predicted to affect intersubunit interactions. This prediction was experimentally validated by size-exclusion chromatography (FPLC) as well as bimolecular fluorescence complementation (BiFC) in combination with site-direct mutagenesis using recombinant C-terminal peptides.     

Sas20 is a highly flexible starch-binding protein in the Ruminococcus bromii cell-surface amylosome

Ruminococcus bromii is a keystone species in the human gut that has the rare ability to degrade dietary resistant starch (RS). This bacterium secretes a suite of starch-active proteins that work together within larger complexes called amylosomes that allow R. bromii to bind and degrade RS. Starch adherence system protein 20 (Sas20) is one of the more abundant proteins assembled within amylosomes, but little could be predicted about its molecular features based on amino acid sequence. Here, we performed a structure–function analysis of Sas20 and determined that it features two discrete starch-binding domains separated by a flexible linker. We show that Sas20 domain 1 contains an N-terminal β-sandwich followed by a cluster of α-helices, and the nonreducing end of maltooligosaccharides can be captured between these structural features. Furthermore, the crystal structure of a close homolog of Sas20 domain 2 revealed a unique bilobed starch-binding groove that targets the helical α1,4-linked glycan chains found in amorphous regions of amylopectin and crystalline regions of amylose. Affinity PAGE and isothermal titration calorimetry demonstrated that both domains bind maltoheptaose and soluble starch with relatively high affinity (K_d ≤ 20 μM) but exhibit limited or no binding to cyclodextrins. Finally, small-angle X-ray scattering analysis of the individual and combined domains support that these structures are highly flexible, which may allow the protein to adopt conformations that enhance its starch-targeting efficiency. Taken together, we conclude that Sas20 binds distinct features within the starch granule, facilitating the ability of R. bromii to hydrolyze dietary RS.     

Ultraviolet spectroscopy of anticonvulsant enaminones

The ultraviolet (UV) spectra of selected enaminones were determined in acidic, alkaline and neutral media and compared to their anticonvulsant activities. The wavelength of maximum absorption and molar absorptivity were compared with the anticonvulsant activity of the selected secondary and tertiary enaminones, and general inferences were made. The UV spectra of the enaminones had hypsochromic shifts in acidic media in comparison with neutral media. Generally, a small hypsochromic shift occurred in alkaline media when compared to the neutral solutions of the enaminones. The tertiary enaminones absorbed UV light at longer wavelength than the secondary enaminones in acidic, neutral and alkaline media. In particular, the tertiary enaminones displayed absorption at the higher end and secondary enaminones towards the lower end of the UV wavelength range 292-315nm in aqueous media. Tertiary enaminones (30-33) which were devoid of the NH proton were found to be uniformly inactive in a mouse model of electroshock seizures, while some secondary enaminones (1, 5-8, 12, 16, 18, 20, 23-25, 28 and 29) had anticonvulsant activity. Thus the NH group of secondary enaminones is very important for anticonvulsant activity, and this agrees with an already established trend in proton NMR spectroscopy. In addition, the para-substitution on the phenyl group in some enaminones result in higher molar absorptivity (epsilon) values that enhance anticonvulsant activity. These results indicate that the anticonvulsant activity of enaminones is not due to electronic effect alone, but is probably due to a combination of factors including electronic and steric effects, lipophilicity, and hydrogen bonding.     

Identification of a genetic marker associated with the resistance to Schistosoma mansoni infection using random amplified polymorphic DNA analysis

In schistosomiasis, the host/parasite interaction remains not completely understood. Many questions related to the susceptibility of snails to infection by respective trematode still remain unanswered. The control of schistosomiasis requires a good understanding of the host/parasite association. In this work, the susceptibility/resistance to Schistosoma mansoni infection within Biomphalaria alexandrina snails were studied starting one month post infection and continuing thereafter weekly up to 10 weeks after miracidia exposure. Genetic variations between susceptible and resistant strains to Schistosoma infection within B. alexandrina snails using random amplified polymorphic DNA analysis technique were also carried out. The results showed that 39.8% of the examined field snails were resistant, while 60.2% of these snails showed high infection rates.In the resistant genotype snails, OPA-02 primer produced a major low molecular weight marker 430 bp. Among the two snail strains there were interpopulational variations, while the individual specimens from the same snail strain, either susceptible or resistant, record semi-identical genetic bands. Also, the resistant character was ascendant in contrast to a decline in the susceptibility of snails from one generation to the next.     

Schistosome/mollusk: genetic compatibility

Schistosomiasis remains one of the most prevalent parasitic infections and has significant economic and public health consequences in many developing countries. Economic development and improvement in standard of living in these countries are dependent on the elimination of this odious disease. For the control of Schistosomiasis, understanding the host/parasite association is important, since the host parasite relationship is often complex and since questions remain concerning the susceptibility of snails to infection by respective trematodes and their specificity and suitability as hosts for continued parasite development. Thus, the long term aim of this research is to learn more about the genetic basis of the snail/parasite relationship with the hope of finding novel ways to disrupt the transmission of this disease. In the current research, genetic variability among susceptible and resistant strains within and between Biomphalaria glabrata and B. tenagophila was investigated using RAPD-PCR. The results indicate great genetic variations within the two snail species using three different primers (intrapopulational variations), while specimens from the same snail species showed few individual differences between the susceptible and resistant strains (interpopulational variation).     

Novel Regioselective Formation of S- and N-Hydroxyl-Alkyls of 5-(3-Chlorobenzo[b]Thien-2-yl)-3-Mercapto-4H-1,2,4-Triazole and A Facile Synthesis of Triazolo-Thiazoles and Thiazolo-Triazoles. Role of Catalyst and Microwave

Regioselective alkylation of 5-(3-chlorobenzo[b]thien-2-yl)-4H-1,2,4-triazole (1) with hydroxy alkylating agents 2, 3, 13, and the 2,3-O-isopropylidene-1-O-(p-tolylsulfonyl)-glycerol (10) afforded the corresponding S-alkylated derivatives 6, 7, 11, and 14 under both conventional and microwave irradiation conditions; bentonite as a solid support gave better results, with no change in regioselectivity. A facile intramolecular dehydrative ring closure of 6, 7, 11, and 14 using K₂CO₃ in DMF afforded the corresponding fused triazolo-thiazines and thiazolo-triazole 17–19. The isopropylidenes and acetyl derivatives of the products were prepared.     

Differentiation of Campylobacter Isolates on the Basis of Sensitivity to Boiling in Water as Measured by PCR-Detectable DNA

Differential sensitivity for the release of PCR-detectable genomic DNA upon boiling in water is reported for 45 Campylobacter jejuni and Campylobacter coli strains isolated in Egypt. All of the strains released PCR-detectable DNA when treated with proteinase K and sodium dodecyl sulfate. When DNA was extracted from these strains by boiling in water, nine (20%) of the strains were PCR negative or resistant to boiling, suggesting the presence of boiling-sensitive and boiling-resistant phenotypes.     

A new RNA picorna — Like virus in the cotton pink bollwormPectinophora gossypiella (Lep.: Gelechiidae) in Egypt

A new virus infecting the pink bollwormPectinophora gossypiella has been detected and purified from dead larvae collected from naturally infested cotton fields. The purified icosahedric virions measured 27±1 nm in diameter and contained RNA genome. Three capsid proteins of 31.7, 32.6 and 47.4 Kd have been separated on polyacrylamide gel. The purified virus was not highly infectious to the host larvae revealed while the pupal period survived from infected larvae was significantly prolonged. The virus particles infecting the midgut cells are grouped in paracrystallin arrays. The virus was vertically transmitted through infected adults. The main characteristics of this virus place are quite relative to the Picornavirus group.

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Résumé Un nouveau virus infectant le ver rose du cotonnier,Pectinophora gossypiella, a été isolé et purifié à partir de larves mortes récoltées en champ de coton. Les virions purifiés de 27±1 nm de diamètre, ont une forme icosaédrique et contiennent un génome à ARN. Trois protéines capsidaires de 31,7, 32,6 et 47,4 Kd ont été trouvées dans les virions. Le virus purifié n'est pas hautement infectieux pour les larves, cependant la durée du stade chrysalide est supérieure chez les lots infectés artificiellement. Dans les tissues atteints, les virions sont dispersés dans le cytoplasme des cellules de l'intestin ou bien groupés en amas paracrystallins de même type que chez d'autres insectes infectés avec des picornavirus. Les adultes malades transmettent ce virus à leur descendance. Par sa forme, sa taille et ses caractéristiques chimiques, ce virus libre peut être placé près des Picornavirus d'insectes.